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Abstract: All residential chimneys. both for fireplaces and appliances, are designed and constructed to serve the
same basic functions. They must provide fire protection and safely convey combustion by-products to the exterior
of the structure at a rate that does not adversely affect the combustion process. Design, materials selection,
construction, and building code requirements all have a significant impact on the chimney’s potential to fulfill these
functions. Chimney height and flue area are the two most critical factors in chimney desire.

Key Words: bricks, building codes, chimneys, draft, flashing, flues, masonry, mortar.

INTRODUCTION

This Technical Notes addresses the design and construction of residential chimneys. Other Technical Notes in
this Series deal with residential fireplaces and commercial chimneys. The design of residential chimneys is
empirical and based on successful prototypes. The function of residential chimneys is to allow combustion byproducts to be conducted away from the structure safely.

GENERAL

Residential chimneys generally fall into two categories: 1) chimneys serving fireplaces, and 2) chimneys serving
appliances. While there are dissimilarities between the two types, they both serve the same basic functions. It is
worthwhile, therefore, to consider their similarities. Both are constructed of similar materials and must meet the
same building code requirements. Even though they may convey different combustion by-products at different
velocities, they both must be designed and constructed to discharge these by-products at a rate that does not
adversely affect the combustion process and to release the discharged material at a height and location that
provides fire safety.

Flues may slope to join with other flues so as to discharge through a common flue, or to achieve the desired
location of the chimney. The maximum allowable slope is 30 deg from vertical. When combining flues the main
discharge flue should be sized for the maximum combined flow from the smaller flues. Combining flues of
dissimilar systems or fuels. i.e., appliances and fireplaces, is not allowed by many building codes. Separate flues
may be incorporated into one chimney so long as minimum wall thickness requirements are met and a full wythe
of brick is laid between them and bonded to the chimney walls.

Building Code Requirements

Building code requirements for chimneys may vary on a local basis. There are, however, several that are
accepted nearly everywhere. They include:

1. Chimney wall thickness should be a nominal 4 in. (100 mm) unless no flue liner is used, in which case a
nominal 8 in. (200 mm) is required.

2. Neither chimney nor flue liner may change size or shape within 6 in. (150 mm) of either floor components,
ceiling components or rafters.

3. The minimum chimney height for fire safety is the greater of 3 ft (1.0 m) above the highest point where the
chimney penetrates the roofline, or 2 ft (600 mm) higher than any portion of the structure or adjoining structures
within 10 ft (3.0 m) of the chimney, see Fig. 1.

4. Chimney clearance from combustible material is a minimum of 2 in. (50 mm) except where the chimney is
located entirely outside the structure, in which case 1 in. (25 mm) is acceptable.

5. The spaces between a chimney and combustible material should be firestopped using a minimum of 1-in. (25
mm) thick noncombustible material.

6. All exterior spaces between the chimney and adjacent components should be sealed. This is most commonly
accomplished by flashing and caulking.

7. Masonry chimneys should not be corbeled more than 6 in. (150 mm) from a wall or foundation nor should a
chimney be corbeled from a wall or foundation which is less than 12 in. (300 mm) in thickness unless it projects
equally on each side of the wall, except that on the second story of two-story dwellings corbeling of chimneys or
the exterior of the enclosing walls may equal the wall thickness. Corbeling may not exceed 1-in. (25 mm)
projection for each course of brick protected.

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Recommendations

In many situations it may be desirable to use the chimney as a structural element. This may be accomplished
within most building codes by maintaining the chimney wall thickness and adding a structural wall around the
chimney. This structural wall may be built integrally with the chimney wall. Most building codes require a minimum
of 4 in. (100 mm) of bearing. Considering all the building code dimensional requirements, the minimum wall
thickness of a lined chimney to be used as a structural component is 10 in. (250 mm) consisting of: 1) 4-in. (100
mm) chimney wall (brick), 2) 2-in. (50 mm) of noncombustible material (brick), and 3) 4-in. (100 mm) bearing
length (brick). An unlined chimney’s minimum wall thickness is 14-in. (350 mm) consisting of the same elements
as the lined chimney except that the chimney wall must be 8-in. (200 mm), see Fig. 2.

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MATERIALS

Brick

The chimney, by the nature of its function, is at least partially exposed to weathering. The brick should conform to
ASTM C 216, Grade SW, or ASTM C 62, Grade SW, to assure sufficient durability. Paving brick should conform
to ASTM C 902, Class SX.

Mortar

To allow for both weathering and thermal considerations, Type N portland cement-lime mortar is recommended
for the chimney. Type S portland cement-lime mortar is acceptable, and may be necessary when the chimney is
subjected to high lateral forces such as wind loads in excess of 25 psf (1.2 kPa) or seismic loads. Where the
chimney is in contact with earth, Type M portland cement-lime mortar is recommended. The mortar used to bed
the flue liners should be able to perform well under high temperatures. Therefore, fireclay mortars are highly
recommended. Type N portland cement-lime mortar is an acceptable substitute. For a comprehensive discussion
of portland cement-lime mortar types and uses, see Technical Notes 8 Series.

Flue Liners

Flue liners should conform to ASTM C 315. They should be thoroughly inspected just prior to installation for
cracks or other damage that might contribute to smoke and flue gas leakage.

Flashing

Corrosion-resistant sheet metal flashing is required by most building codes. Quality materials should be specified
since replacement may be expensive and troublesome. See Technical Notes 7A Revised for selection of flashing
materials.

Chimney Caps

A prefabricated chimney cap similar to the one shown in Fig. 3 should be used. This type cap provides better
durability and is more easily made water-resistant than a cast-in-place cap. When a cast-in-place cap is used, it
should incorporate the same shape as the prefabricated. The thickened sides and overhangs will reduce the
potential for water penetration.

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Rain Caps

Rain caps vary from sophisticated turbine type metal caps to simple slabs set above the termination point of the
flue liner. When specifying a manufactured rain cap, information regarding its effect on the gas flow through the
chimney should be obtained from the manufacturer. If the cap is metal, it should be corrosion-resistant.

Sealants

Caulking is frequently considered a means of correcting or hiding poor workmanship, rather than as an integral
part of construction. It should be detailed and installed with the same care as the other elements of the structure.
In all cases, the use of a good grade, polysulfide, butyl, or silicone rubber sealant is recommended. Oil-based
sealants should not be used. Regardless of the sealant used, proper priming and backing rope, are a must.

Ties and Reinforcement

Ties used in chimney construction should be corrosion-resistant metal ties. For a general discussion of ties and
their placement, refer to Technical Notes 28 Revised.
Reinforcing steel should conform to one of the following ASTM Standards:
1. Welded Wire-ASTM A 185
2. Steel Bar-ASTM A 615, ASTM A 616 or ASTM A 617
3. Wire-ASTM A 82

DESIGN

Design of fireplace and appliance chimneys is limited to the determination of height requirements that when used
in conjunction with proper flue sizes, detailing and construction will provide adequate draft. Building code
requirements for minimum chimney height remain in effect and must be met or exceeded.

Fireplace Chimneys

The design of residential fireplace chimneys is directly related to: 1) the area of the fireplace opening, 2) the area
of the flue liner, and 3) the height of the chimney. In most situations, the area of the fireplace opening is controlled
by considerations other than the performance of the system, such as aesthetics. The other components of the
system are usually designed based upon the desired fireplace opening.

A frontal face velocity of 0.80 ft per second (0.245 m/sec) at the fireplace opening has been accepted by the
American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) to be sufficient to prevent
smoke and gases from being discharged into habitable spaces. This is a minimum velocity and usually only
encountered while starting a fire. Flue liner size as a function of fireplace opening size may be obtained from
Technical Notes 19 Revised, Table 1.

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Appliance Chimneys

Appliance chimneys are divided into two types those venting one appliance, see Fig. 4, and those venting two or
more appliances, see Fig. 5. The two variables that are most commonly known to the designer are the input rating
and configuration of the system. Typical design criteria are shown in Tables 2 and 3. Building code requirements
for chimney heights should be considered as minimum heights for fire safety and should be strictly adhered to.

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General

Since both fireplace and appliance chimneys have an identical function, their construction methods and materials
are similar. Building code requirements insofar as construction is concerned are identical.
Fireplace Chimneys

General. The chimney of a fireplace is considered to be that portion of the fireplace from the base of the first flue
liner to the top of the last flue liner, or any rain cap above it.

Single-wythe chimneys should be attached to the structure. This is generally accomplished by using corrosionresistant metal ties spaced at a maximum of 24 in. (600 mm) on center. Multi-wythe chimneys that are not
masonry bonded should be bonded together using metal wire ties.

Racking. Chimneys are generally not as wide as the body of the fireplace below. When racking back to achieve
the desired dimensions or location of the chimney care must be exercised to insure that, since there is no
limitation on the distance each unit may be racked, cores of the units are not exposed. Preferred construction
consists of a setting bed over the racked face with uncored or paving brick set to provide a weather resistant
surface. Mortar washes may also be used. They may not, however, be as durable. When using a mortar wash it
should not bridge over the rack, but should fill each step individually. Both methods of racking are shown in Fig. 6.

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Flue Liners. The first flue liner should be supported along its entire perimeter by masonry. The liner should be
bedded in mortar with the joints cut flush and smoothed on the interior and the exterior joint area parged. The flue
liners should be set one section ahead of the chimney brickwork.

Flashing. Base flashing and counter flashing are installed at the chimney/roof interface, see Fig. 7. The base
flashing is installed first on the faces of the chimney perpendicular to the ridgeline with tabs at each corner. The
flashing should extend a minimum of 4 in. (100 mm) up the face of the chimney and along the roof. Counter
flashing is then installed over the base flashing. It is inserted into a mortar joint for 3/4 to 1 in. (19.1 mm to 25 mm)
and mortared solidly into the joint. The counter flashing should lap the base flashing by at least 3 in. (75 mm). If
the flashing is installed in sections, the flashing higher up the roofline should lap over the lower flashing a
minimum of 2 in. (50 mm). All joints in the base flashing and counter flashing should be thoroughly sealed. The
unexposed side of any bends in the flashing should also be sealed.

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Typical Section and Flashing Detail
FIG. 7

Cricket. If a cricket is desired, usually for chimneys whose dimension parallel to the ridgeline is greater than 30
in. (750 mm) and do not intersect the ridgeline, it should be constructed similar to the one shown in Fig. 8. The
dimensions of the cricket are based on the chimney measurements parallel to the ridgeline. The intersection of
the cricket and the chimney should be flashed and counter flashed in the same manner as a normal chimney roof
intersection. The flashing at the roofline should extend to at least 4 in. (100 mm) under the roofing material. For
dimensions and construction details, see Table 4, and Fig. 9.

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Chimney Caps. There are, as discussed in the materials section, two options regarding chimney caps: 1)
prefabricated, and 2) cast-in-place. Prefabricated caps generally provide superior performance as compared to
the cast-in-place type. Regardless of which type cap is used, it should be thoroughly primed, backed, and sealed
at the cap and flue liner interface to reduce the potential for water penetration.

Prefabricated caps are set in place on a mortar bed. There should be a bond break between the brickwork and
the setting bed to allow the cap to respond to the differential movement it will encounter without distressing the
brickwork. Figure 3 depicts a typical prefabricated cap. From this figure, general configurations and waterproofing
methods may be obtained.

Cast-in-place caps should conform to the shape and minimum dimensions shown in Fig. 3. Feathering the cap to
the edge should be avoided since this substantially reduces the thickness at the edge and therefore the potential
for deterioration is increased. Waterproofing requirements are different since shrinkage of the concrete as it cures
is a certainty. Flashing is highly recommended for cast-in-place caps. The flashing may also be considered as the
bond break material. Adequate reinforcement should be placed in the cap to help control cracking due to
shrinkage and thermal movements. Additional reinforcement may be necessary in the portion of the cap that
overhangs the face of the chimney. Figure 3 shows one method of forming a cast-in-place chimney cap.

When using a chimney cap that does not overhang the face of the chimney, the last two courses of the chimney
brickwork should be corbeled out to form a drip to help reduce the amount of water allowed to run down the face
of the chimney. The flue liner should extend a minimum of 2 in. (50 mm) above the top of the cap, see Fig. 3.

Appliance Chimneys

General. Fireplace and appliance chimneys have few dissimilarities. The general recommendations for the
construction of fireplace chimneys and the proper consideration of three additional components should produce a
functional appliance chimney. The three components, either not present in fireplace chimneys or incorporated into
the body of the fireplace are: 1) the foundation, 2) the cleanout door, and 3) the thimble.
Foundation. The foundation supports the chimney and must be sized to carry all superimposed loads. However,
most building codes disallow using the chimney walls as structural elements to support other building
components. When designing the foundation, care should be taken to account for soil conditions and type.
Undisturbed or well-compacted soil will generally be sufficient, however, some types of soil conditions may
require additional analysis.

Building codes generally require that the foundation be at least 12 in. (300 mm) thick, and, in plan view, extend a
minimum of 6 in. (150 mm) beyond each face of the masonry bearing on it. It should also penetrate the frost line
to reduce the possibility of “heaving” of the foundation while the ground is freezing.

Cleanout Door. A cleanout door may not be necessary when venting appliances that use clean burning fuels
such as natural gas, however other fuels may produce combustion by-products that will accumulate at the bottom
of the chimney and require periodic removal. The cleanout door should be of ferrous metal and set to provide as
airtight a seal as possible. If desired, the cleanout door may be oriented toward the interior of the structure,
however. the prime consideration in sizing and locating the door is the ease with which it can be used.
Thimble. A thimble is the lined opening through the chimney wall that receives the smoke pipe connector, as
shown in Fig. 10. A thimble should be set in the chimney at the location of the entrance of the pipe connector. It
should be built integrally with the chimney and made as airtight as possible, by using either boiler putty or
asbestos cement. The thimble should be set flush with the interior face of the flue liners, and at least 18 in. (460
mm) below the ceiling. The thimble should have a minimum of 8 in. (200 mm) of flue liner extending below its
lowest point, see Fig. 10.

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SUMMARY

This Technical Notes has given suggested design and construction methods for residential chimneys. Although,
there are differences, both appliance and fireplace chimneys use similar construction techniques and materials.
Since the prime function of a chimney is fire safety both quality workmanship and materials should be used.
The information and suggestions contained in this Technical Notes are based on the available data and the
experience of the Brick Industry Association’s technical staff. The recommendations and suggestions are offered
as a guide for consideration by the designers, specifiers, and owners of buildings when anticipating the design,
detailing and construction of residential chimneys. The final decision to use or not to use these recommendations
and materials in brick masonry chimneys is not within the purview of the Brick Industry Association and must rest
with the project designer, or owner.

REFERENCES

1. One and Two Family Dwelling Code, published by Building Officials and Code Administrators, Inc.,
Homewood, Illinois; International Conference of Building Officials, Whittier, California; and Southern
Building Code Congress, International, Inc., Birmingham, Alabama.
2. Book of Successful Fireplaces, How to Build, Decorate and Use Them, 20th Edition, by R. J. Lytle and
Marie-Jeanne Lytle, Structures Publishing Company, Farmington, Michigan, 1977.
3. How to Install a Fireplace, by Donald R. Brann, Direction Simplified, Inc., Briarcliff Manor, New York,
1976.
4. 1979 Equipment Volume, ASHRAE Handbook and Product Directory, by American Society of Heating,
Refrigerating and Air-Conditioning Engineers, Inc., New York, New York, 1979.

INTRODUCTION

Although some masonry walls require protective coatings to impart color and help in resisting rain penetration,
clay masonry requires no painting or surface treatment. Brick are generally selected because, among other
characteristics, they have integral and durable color and, when properly constructed, are resistant to rain
penetration.

Clay masonry walls may be painted to increase light reflection or for decorative purposes. Most paint authorities
agree that, once painted, exterior masonry will require repainting every three to five years.
This issue of Technical Notes discusses general applications of paint to interior and exterior brick walls, and a
brief discussion on specific paints suitable for brick masonry.

GENERAL

It is often erroneously assumed that brick masonry walls that are to be painted can be built with less durable
materials and, in some instances, with less than extreme care in workmanship than would normally be used for
unpainted brick walls. This is not the case. When a brick wall is to be painted, the selection of materials, both
brick units and mortar, and the workmanship used in constructing the wall should all be of the highest quality; at
least as good in quality as when the walls are to be left exposed. Every care should be taken to see that joints are
properly filled with mortar to avoid the entrance of moisture into the wall, since it may become trapped behind the
paint and cause problems. Every care should be taken to see that there are no efflorescing materials in the wall,
either in the mortar, brick units or in the backup, since efflorescence beneath the paint film can also cause
problems. See Technical Notes 23 Series.

Brick. Brick units to be used for walls that are to be painted should conform to the applicable requirements of the
ASTM Specifications for Building Brick or Facing Brick, C 62 or C 216, respectively. The grade of units (which
designates their durability) should not be lower than would be used if the wall were not to be painted. Grade SW
is recommended. It may be acceptable to use brick units which are durable but differ in color in a wall to be
painted. However, care should be taken that the units have similar absorption and suction characteristics so that
the paint applied will adhere to all of the surfaces and have a uniform acceptable appearance.
Mortar. Mortar for brick masonry walls to be painted should conform to the Specifications for Mortar for Unit
Masonry, ASTM C 270, Proportion Specifications. It is suggested that the mortar consist of portland cement and
lime, and that the mortar type be selected on the basis of the structural requirements of the wall. See Technical
Notes 8.

Paint. Paint for application to brick masonry walls should be durable, easy to apply and have good adhesive
characteristics. It should be porous if applied on exterior masonry, thereby permitting the wall to breathe and
preventing the trapping of free moisture behind the paint film.

CONSIDERATIONS FOR PAINTING CLAY MASONRY

In selecting a paint system for a brick masonry wall, the primary concern should be the characteristics of the
surface and the exposure conditions of the wall. A primer coat may be of particular importance, especially where
unusual or severe conditions exist.

Alkalinity. The chemical property of masonry which may have a significant effect on paint durability and
performance is the alkalinity of the wall. Brick are normally neutral, but are set in mortars which are chemically
basic. Paint products, which are based on drying oils, may be attacked by free alkali and the oils can become
saponified. To prevent this occurrence, an alkaline-resistant primer is recommended.

Efflorescence. The deposit of water-soluble salts on the surface of masonry, efflorescence, is another factor that
can hamper the performance of painted masonry. Efflorescence, which is present on the surface, should be
removed and, once removed, the surface should be observed for reoccurrence prior to being painted. Methods of
preventing and removing efflorescence are discussed in Technical Notes 23 Series, “Efflorescence-Causes,
Prevention and Control”.

Water and Moisture. Water or moisture in a masonry system will generally hamper the satisfactory performance
of the painted surface. Moisture may enter masonry walls in any of several ways; through the pores of the
material, through incompletely bonded or only partially filled mortar joints, copings, sills and projections, through
incomplete caulked joints and improperly installed flashing or where flashing is omitted. In general, brick wall
surfaces should be dry for painting. Acceptable moisture conditions for masonry walls to receive paint are listed in
Table 1. The use of an electrical moisture meter may be used to measure the moisture content of a wall

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SURFACE PREPARATION

General. Proper surface preparation is as important as paint selection. Because each coat is the foundation for all
future coats, success or failure depends largely upon surface preparation. Thoroughly examine all surfaces to
determine the required preparation. Previously painted surfaces often require the greatest effort. Before painting,
remove all loose matter. Take special care when cleaning surfaces for emulsion paints and primers. They are
nonpenetrating and require cleaner surfaces than solvent-based paints. Some paints can or should be applied to
damp surfaces. Others must not. Be sure to follow directions accompanying proprietary brands.

New Masonry. As a general rule, new clay masonry is seldom painted. It is difficult to justify the extra expenditure
for initial and future painting. However, if for any reason painting new masonry is desired, there are a few
precautions necessary for reasonable success.

Do not wash new clay masonry walls with acid cleaning solutions. Acid reactions can result in paint failures. Use
alkali-resistant paints. If low-alkali portland cement is not used in the mortar, it may be necessary to neutralize the
wall to reduce the possibility of alkali-caused failures. Zinc chloride or zinc sulfate solution, 2 to 3 1/2 lb per gal of
water, is often used for this purpose.

Existing Masonry. Examine older unpainted masonry for evidence of efflorescence, mildew, mold and moss.
While these conditions are not common, they all indicate the presence of moisture. Examine all possible entry
points for water. Where necessary, repair flashing and caulking; tuckpoint defective mortar joints.

Remove all efflorescence by scrubbing with clear water and a stiff brush. A wall which has effloresced for a long
time may present difficulties. The presence of moisture, the deposition of salts and the probable presence of
alkalies are all factors which may contribute to the deterioration of paints.

If moss has accumulated on damp, shaded masonry, apply an ordinary weed killer. Wet the wall with clear water
before applying weed killers to prevent them from being drawn into the wall. Chemical weed killers may contain
solubles which can contribute to efflorescence or react unfavorably with paint, and should be removed after being
used by scrubbing the wall with a stiff brush while rinsing with clear water.

Mildew seldom occurs on unpainted masonry. However, where present, treat it the same as on painted surfaces,
discussed in the following paragraphs. Be sure to wet the wall before applying any cleaning solution. Clean small
areas and rinse thoroughly. For further discussion on cleaning brick see Technical Notes 20 Revised, “Cleaning
Clay Products Masonry”.

Painted Surfaces. Previously painted surfaces normally require extensive preparation prior to repainting (refer to

Table 2 for typical paint failures). Under humid conditions, mildew may have developed. Mildew may feed on a
paint film or on particles trapped by the painted surface. If present, remove it completely before applying paint.

Otherwise, growth will continue, damaging new paint. Mildew has been successfully removed by steam cleaning
and sand blasting. The following is also effective:
3 oz trisodium phosphate (Soilax, Spic and Span, etc.), plus
1 oz detergent (Tide, All, etc.), plus
1 qt 5 per cent sodium hyperchlorite (Chlorox, Purex, etc.), plus
3 qt warm water, or enough to make 1 gal of solution.

Use this solution to remove mildew and dirt. Scrub with a medium soft brush until the surface is clean; then rinse
thoroughly with fresh water. For small areas, use an ordinary household cleanser. Scrub with a medium soft brush
and then rinse thoroughly. Use masonry paints containing a mildewcide to help prevent molds from recurring.
Remove all peeled, cracked, flaked or blistered paint by scraping, wire brushing or sand blasting. In some
instances, old paint may be burned off, but this should be done only by skilled operators. Like efflorescence, paint
blistering is caused by water within the masonry. Search for the water’s source and take the necessary corrective
measures to keep water out of the wall.

If alligatoring exists, remove the entire finish. There is no other means of correction.

If slight chalking has occurred, brush the surface thoroughly. However, if chalking is deep, remove by scrubbing
with a stiff fiber brush and a solution of trisodium phosphate and water. Rinse the surface thoroughly afterwards.

Use a penetrating primer to improve adhesion of the final coat.

Excessive paint buildup results from too many coats or excessively thick coats. Where it occurs, remove all paint
and treat as a new surface.

Completely remove cement-based paints before repainting with other types. An exception to this rule is the use of
cement-based paints as primers which will be covered by another paint within a relatively short time. If the wall
will be repainted with another cement-based paint, wire brushing and scrubbing will suffice, providing treatments
for mildew, efflorescence, etc. are not required.

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MASONRY PAINTS

Because all paints have distinct properties and because surfaces vary considerably, even the most experienced
painting contractors carefully examine a surface before making recommendations. However, the following will
generally indicate the proper use of masonry paints.

CEMENT-BASED PAINTS

For many years, cement-based paints have been satisfactory coatings for masonry surfaces. They achieved
popularity because they have relatively good adherence and tendency to make a wall less permeable to free
water. Cement-based paints are permeable, permitting the wall to breathe. Their main components are portland
cement, lime and pigments. Additives, binders and sands may be added.

Although cement-based paints are more difficult to apply than other types, good surface protection results when
properly applied. While they are not complete waterproofers, cement-based paints help to seal and fill porous
areas, excluding large amounts of free water. White and light colors tend to be the most satisfactory. It is difficult
to obtain a uniform coating with darker shades. Lighter colors tend to become translucent when wet, and dark
colors become darker. Color returns to normal as the wall surface dries. Cement-based paints can provide a good
base for other paints applied within a relatively short time.

The following procedure for applying paint on a properly prepared surface generally applies:
1. Cure new masonry walls for approximately one month before applying cement-based paints.
2. Dampen wall surfaces thoroughly by spraying with water.
3. Cement-based paints are packaged in powdered form. Because their cementitious components begin to
hydrate upon contact with water, mix immediately prior to application for optimum results.
4. Apply heavy coats with a stiff brush, allowing at least 24 hr to elapse between coats.
5. During this time, keep the wall damp by periodically spraying it with water.
6. Apply additional coats in the same manner.
7. Keep the final coat damp for several days to properly cure.

WATER-THINNED EMULSION PAINTS

General Characteristics. Water-thinned emulsion paints, commonly referred to as latex paints, are relatively
easy to apply. Water-thinned emulsions may be brush, roller or spray-applied. However, brush application is
preferable, especially on coarse-textured masonry. Emulsion paints dry quickly, have practically no odor and
present no fire hazard. They may be applied to damp surfaces, permitting painting shortly after a rain or on walls
damp with condensation.

As a group, these paints are alkali-resistant. Hence, neutralizing washes and curing periods are not usually
necessary before painting. Water emulsion paints possess high water vapor permeability and are known to have
performed well on brick substrates that have been properly prepared.

Emulsion paints will not adhere well to moderately chalky surfaces. If possible, repainting should be done before
the previous coat chalks excessively. However, specifically formulated latex paints are available containing
emulsified oils or emulsified alkyds which facilitate wetting of chalky surfaces. This property enables the paint to
bond the chalk together and to the substrate.

The principal water-thinned emulsion paint types are: butadiene-styrene, vinyl, acrylic, alkyd and multicolored
lacquers.

Butadiene-Styrene Paints. These relatively low-cost, rubber-based latex paints develop water resistance more
slowly than vinyl or acrylic emulsions. They are most satisfactory in light tints as chalking rate may be excessive
in deep colors.

Vinyl Paints. Polyvinyl acetate emulsion paints dry faster, have improved color retention and a more uniform,
lower sheen than rubber-based latex paints.

Acrylic Emulsion Paints. Acrylic emulsions have excellent color retention, permit recoating in 30 min or less,
and have good alkali resistance. Acrylics have high resistance to water spotting and may be scrubbed easily.
Alkyd Emulsion Paints. Alkyd emulsions are related to solvent-thinned alkyd types, but have all the general
characteristics of latex paints. They do have more penetration than most water-thinned emulsions, achieving
better adhesion on chalky surfaces. Compared to other emulsion paints, these are rather slow to dry, have more
odor, are not as resistant to alkalies, and have poorer color retention. Under normal exposure conditions, alkyd
emulsions can serve as a finished coat over a suitable primer.

Multicolored Lacquers. A specialized paint group, multicolored lacquers are applied only by spray gun. The
finished film appears as a base color with separate dots or particles of contrasting colors. These paints will cover
many surface defects and irregularities. However, they must be applied over a base coat of another type; for
example, polyvinyl acetate or acrylic emulsion paints.

FILL COATS

Fill coats are base coats for exterior masonry. They are similar in composition, application and uses to cementbased paints. However, fill coats contain an emulsion paint in place of some water, giving improved adhesion and
a tougher film than unmodified cement paints. Fill coats have greater water retention, giving the cement a better
chance to cure. This is particularly valuable in arid areas where it is difficult to keep the painted surface moist
during the curing period.

SOLVENT-THINNED PAINTS

The five major solvent-thinned paints are oil-based, alkyd (synthetic resin), synthetic rubber, chlorinated rubber
and epoxy. Oil-based and alkyd paints are not recommended for exterior masonry. Solvent-thinned paints should
be applied only to completely dry, clean surfaces. They produce relatively nonporous films and should be used
only on interior masonry walls not susceptible to moisture penetration. The exception to this is special purpose
paint, such as synthetic rubber, chlorinated rubber and epoxy paints.

Oil-Based Paints. Oil-based paints have been used for many years. They are relatively non-porous and
recommended for interior use only. Although several coats may be required for uniform color and good
appearance, they bind well to porous masonry. As with most solvent-based paints, they have good penetration on
relatively chalky surfaces, but are highly susceptible to alkalies. New masonry must be thoroughly neutralized to
avoid saponification. Available in a wide color range, oil-based paints are moderately easy to apply. Several days’
drying is generally required between coats.

Alkyd Paints. Alkyd paints are similar to oil-based paints in most general characteristics. They may have slightly
less penetration, resulting in somewhat better color uniformity at the cost of adhering power. Alkyd paints are
more difficult to brush, dry faster and give a harder film than oil-based paints. These, too, are nonpermeable and
are recommended for interior use only.

Synthetic Rubber and Chlorinated Rubber Paints. These paints have excellent penetration and good adhesion
to previously painted, moderately chalky surfaces as well as new surfaces. They are reported to be more resistant
to efflorescence and are generally good in alkali resistance. They may be applied directly to alkaline masonry
surfaces, but are more difficult to brush on than oil paints. Darker colored synthetic rubber paints lack color
uniformity. Both types have high resistance to corrosive fumes and chemicals. For this reason, they are often
specified for industrial applications. Both types require very strong volatile solvents, a fire hazard which may prove
undesirable.

Epoxy Paints. Epoxy paints are of synthetic resins generally composed of two parts, a resin base and a liquid
activator. They must be used within a relatively short time after mixing. Epoxies can be applied over alkaline
surfaces, have very good adhering power, and good corrosion and fume resistance. However, some types chalk
excessively if used outdoors. Epoxies are relatively expensive and somewhat difficult to apply.

“HIGH-BUILD” PAINT COATINGS

High-build paint coatings are generally used on interiors to give the effect of glazed brick. Some coatings are
based on two-component urethane polyesters and epoxies. Others are of an emulsion-based coat with acrylic
lacquer. These paint systems usually include fillers to smooth out surface irregularities.

OTHER COATINGS

Heavily applied coatings of the so-called “breathing type” are available with either a water or solvent base. They
are generally composed of asbestos fiber and sand, and applied thickly to hide minor surface imperfections. The
presence of moisture on the surface of a masonry wall generally will not harm the latex type. Lower application
temperatures of 35 F to 50 F on the other hand are less damaging to the solvent type.
For both types, adhesion is mostly mechanical because of low binder and high pigment content. Some coatings
require special primers to insure adhesion. Although these coatings are reported to have given good performance
on masonry, they tend to show stains where water runoff occurs.
These coatings are capable of allowing passage of water vapor, but cannot transmit large quantities of water that
may enter through construction defects. Failure may occur as a result of freezing of water accumulation behind
the film.

PAINTING NEAR UNPAINTED MASONRY

Often windows and trim of masonry buildings are painted with self-cleaning paints to keep surfaces fresh and
clean. Unfortunately, self-cleaning is generally achieved through chalking. The theory is that rain will wash away
chalked paint, constantly exposing a fresh paint surface. The theory works well, but too often no provision is made
to keep chalk-contaminated rain water away from masonry surfaces. The result is usually more unsightly than
dirty paint on trim or windows. Avoid this staining by choosing nonchalking paints for windows and trim and by
providing a means of draining water away from wall surfaces.

REFERENCES

1. Manual on the Selection and Use of Paints, Technical Report #6, National Research Council of
Canada, Division of Building Research, 1950, Ottawa, Canada.
2. Paints for Exterior Masonry Walls, BMS110, National Bureau of Standards, 1947, Washington, D.C.
3. Field Applied Paints and Coatings, Publication 653, Building Research Institute, 1959, Washington,
D.C.
4. Paints and Coatings, Publication 706, Building Research Institute, 1960, Washington, D.C.
5. Painting Walls; 1, Building Research Station Digest (2nd Series), No. 55, Building Research Station,
1965, Garston, Herts., England.
6. Coatings for Masonry Surfaces, by H. E. Ashton, Canadian Building Digest, CBD 131, November 1970,
Ottawa, Canada.
7. Coatings for Masonry and Cementitious Materials, by Walter Bayer, Construction Specifier, November

This Technical Notes provides a review of the national masonry design standard, ACI 530/ASCE
5/TMS 402, and its accompanying masonry specification, ACI 530.1/ASCE 6/TMS 602. New provisions
and revisions of existing standards for masonry design are emphasized. Subjects discussed pertaining to
the design standard are: allowable stress and strength design of unreinforced and reinforced masonry,
prestressed masonry, empirical design, glass block masonry, masonry veneer, quality assurance, and
seismic provisions. Items addressed for the masonry specification are: requirements checklist and
submittals, masonry quality assurance and inspection requirements, reinforcement and metal accessories,
erection tolerances, construction procedures and grouting requirements.

Key Words: adhered veneer, allowable stress design, anchored veneer, building code, design standard,
empirical design, inspection, prestressed masonry, specification, strength design.

INTRODUCTION

The American Concrete Institute (ACI), American Society of Civil Engineers (ASCE), and The Masonry
Society (TMS) promulgate a national consensus standard for the structural design of masonry elements
and a standard specification for masonry construction. These standards are titled the Building Code
Requirements for Masonry Structures (ACI 530/ASCE 5/TMS 402) and the Specification for Masonry
Structures (ACI 530.1/ASCE 6/TMS 602). They were developed to consolidate and advance existing
standards for the design and construction of masonry.

This Technical Notes, the first in a series, discusses various sections of the Building Code Requirements
for Masonry Structures and the Specification for Masonry Structures in brief detail. Emphasis is placed on
the new requirements in the 2002 edition of the standards. Changes from prior masonry standards dealing
with the design of brick masonry structures are also presented. Other Technical Notes in this series
provide material and section properties of brick masonry members and more extensive discussion of the
requirements of these standards. For more information about the requirements of these standards and
examples of their application, the reader is referred to the Masonry Designer’s Guide (MDG). The MDG is
published by The Masonry Society and contains an extensive number of design examples that illustrate the
proper application of the MSJC Code and Specification requirements.

In this Technical Notes, the Building Code Requirements for Masonry Structures and the Specification for
Masonry Structures are referred to as the Masonry Standards Joint Committee (MSJC) Code and
Specification, respectively. The pertinent section and article numbers from the MSJC Code and
Specification, are stated in parentheses following the discussion of particular topics for quick reference.

HISTORY AND DEVELOPMENT

The development of this single masonry standard for the design and construction industry began in 1977.
At that time, there were several design standards for masonry. These standards did not have consistent
requirements. It was difficult for engineers and architects to select the appropriate design criteria for
masonry elements. Concerned individuals representing masonry materials and the design profession saw
the need for a single, national consensus standard for the design and construction of all types of masonry.
In 1977, ACI and ASCE agreed to jointly develop a consensus standard for masonry design with the
support of the masonry industry. The MSJC was formed with a balanced membership of building officials,
contractors, university professors, consultants, material producers and designers who are members of ACI
or ASCE. The Masonry Society joined as a sponsoring organization in 1991. Currently, the MSJC is
comprised of over eighty regular (voting) and forty associate members. The MSJC Code and Specification
are available from each of the sponsoring organizations or from the Brick Industry Association.
Changes to the MSJC Code and Specification are written, balloted and approved within the MSJC. A
review by the sponsoring organizations’ technical activity committees follows. In order to obtain a national
consensus, the approved draft undergoes a public review. Approval by the MSJC of the first edition of the
MSJC Code and Specification occurred in June 1986. Public review began in 1988 with the final approval
of the 1988 MSJC Code and Specification in August 1989.

Commentaries for the MSJC Code and Specification were also developed. These documents provide
background information on the design and specification provisions. Considerations of the MSJC members
in determining requirements and references to research papers and articles are included in the
commentaries for further information.

The MSJC Code, Specification and Commentaries are revised on a three- or four-year cycle. The first
revision was issued in 1992. Most of the changes were editorial in nature or clarified intent or omissions.
In 1995 new chapters on glass unit masonry and anchored masonry veneers were added, and the MSJC
Specification was reformatted. Metric conversions were added throughout the standards in accordance
with the metrication policy of ASCE in addition to an index of key words. The 1999 edition includes a
number of significant changes. The MSJC Code and its Commentary were reformatted. A chapter on
prestressed masonry, a section on adhered veneer and a quality assurance program were added. Other
changes in the MSJC Code and Specification include new design values for elastic moduli and masonry
compressive strength and the inclusion of mortar cement. In the 2002 edition there were significant
changes to the seismic design provisions, with prescriptive requirements for specific shear wall types. A
chapter on strength design was added. Other minor changes are documented in this Technical Notes.

Building Code Acceptance

The MSJC Code is to be adopted by a model building code and, subsequently, by a local jurisdiction. State
and local building code committees are encouraged to adopt the model building codes which include the
MSJC Code for the design of masonry. With adoption of the MSJC Code, the Specification is automatically
adopted because the MSJC Code requires that materials and construction comply with the MSJC
Specification. The local jurisdiction has the responsibility for enforcement and compliance of masonry
construction to the MSJC Specification once it is adopted.

Two of the previous model building code organizations, the Standard Building Code Congress International
(SBCCI) and the Building Officials and Code Administrators (BOCA), chose to include the MSJC Code in
their documents. This adoption by reference began in 1988 and1989, respectively. The International
Council of Building Officials (ICBO) chose to maintain masonry design criteria within the Uniform Building
Code itself, rather than adopting the MSJC standards by reference. However, many of the masonry design
and construction requirements of the Uniform Building Code have been changed over the last several years
to be consistent with the requirements of the MSJC Code and Specification.

The International Code Council (ICC) was formed by the three existing code organizations (SBCCI),
(BOCA) and (ICBO) with the charge to produce a single set of codes, referred to as the I-codes. Two Icodes that are important to the brick industry are the International Building Code (IBC) and International

Residential Code (IRC). The National Fire Protection Association (NFPA) is also developing another
building code called NFPA 5000. The I-codes and NFPA 5000 reference the 2002 MSJC Code.

Benefits

The MSJC Code and Specification have had positive results; the design and construction community has
become more confident with their use. Designers have one national standard that covers nearly all types of
masonry construction. Architects are able to prepare and submit complete, concise specifications more
easily. Contractors have more consistent and better quality specifications for projects. Owners obtain
more uniform quality of masonry. Other benefits presented by the MSJC Code and Specification are:

1. Nearly all forms of masonry are covered, including unreinforced, reinforced and prestressed
masonry, glass unit masonry, and adhered and anchored veneer masonry.

2. Requirements for all masonry materials are covered, including clay and shale brick, concrete block,
stone, glass unit, mortar, grout and metal accessories.

3. Differences in material properties are recognized and quantified.

4. The same rational design procedures are utilized for clay and concrete masonry.

5. Responsibilities and duties of the owner, designer, testing agency, and contractor are clearly
established.

6. Quality assurance and inspection requirements are included.

7. Design, materials and testing are the decision of the architect or engineer.

8. Contract administration is easier.

Since the introduction of the MSJC standards in 1988, there has been a shift in the masonry design and
construction communities. Designers and contractors use the MSJC Code and Specification with more
frequency. Indicative of this growth, the MSJC Code is now a required reference for the Professional
Engineer’s Principles and Practice examination. The MSJC Specification has placed greater demands on
the masonry contractor with the use of masonry as a structural material. Many requirements are
performance related, which may require more site inspection for verification of compliance. These
demands are advantageous and vital to the development of confidence that the masonry strengths
assumed by the designer are met by the constructed masonry.

THE MSJC CODE (ACI 530/ASCE 5/TMS 402)

The MSJC Code is the basis for masonry design by the architect or engineer. The provisions of the MSJC
Code will dictate the size and shape of masonry walls, beams, pilasters and columns. Further, it influences
the masonry materials the designer will require in the project specification. It consists of seven chapters,
which are listed below.

Chapter 1 – General Design Requirements for Masonry

Chapter 2 – Allowable Stress Design

Chapter 3 – Strength Design of Masonry (New Chapter)

Chapter 4 – Prestressed Masonry

Chapter 5 – Empirical Design of Masonry

Chapter 6 – Veneer

Chapter 7 – Glass Unit Masonry

Some relevant sections of the codes are discussed in this Technical Notes and are indicated in
parentheses for each of the chapters.

Chapter 1 – General Design Requirements for Masonry

Chapter 1 contains the scope of the minimum requirements for the design of any masonry element. In this
chapter, it states that the MSJC Code supplements the model building code enforced in a jurisdiction.
When the MSJC Code conflicts with the local building code, the local building code governs. (1.1)
Project drawings and specifications must identify the individual responsible for their preparation. Items
required by the MSJC Code must be clearly marked such as: loads used in design, specified compressive
strength of masonry, reinforcement, anchors and ties with size and spacing, size and location of all
structural elements, provisions for differential movement, and size and location of conduit, pipes and
sleeves. Contract documents must include a quality assurance program. (1.2)

The MSJC Code permits alternative design methods from those stated in the MSJC Code. This is to
recognize new applications of masonry and different structural analysis techniques. (1.3)

Chapter 1 also includes the notation and definitions contained within the MSJC Code. Capital letters are
used for permitted stresses and lower case letters are used for calculated or applied stresses. (1.5) For
example, Fa is the notation for the allowable compressive stress due to axial load, while fa denotes the
calculated compressive stress due to axial load. The definitions are specifically related to their meaning as
used in the MSJC Code. Definitions in the MSJC Code are coordinated with those in the MSJC
Specification. Definitions of terms relating to strength design of masonry and for prestressed masonry have
been added. (1.6)

The following are brief summaries, highlights, of several sections within Chapter 1.

Section 1.7 – Loading. Service loads are used as the basis of design and are governed by the building
code that adopts the MSJC Code. If a building code is not enforced in the area under consideration, then
the MSJC Code requires that the load provisions of the 1993 edition of ASCE 7 Design Loads for Buildings
and Other Structures apply to masonry structures. Allowable stresses given in the MSJC Code are based
on failure stresses with a factor of safety in the range of 2 to 5. The structural system must resist wind and
earthquake loads and accommodate the resulting deformations. (1.7.3) The effects of restraint of
movement due to prestressing, vibrations, impact, shrinkage, expansion, temperature changes, creep,
unequal settlement of supports and differential movement must also be considered in design. (1.7.4)

Section 1.8 – Material Properties. Material properties are included for both clay and concrete masonry.
The MSJC Code and Specification was the first national masonry standard to state design coefficients for
thermal expansion, moisture expansion, shrinkage and creep. For design computations, the amount of
shrinkage of brick masonry is taken as zero. The moduli of elasticity, Em, of clay and concrete masonry is
no longer based on the net area compressive strength of the brick and the type of mortar used in
construction. Em is now directly related to the specified compressive strength of masonry, f’m. For clay
masonry, Em is equal to 700 times f’m. Alternately, Em may be determined by the chord modulus of
elasticity taken between 0.05 and 0.33 of the maximum compressive strength of each prism determined by
test in accordance with Article 1.4 B.3 of the MSJC Specification. Refer to Technical Notes 18 Series for
an extensive discussion of differential movement of brick masonry elements. (1.8.2.2)

Section 1.9 – Section Properties. Section properties are used to determine stress computations.
Computations for stiffness, radius of gyration and flange design for intersecting walls are based on the
minimum net area of the section. This is normally the mortar-bedded area. When different materials are
combined in a single element, the transformed area must be used to account for differences in elastic
moduli of the dissimilar materials. Radius of gyration of the section, rather than the minimum thickness, is
used to determine the slenderness reduction for members in compression. (1.9)

Section 1.10 – Deflection. Deflection limits are imposed for beams and lintels that support unreinforced
masonry. The deflection should not exceed the span length divided by 600 or 0.3 in. (7.6 mm). Deflection
of the masonry member should be calculated based upon uncracked section properties. (1.10, 1.9.2)

Section 1.11 – Stack Bond Masonry. The MSJC Code requires that stack bond masonry be reinforced with
a prescriptive amount of horizontal reinforcement. This may be placed as joint reinforcement or in bond
beams spaced not more than 48 in. (1.2 m) on center vertically. (1.11)

Section 1.12 – Details of Reinforcement. The reinforcement detailing requirements given in this chapter
are similar to those for reinforced concrete under ACI 318, Building Code Requirements for Reinforced
Concrete. The maximum size of reinforcing bar permitted in masonry members, designed by the allowable
stress or empirical design methods, is a No. 11 (M #36) bar. Horizontal joint reinforcement is permitted as
structural reinforcement for the same design methods. Placement limits for reinforcement include minimum
grout spaces between the bars and masonry units of 1/4 in. (6.4 mm) and 1/2 in. (12.7 mm) for fine and
coarse grout, respectively. (1.12.2 – 1.12.3)

This section contains protection requirements for reinforcing steel. A minimum amount of masonry cover is
required, depending upon the exposure conditions. Corrosion protection is required for joint reinforcement,
wall ties, anchors and inserts in exterior walls. (1.12.4)

Minimum development lengths are stated for reinforcement. A 50 percent increase is recommended for
epoxy coated bars. (2.1.10.2) Standard hooks, minimum bend diameters, and splice requirements are
consistent with those for reinforced concrete members. (1.12.5, 1.12.6) Chapter 3 contains variations in
some of these requirements when strength design is used.

Section 1.13 – Seismic Design Requirements. These requirements apply to the design and construction of
all masonry, except glass unit masonry and masonry veneers, for all Seismic Design Categories (SDC) as
defined in ASCE 7-98. Early editions of the MSJC included seismic design information as optional
information in the Appendix and based the requirements on Seismic Zones. Since 1995, the seismic
requirements are mandatory parts of the Code. Seismic provisions for masonry veneers are found in

Chapter 6, Veneers.

Special seismic requirements in Section 1.13 are invoked by SDC. The requirements are additive for each
higher SDC. For example, buildings in category D must meet all the requirements for buildings in
categories A, B and C, plus the additional requirements stated in Section 1.13 for buildings in category D.
Five types of shear walls that serve as the lateral force-resisting system are described. Each has a
required design method and prescriptive reinforcement requirements, see Table 1. Their use is permitted
by the seismic design category applicable to the structure under design.

In category A, the provisions of Chapters 2, 3, 4, or 5 of the MSJC Code apply. There is a calculated story
drift limit of 0.007 times the story height. Anchorage of masonry walls must meet a minimum design force
of 1000 times the effective peak velocity-related acceleration. (1.13.3)

For buildings in category B, the lateral force-resisting system must comply with the requirements of Chapter
2, 3, or 4 of the MSJC Code. It cannot be designed in accordance with the empirical requirements of
Chapter 5. The lateral force-resisting system includes structural masonry members such as columns,
beams and shear walls. It does not include non-loadbearing elements, such as partition walls. (1.13.4)
Masonry buildings in category C must meet more stringent requirements. Members that are not part of the
main lateral force-resisting system must be isolated so that they do not adversely affect the response of the
lateral force-resisting system. Connections are strengthened and minimum amounts of reinforcement are
required for shear walls and non-loadbearing masonry members in order to provide more ductility to the
structure. (1.13.5) Partition walls, screen walls and other elements that are not designed to resist vertical
or lateral loads other than their own weight must be isolated from receiving these loads and designed to
accommodate drift.

The special seismic provisions for categories D and E are still more restrictive. Minimum reinforcement
requirements are increased for all members. Type N mortar and masonry cement mortars are not
permitted for the lateral force-resisting system. (1.13.6, 1.13.7)

Section 1.14 – Quality Assurance. This section defines a quality assurance program with different
requirements based on the type of facility and method of design. Minimum tests, submittals and inspection
requirements are defined for three levels of quality assurance. (1.14.1)
The quality assurance program must include procedures for reporting, review and resolution of
noncompliances. (1.14.5) Qualifications for testing laboratories and for inspection agencies must also be
defined. (1.14.6)

The quality assurance program requires that each wythe of masonry and the grout, if present, must meet or
exceed the specified compressive strength of masonry, f’m. Compressive strength of masonry must be
verified in accordance with the provisions of the MSJC Specification. (1.14.2)

Section 1.15 – Construction. Construction of masonry must comply with the MSJC Specification.
Requirements for grouting are introduced in Section 1.15. The type of grout, either fine or coarse,
determines the minimum grout space dimensions and maximum grout pour height permitted. New in the
2002 edition is the inclusion of a grout demonstration panel. The limits can be exceeded if the panel
indicates that the spaces are filled and adequately consolidated. Grout must attain a minimum
compressive strength of 2000 psi (13.8 MPa) at 28 days. (Table 1.15.1)
In addition, Section 1.15 contains provisions for pipes and conduits embedded in masonry elements. The
effect on structural performance of the opening caused by the embedded item must be considered.
Limitations on location, size, relative area and materials contained within pipes and conduit are included.
(1.15.2)

Chapter 2 – Allowable Stress Design

Allowable stress design (ASD) methodology has been used in masonry design for many years. The ASD
provisions of the MSJC Code are the most advanced to date for masonry members and are reflective of the
extensive amount of research and experience gained over the last century.
Chapter 2 of the MSJC Code states general provisions and establishes the scope of the rational design
requirements. The rational design provisions are based upon a few assumptions inherent in the ASD
approach, which are as follows:

1. Masonry materials are linearly elastic under service loads (materials rebound to original position
when unloaded, rather than deforming permanently).

2. Stress is directly proportional to strain (applied load is directly proportional to displacement).

3. Masonry materials behave homogeneously (brick, mortar and grout behave as one element rather
than separately).

4. Sections plane before bending remain plane after bending (flexural members do not warp).
Service loads are used as the basis of allowable stress design. Allowable stresses given in the MSJC
Code are based on failure stresses with a factor of safety in the range of 2 to 5. Section 2.1.2 contains the
loading combinations to be used for allowable stress design. For moment strength design under Section
4.5.3.3.2, factored loads shall be combined as required by the general building code. When the general
building code does not provide load combinations, structures or members shall use the most restrictive
combinations of loads. (2.1.2)

The specified compressive strength of masonry, f’m, must be determined by the designer and clearly stated
in the contract documents. The specified compressive strength must be verified by the contractor as
required by the methods stipulated in the MSJC Specification. (2.1.3)

Anchor bolts consist of plate, headed and bent bar assemblies. Allowable loads for tension, shear and
combined tension and shear are given. Provisions for minimum embedment length are provided to ensure
proper transfer of load between the masonry and the anchor bolt. (2.1.4) Refer to Technical Notes 44 for
further discussion of the design of anchor bolts.

The MSJC Code requirements differentiate between multiwythe walls with respect to composite or noncomposite action. Composite action requires a rigid transfer of stress between wythes so that the wythes
act as a single element in resisting loads. The wythes must be bonded with a filled collar joint and metal
ties or with masonry headers. Prescriptive size and spacing limitations for metal wall ties are taken from
previous masonry standards. For multiwythe, composite walls, criteria for allowable shear stresses at the
interface between a wythe and a collar joint have been introduced that were not included in previous
masonry standards. These allowable shear stresses are: a) 5 psi (34.5 kPa) for mortared collar joints, b)
10 psi (69.0 kPa) for grouted collar joints, and c) the square root of the unit compressive strength of the
header. (2.1.5.2.2)

When non-composite action occurs, each wythe is designed to individually resist the effects of imposed
loads. Loads are apportioned to wythes based upon their relative stiffnesses. As with composite walls,
prescriptive requirements for metal wall ties are based on past experience. (2.1.5.3 ) Wall ties with drips
are now prohibited.

Columns are isolated vertical members whose horizontal dimension at right angles to the thickness does
not exceed 3 times its thickness. Also, the member’s height must be at least 3 times its thickness. The
minimum dimension of a column is 8 in. (203 mm) and the maximum ratio of effective height to least
nominal dimension (slenderness ratio) of a column is 25. Columns must contain a minimum of four vertical
reinforcing bars and a minimum amount of lateral ties. (2.1.6)

Pilasters are thickened elements of a wall which provide resistance to lateral loads or a combination of axial
and lateral loads. Design procedures consider the pilaster and wall to act integrally, provided the two are
properly bonded. Vertical reinforcement that is intended to resist axial loads must be laterally tied in the
same manner that is required for columns. (2.1.7)

Concentrated loads must be distributed over a prescribed length of wall. Requirements depend on bond
pattern, presence of bond beams and the width of the wall. The allowable bearing stress is one-fourth of
the specified compressive strength of masonry, but may be increased for smaller bearing areas. (2.1.9)
Provisions for development of reinforcement are included. (2.1.10) Bars, hooks, welded wire fabric, and
splices are covered.

Section 2.2 – Unreinforced Masonry. Section 2.2 covers requirements for the design of masonry structures
in which tensile stresses in masonry are taken into consideration. This is known as unreinforced (plain)
masonry. Such members may, in fact, contain reinforcement for shrinkage or other reasons, but this
reinforcement is neglected in the structural design process.

The allowable axial compressive stress equation uses a different slenderness reduction factor from that
used in earlier masonry standards. The factor is a function of the radius of gyration of the member’s cross
section, rather than its thickness. Additionally, the factor of safety changed from 5 in previous masonry
standards to 4 in the MSJC Code. Unlike previous masonry design standards, the MSJC Code does not
place an arbitrary limit on the slenderness ratio of walls. Rather, the slenderness reduction factor becomes
very small for more slender walls. An equation limiting the applied axial load to one-quarter of a modified
Euler buckling load is included. The classic Euler buckling load has been modified to reflect a member with
negligible tensile strength. The unity equation has been used to limit the combination of bending and axial
load in masonry design for many years. (2.2.3, 2.3.3)

Variables affecting flexural tension of masonry include the plane on which the stress acts, mortar materials,
unit cross-section, and presence of grout. The allowable flexural tension stresses for grouted masonry
normal to bed joints were modified in the 2002 edition. (2.2.3.2)

Allowable shear stresses are based upon a parabolic shear stress distribution rather than an average shear
stress distribution, as used in previous masonry standards. Consequently, allowable shear stresses are
approximately 1.5 times those in previous masonry standards. Four allowable shear stresses for in-plane
shear must be evaluated. No allowable shear stress values are given for out-of-plane shear, but typically
these same values for in-place shear are applied. (2.2.5)

Section 2.3 – Reinforced Masonry. Section 2.3 contains requirements for the allowable stress design of
masonry elements neglecting the tensile strength of masonry. This is commonly termed reinforced
masonry. In this procedure, steel reinforcement is used to resist all tensile forces. Reinforcement may also
be required to resist shear forces. The MSJC Code does not prescribe a minimum amount of
reinforcement, except for masonry columns and for buildings in Seismic Design Categories as given in
Chapter 1. The size and placement of compressive, flexural and shear reinforcement is determined by
design requirements. (2.3.1) Allowable steel stresses are taken from previous masonry standards.

Reinforcement used to resist compressive stresses must be laterally tied. (2.3.2.2)

When the applied shear stress exceeds the given allowable shear stress for reinforced masonry without
shear reinforcement, shear reinforcement is required. For reinforced masonry containing shear
reinforcement, allowable shear stresses are increased by a factor of 3.0 for flexural members and 1.5 for
shear walls. To use the increased allowable shear stresses, shear reinforcement must be provided to
resist 100 percent of the shear force. (2.3.5)

Chapter 3 – Strength Design of Masonry

This chapter is new in the 2002 edition of the MSJC Code. This chapter was developed from research
funded by the National Science Foundation and the masonry industry.

Strength design identifies the possible failure modes that the masonry element can exhibit. By performing
this type of analysis the engineer can preclude an undesirable failure. Strength design provides for design
of inelastic performance of masonry. The loads and stresses considered are similar to those used in
allowable stress design, but service level loads are replaced with strength design loads and allowable
stresses are replaced with nominal values based on research. The required strength of the masonry must
be greater than its nominal strength multiplied by a strength reduction factor, Ø. The strength reduction
factors selected are similar to those used in concrete.

Strength design of masonry shall comply with the minimum requirements of this chapter. In addition, the
requirements of Chapter 1, Section 3.1, and either Section 3.2 or 3.3 also apply. (3.1.1) The strength
requirements are in accordance with the legally adopted building code. When this information is not
defined in the building code then the requirements of ASCE 7-98 govern. (3.1.2) Notations and definitions
used in strength design are found in Sections 1.5 and 1.6, respectively.

The remainder of Chapter 3 covers design strength (3.1.3), strength reduction factors (3.1.4), deformation
requirements (3.1.5), headed and bent-bar anchor bolts (3.1.6), material properties (3.1.7), reinforced
masonry (3.2), and unreinforced (plain) masonry (3.3). Design equations are similar to those for allowable
stress design when possible. Perhaps the most significant difference is in the development length. The
strength design formula includes cover, bar size, and masonry specified compressive strength as
variables. This formula also applies to splices.

This chapter includes maximum reinforcement ratios chosen to prevent brittle failure of shear walls. These
are applied with specific limits on strain in the masonry and steel. There are also dimensional limits for
beams, piers, and columns.

It must be pointed out that Strength Design of Masonry may not be practical in many situations and may in
fact not provide the results a designer may seek.

Chapter 4 – Prestressed Masonry

Prestressed masonry is used to eliminate tensile stresses in masonry due to externally applied loads. A
controlled amount of precompression is applied to the masonry to offset the tensile forces created under
service loads. The use of prestressing is well documented in concrete design and construction; however its
use in masonry construction in the United States is limited. The United Kingdom has a history of
successful prestressed masonry construction for over two decades.

The equipment for prestressed masonry is similar to that used in concrete construction. Some proprietary
systems have been developed specifically for use in prestressed masonry. Types of structures that have
utilized prestressed masonry in the United States include freestanding walls, such as fences, bearing walls
and masonry veneers designed to span between columns, rather than span floor-to-floor.
Prestressing tendons placed in openings in the masonry may be grouted or ungrouted. The tendons may
be pre-tensioned or post-tensioned. Pre-tensioned tendons are stressed against external abutments prior
to placing the masonry. Post-tensioned tendons are stressed against the masonry after it has been
placed. Most construction applications to date have been post-tensioned, ungrouted masonry because of
the ease of construction and overall economy. As a result, the MSJC Code focuses primarily on posttensioned masonry.

Chapter 4 provides minimum requirements for the design of structures that are prestressed with bonded or
unbonded prestressing tendons. The general design requirements found in Chapter 1, including seismic
provisions, apply to prestressed masonry with a few modifications. (4.1) Prestressed members are
designed using elastic analysis and allowable stress design. A new term, f’mi, is defined as the specified
compressive strength of masonry at the time of transfer of the prestress force. (4.2)
The remainder of Chapter 4 covers permissible stresses in the prestressing tendons, effective prestress,
axial compression and flexure, axial tension, shear, deflection, prestressing tendon anchorages, couplers,
end blocks, protection of prestressing tendons and accessories, and development of bonded tendons.

Chapter 5 – Empirical Design of Masonry

Chapter 5 presents empirical requirements for masonry structures. These requirements are based on past
proven performance. Configuration of masonry structures for compliance with empirical limits is a
technique that predates rational design methods. The empirical provisions of previous masonry standards
have been modified and advanced in Chapter 5 to reflect contemporary construction materials and
methods. The requirements are essentially unchanged from the 1999 edition.

The empirical requirements in Chapter 5 may be applied to the following masonry elements:

1. The lateral force-resisting system for buildings in Seismic Design Categories (SDC) A, and for
other building elements in SDC A through C, as defined in ASCE 7-98. (5.1.2)

2. Buildings subject to basic wind speed of 110 mph (145 km/hr) or less as defined by the ASCE 7-98
standard. (5.1.2.2)

3. Buildings not exceeding 35 ft (10.67 m) when the masonry walls are part of the main lateral forceresisting system. (5.2)
The empirical requirements may not be applied to structures resisting horizontal loads other than those due
to wind or seismic events, except that foundation walls may be as permitted in Section 5.6.3. The empirical
requirements for foundation walls include limits on the height of backfill. There are a number of restrictions
on the backfill soil and the configuration of cross walls. (5.6.3.1) The 2002 Code also requires foundation
piers to be a minimum of 8 in. (203 mm) in thickness. (5.6.4) The empirical requirements of the MSJC
Code are discussed in Technical Notes 42 Revised.

Chapter 6 – Veneers.

The requirements of Chapter 6 apply to masonry veneers. In the 2002 MSJC Code, provisions address
anchored masonry veneer and adhered masonry veneer. The requirements of this chapter are especially
important to the brick industry as the majority of brick produced in the United States is used as veneer.
Section 6.2 – Anchored veneer. The majority of this chapter contains prescriptive requirements for masonry veneer, but alternative design methods are permitted. (6.2.1) The prescriptive requirements cannot be
used in areas where the wind speed exceeds 110 mph (145 km/hr) as given in ASCE 7-98. (6.2.2.1) Many
of the requirements are based upon those found in Technical Notes 28 Series on brick veneer walls and
Technical Notes 44B on wall ties. (6.2.2.3-6.2.2.9) Seismic requirements are included for buildings in SDC
C, D, and E. (6.2.2.10)

Section 6.3 – Adhered veneer. Adhered veneer can be designed by the prescriptive requirements
contained in this section or by alternative design methods. (6.3.1) Prescriptive requirements found in the
2002 MSJC Code are based on similar requirements that have been used in the Uniform Building Code for
over 30 years. These requirements limit unit size to no more than 2 5/8 in. (66.7 mm) in specified
thickness, 36 in. (914 mm) in any face dimension and 5 ft2 (0.46 m2
) in total face area. The weight of
adhered veneer units is limited to15 lbs/ft2 (718 Pa). (6.3.2)

Adhesion between the veneer units and the backing must have a shear strength of 50 psi (345 kPa) or
greater based on gross unit surface area when tested in accordance with ASTM C 482. Alternatively,
adhered units may be applied using the procedure found in MSJC Specification Article 3.3C. (6.3.2.4)

Chapter 7 – Glass Unit Masonry

Chapter 7 applies to glass unit masonry. The 2002 edition contains few changes from the 1999 version.
The provisions are largely based upon those in the three previous model building codes. Requirements are
primarily prescriptive and empirical.

Maximum wall areas are imposed by a design wind pressure graph for standard units, 3 7/8 in. (98.4 mm)
thick. When 3 in. (76.2 mm) thick units are used, a maximum wind pressure of 20 psf (958 Pa) is imposed
and the maximum wall area is reduced. The size of interior wall panels is limited to 250 ft2 (23.22 m2) and
150 ft2 (13.94 m2) for standard and thin units, respectively. (7.1, 7.2) Provisions regarding lateral support
for panels limited to one unit wide or one unit high are included. (7.3)
The MSJC Code also imposes requirements for expansion joints. (7.4)
Base surface treatment requires the surface on which glass unit masonry panels are placed to be coated
with an elastic waterproofing material. (7.5)

Glass unit masonry shall be built with Type S or N mortar. (7.6)

Glass unit masonry panels must contain a minimum amount of horizontal joint reinforcement. The MSJC
Code requires a minimum of two parallel W1.7 (MW11) wires spaced at 16 in. (406 mm) o.c. vertically.
Joint reinforcement is very important because the limitations on wall panel size are based upon the failure
of the reinforced section, rather than the first cracking strength of panels. (7.7)

THE MSJC SPECIFICATION (ACI 530.1/ASCE 6/TMS 602)

The MSJC Specification is a reference standard that an architect or engineer may cite in the contract
documents for any project. The MSJC Specification contains requirements for the contractor regarding
materials, construction and quality assurance. The MSJC Code requires compliance of construction of the
masonry with the MSJC Specification, so it is an integral part of the MSJC Code. The language is in
imperative voice for ease of interpretation and enforcement. The MSJC Specification should be referenced
in the contract documents and may be modified as required for the particular project.

The 2002 edition of the MSJC Specification consists of three components: a) Part 1 – General, b) Part 2 –
Products and c) Part 3 – Execution. The format was changed to the present one in 1995 to be more
consistent with the Construction Specifications Institute’s MASTERFORMAT.
Major changes in the 2002 edition relate to quality assurance and ease of use. Quality assurance is
established in conjunction with the MSJC Code and the MSJC Specification contains specific instructions
for the parties involved. The phrase “When required” was eliminated. Inclusion of this phrase in earlier
editions made it necessary for the user to extensively edit the MSJC Specification for application to a
particular project.

Requirements Checklists and Submittals

The requirements checklists help the designer to choose and specify the necessary products and
procedures found in the contract documents. Building codes set minimum requirements to protect property
and life safety. However, written contract documents may have more restrictive requirements than
provided in the building code. Adjustments for the particular project should be made by the designer by
reviewing the requirements checklists.

There are two checklists, mandatory and optional, that alert the designer to issues that must be addressed.
The mandatory list requires a choice on inspection, testing, material selection and items not provided on
the drawings or details of the project. The most significant change from the 1999 MSJC Specification in the
mandatory checklist is exclusion of determining specified compressive strength compliance. In addition,
the 1999 MSJC Specification required that the level of quality assurance be specified.

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Part 1 – General

In Part 1 it is stated that the MSJC Specification covers requirements for materials and construction of
masonry elements. The provisions govern any project unless other requirements are specifically stated in
the contract documents. (1.1)

Definitions are provided and are coordinated with those found in the MSJC Code. (1.2) All standards
referenced in the MSJC Specification are listed. These standards include material specifications, sampling
procedures, test methods, detailing requirements, construction procedures and classifications. The
references are updated to the most current edition at the time of the MSJC Code and Specification
approval. (1.3)

The compressive strength of each wythe of masonry must equal or exceed that specified by the engineer or
architect. The compressive strength must be verified by the contractor by one of two methods: unit
strength or prism test. The unit strength method is a means to evaluate the strength of masonry based
upon the tested compressive strength of individual units and the mortar type specified. The prism test
method requires the sampling and testing of masonry prisms built with the same types of materials that are
used in the masonry construction. The MSJC Specification specifies prism testing to be done in
accordance with ASTM C 1314, Standard Test Method for Compressive Strength of Masonry Prisms.
(1.4B) Adhesion of adhered veneer units to their backing is to be determined in accordance with ASTM C
482, Test Method for Bond Strength of Ceramic Tile to Portland Cement. (1.4C)

Part 1 provides a list of items to be included in project submittals. Submittals should include mortar and
grout mix designs and test results, masonry unit samples and certificates, samples of metal items such as
reinforcement and wall ties. This also includes construction procedures for cold- and hot-weather
construction. (1.5)

Quality assurance is required by the MSJC Specification. The duties and services of the testing agency,
inspection agency and contractor are specified and are dependent upon the level of quality assurance
required. Article 1.6A outlines the responsibilities of the testing agencies. Article 1.6B specifies the
responsibilities of the inspection agency. Article 1.6C contains the contractor’s services and duties. The
contractor must employ an independent testing laboratory to perform required tests, to document
submittals, certify product compliance, establish mortar and grout mix designs, provide supporting data for
changes requested by the contractor, or appeal rejection of material found to be defective. The contractor
must include in the submittals the results of all testing performed to qualify the materials and to establish
mix designs. Quality assurances are actions taken by the owner or the owner’s representative. They
provide assurance that actions of the contractor and supplier are in accordance with applicable standards
of good practice. Quality assurances are administrative policies and responsibilities related to quality
control measures that meet the owner’s quality objectives. Quality control is the action taken by the
producer or contractor. This is simply systematic performance of construction, testing and inspection to
verify that proper materials and methods are used.

Quality assurance involves inspection and testing, preparation and erection of the masonry structure.
Inspection is assumed for every masonry project under the MSJC Code, a change from previous masonry
standards. The level of inspection and the amount of testing depend upon the level of quality assurance
specified. The level of quality assurance is determined according to facility function, as defined by the
general building code, and the method of design. The MSJC Specification contains the same Quality
Assurance tables that are found in the MSJC Code. (1.6)

Sample panels for masonry walls are required for Level 2 or 3 quality assurance. The construction of a
grout demonstration panel, used to depart from the requirements of Articles 3.5 C-E is also a part of quality
assurance. (1.6D)

Requirements for delivery, storage and handling of masonry materials are stated in order to avoid
contamination that might reduce the quality of the constructed masonry. (1.7) Project-specific conditions
such as support of construction loads by the masonry and shoring and weather exposure during
construction must be addressed. Cold- and hot-weather construction requirements are included and are
mandatory when they apply. The provisions for cold-weather construction have been revised in the 2002
MSJC Specification. Provisions for both cold-and hot-weather construction are separated into preparation,
and construction protection. In most cases the methods to achieve the requirements are left to the
discretion of the contractor. (1.8)

Part 2 – Products

This section lists the available American Society for Testing and Materials (ASTM) standards for masonry
materials, including masonry units, mortar, grout, reinforcement and metal accessories. Specific
requirements are given if an appropriate ASTM standard does not exist. Referenced ASTM standards for
brick and tile are C 34, C 56, C 62, C 126, C 212, C 216, C 652, and C 1088. There are provisions for
spacing of cross wires in joint reinforcement that are not included in standard for this material. Minimum
corrosion protection requirements for metal items are stated including galvanized and epoxy coatings.
Requirements for corrosion protection of bonded and unbonded prestressing tendons are also included.
Criteria are specified for prestressing anchorages, couplers and end blocks. An accessories section
provides requirements on contraction joint material, expansion joint material, asphalt emulsions, masonry
cleaners and joint fillers. (2.1-2.5)

The MSJC Specification contains requirements for the mixing of mortar and grout. Time of mixing and
additives to mortar are limited. The grout must meet ASTM C 476 and be furnished and placed with a
slump between 8 in. (200 mm) and 11 in. (275 mm). (2.6)
Standard fabrication limits are stated for reinforcement and for prefabricated masonry panels. These
include bend and hook requirements for reinforcing bars. Prefabricated masonry panels must conform to
the provisions of ASTM C 901. (2.7)

Part 3 – Execution

The execution of the work includes initial inspection; preparation; masonry erection; reinforcement, tie and
anchor installation; grout placement; prestressing tendon installation and stressing procedure; field quality
control; and cleaning. Dimensional tolerances for foundations on which masonry is placed are provided
and should be measured prior to the start of masonry work. (3.1) As part of the preparation requirements,
clay or shale masonry units having initial absorption rates in excess of one gram per minute per in2
, as measured with ASTM C 67 must be pre-wetted, so the initial rate of absorption will not exceed one gram
per minute per in2 when the units are used. Cleanouts are required at the base of masonry to be grouted
whenever pour heights exceed 5 ft (1.5 m). (3.2)
Standard requirements for good workmanship are required by the MSJC Specification. These include the
requirement for completely filled mortar joints and grouted spaces. Proper support of masonry and bracing
during construction is required but is not prescribed. Dimensional tolerances for the masonry are listed to
ensure structural performance. The tolerances should not be used to establish appearance criteria, unless
specifically noted as such by the project specifications. (3.3)

Inspection of reinforcement and metal accessories is required to ensure that they have been properly
placed and are free of materials that hinder bond. Tolerances for locating and placing reinforcing steel, wall
ties, and veneer anchors are prescribed. Criteria for adjustable wall ties, which are repeated from the
MSJC Code, are included. Placement requirements for veneer anchors have been added (3.4)
Prior to grout placement, debris must be removed from grout spaces. The grouting requirements found in
the MSJC Code are repeated in the MSJC Specification. Maximum grout pour heights are determined by
the type of grout used and the dimensions of the grout space. Consolidation of grout is required to fill voids
created by the loss of water from grout by absorption into the masonry. Alternate grout placement
requirements, established through the use of a grout demonstration panel, are permitted. (3.5)
Prestressing tendon installation and stressing requirements include: tolerances; application and
measurement of the prestressing force; grouting bonded tendons; and burning and welding operations.
(3.6)

As part of field quality control, the specified compressive of masonry f’m is verified in accordance with
Article 1.6, Quality Assurance; grout is sampled and tested in accordance with Articles 1.4B and 1.6.
Provisions for cleaning exposed masonry surfaces complete the MSJC Specification. (3.8)

SUMMARY

This Technical Notes provides an overview to the criteria contained in the MSJC Code and Specification.
The discussion centers on the design requirements to be followed by architects and engineers and the
masonry specifications to be implemented by the contractor during construction. Changes to the Code and
Specification in the 2002 editions are emphasized. The MSJC Code and Specification provide the designer
with coordination between the design and construction phases of all masonry buildings.

The information and suggestions contained in this Technical Notes are based on the available data and the
experience of the engineering staff of the Brick Industry Association. The information contained herein
must be used in conjunction with good technical judgment and a basic understanding of the properties of
brick masonry. Final decisions on the use of the information contained in this Technical Notes are not
within the purview of the Brick Industry Association and must rest with the project architect, engineer and
owner.

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Brick Masonry Material Properties

Abstract: Brick masonry has a long history of reliable structural performance. Standards for the structural design
of masonry which are periodically updated such as the Building Code Requirements for Masonry Structures (ACI
530/ASCE 5/TMS 402) and the Specifications for Masonry Structures (ACI 530.1/ASCE 6/TMS 602) advance the
efficiency of masonry elements with rational design criteria. However, design of masonry structural members
begins with a thorough understanding of material properties. This Technical Notes is an aid for the design of brick
and structural clay tile masonry structural members. Clay and shale units, mortar, grout, steel reinforcement and
assemblage material properties are presented to simplify the design process.
Key Words: brick, grout, material properties, mortar, reinforcement, structural clay tile.
INTRODUCTION

The Masonry Standards Joint Committee (MSJC) has developed the Building Code Requirements for Masonry
Structures (ACI 530/ASCE 5/TMS 402) and the Specifications for Masonry Structures (ACI 530.1/ASCE 6/TMS
602). In this Technical Notes, these documents will be referred to as the MSJC Code and the MSJC
Specifications, respectively. Their contents are reviewed in Technical Notes 3. The MSJC Code and
Specifications are periodically revised by the MSJC and together provide design and construction requirements
for masonry. The MSJC Code and Specifications apply to structural masonry assemblages of clay, concrete or
stone units.

This Technical Notes is a design aid for the MSJC Code and Specifications. It contains information on clay and
shale units, mortar, grout, steel reinforcement and assemblage material properties. These are used in the initial
stages of a structural design or analysis to determine applied stresses and allowable stresses. Material properties
are explained to aid the designer in selection of materials and to provide a better understanding of the structural
properties of the masonry assemblage based on the materials selected.
CONSTITUENT MATERIAL PROPERTIES

Because brick masonry is bonded into an integral mass by mortar and grout, it is considered to be a
homogeneous construction. It is the behavior of the combination of materials that determines the performance of
the masonry as a structural element. However, the performance of a structural masonry element is dependent
upon the properties of the constituent materials and the interaction of the materials as an assemblage. Therefore,
it is important to first consider the properties of the constituent materials: clay and shale units, mortar, grout and
steel reinforcement. This will be followed by a discussion of the behavior of their combination as an assemblage.
Clay and Shale Masonry Units

There are many variables in the manufacturing of clay and shale masonry units. Primary raw materials include
surface clays, fire clays, shales or combinations of these. Units are formed by extrusion, molding or dry-pressing o o o o and are fired in a kiln at temperatures between 1800 F and 2100 (980 C and 1150 C). These variables in
manufacturing produce units with a wide range of colors, textures, sizes and physical properties. Clay and shale
masonry units are most frequently selected as a construction material for their aesthetics and long-term
performance. Consequently, material standards for clay and shale masonry units contain requirements to ensure
that units meet a level of durability and visual and dimensional consistency. Clay and shale masonry units used in
structural elements of building constructions are brick and structural clay tile. Material standards for brick and
structural clay tile include: ASTM C 216 (facing brick), ASTM C 62 (building brick), ASTM C 652 (hollow brick),
ASTM C 212 (structural clay facing tile) and ASTM C 34 (structural clay load-bearing tile).

While brick and structural clay tile are both visually appealing and durable, they are also well-suited for many
structural applications. This is primarily due to their variety of sizes and very high compressive strength. The
material properties of brick and structural clay tile which have the most significant effect upon structural
performance of the masonry are compressive strength and those properties affecting bond between the unit and
mortar, such as rate of water absorption and surface texture.
Unit Compressive Strength. The compressive strength of brick or structural clay tile is an important material
property for structural applications. In general, increasing the compressive strength of the unit will increase the
masonry assemblage compressive strength and elastic modulus. However, brick and structural clay tile are
frequently specified by material standard rather than by a particular minimum unit compressive strength. ASTM
material standards for brick and structural clay tile require minimum compressive strengths to ensure durability,
which may be as little as one-fifth the actual unit compressive strength. A recent Brick Institute of America survey
of United States brick manufacturers resulted in a data base of unit properties [6]. A subsequent survey of
structural clay tile manufacturers was conducted. The compressive strengths of brick and structural clay tile
evaluated in these surveys are presented in Table 1. As is apparent, all types of brick and structural clay tile
typically exhibit compressive strengths considerably greater than the ASTM minimum requirements. Compressive
strength of brick and structural clay tile is determined in accordance with ASTM C 67 Method of Sampling and
Testing Brick and Structural Clay Tile.

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1
Extruded only.
2
Made from other materials or a combination of materials.
3
Based on gross area.

Unit Texture and Absorption. Unit texture and absorption are properties which affect the bond strength of the
masonry assemblage. In general, mortar bonds better to roughened surfaces, such as wire cut surfaces, than to
smooth surfaces, such as die skin surfaces. Cores or frogs provide a means of mechanical interlock. The bond
strength of sanded surfaces is dependent upon the amount of sand on the surface, the sand’s adherence to the
unit and the absorption rate of the unit at the time of laying.
In practically all cases, mortar bonds best to a unit whose suction at the time of laying is less than 30 g/min/30 in2
(1.55 kg/min/m2). Generally, molded units will exhibit a higher initial rate of absorption than extruded or drypressed units. Unit absorption at the time of laying is an alterable property of brick and structural clay tile. In
accordance with the MSJC Specifications, units with initial rate of absorption in excess of 30 g/min/30 in.2 (1.55
kg/min/m2) should be wetted to reduce the rate of water absorption of the unit prior to laying. In addition, suction of
very absorptive units may be accommodated by using highly water-retentive mortars.
Mortar

The material properties of mortar which influence the structural performance of masonry are compressive
strength, bond strength and elasticity. Because the compressive strength of masonry mortar is less important than
bond strength, workability and water retentivity, the latter properties should be given principal consideration in
mortar selection. Mortar materials, properties and selection of masonry mortars are discussed in Technical Notes
8 Series. Mortar should be selected based on the design requirements and with due consideration of the MSJC
Code and Specifications provisions affected by the mortar selected.

Laboratory testing indicates that masonry constructed with portland cement-lime mortar exhibit greater flexural
bond strength than masonry constructed with masonry cement mortar or air-entrained portland cement-lime
mortar of the same Type. This behavior is reflected in the MSJC Code allowable flexural tensile stresses for
unreinforced masonry, which are based on the mortar Type and mortar materials selected. In addition, masonry
cement mortars may not be used in Seismic Zones 3 and 4.

Other MSJC Code and Specifications provisions are the same for portland cement-lime mortars, masonry cement
mortars and air-entrained portland cement-lime mortars of the same Type. These include the modulus of elasticity
of the masonry, allowable compressive stresses for empirical design and the unit strength method of verifying that
the specified compressive strength of masonry is supplied. Following is a general description of the structural
properties of each Type of mortar permitted by the MSJC Code and Specifications.

Type N Mortar. Type N mortar is specifically recommended for chimneys, parapet walls and exterior walls subject
to severe exposure. It is a medium bond and compressive strength mortar suitable for general use in exposed
masonry above grade. Type N mortar may not be used in Seismic Zones 3 and 4.

Type S Mortar. Type S mortar is recommended for use in reinforced masonry and unreinforced masonry where
maximum flexural strength is required. It has a high compressive strength and has a high tensile bond strength
with most brick units.

Type M Mortar. Type M mortar is specifically recommended for masonry below grade and in contact with earth,
such as foundation walls, retaining walls, sewers and manholes. It has high compressive strength and better
durability in these environments than Type N or S mortars.

For compliance with the MSJC Specifications, mortars should conform to the requirements of ASTM C 270
Specification for Mortar for Unit Masonry. Field sampling of mortar for quality control should follow the procedures
given in ASTM C 780 Test Method for Preconstruction and Construction Evaluation of Mortars for Plain and
Reinforced Unit Masonry. Test procedures for masonry mortars are covered in Technical Notes 39 Series.
Grout
Grout is used in brick masonry to fill cells of hollow units or spaces between wythes of solid unit masonry. Grout
increases the compressive, shear and flexural strength of the masonry element and bonds steel reinforcement
and masonry together. For compliance with the MSJC Specifications, grout which is used in brick or structural
clay tile masonry should conform to the requirements of ASTM C 476 Specification for Grout for Masonry. Grout
proportions of portland cement or blended cement, hydrated lime or lime putty, and coarse or fine aggregate are
given in Table 2

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compressive strength of the grout and the amount of grout shrinkage. Tests indicate that the total amount of water
absorbed from grout by hollow clay units appears to be more dependent on the initial water content of the grout
than the absorption properties of the unit [3]. Grouts with high initial water content exhibit more shrinkage than
grouts with low initial water contents. Consequently, use of a non-shrink grout admixture is recommended to
minimize the number of flaws and shrinkage cracks in the grout while still producing a grout slump of 8 to 11 in.
(200 to 280 mm), unless otherwise specified.
The MSJC Specifications require grout compressive strength to be at least equal to the specified compressive
strength of masonry, f’m, but not less than 2,000 psi (13.8 MPa) as determined by ASTM C 1019 Method of
Sampling and Testing Grout. Test procedures for grout are explained in more detail in Technical Notes 39 Series.
In general, the compressive strength of ASTM C 476 grout by proportions will be greater than 2,000 psi (13.8
MPa). Prediction of the compressive strength of grout which is proportioned in accordance with ASTM C 476 is
difficult because of the many possible combinations of materials, types of materials and construction conditions.
However, ASTM C 476 grout proportions produce a rich mix which is recommended to complement the high
compressive strength of brick and structural clay tile.
Steel Reinforcement
Steel reinforcement for masonry construction consists of bars and wires. Reinforcing bars are used in masonry
elements such as walls, columns, pilasters and beams. Wires are used in masonry bed joints to reinforce
individual masonry wythes or to tie multiple wythes together. Bars and wires have approximately the same
modulus of elasticity, which is stated in the MSJC Code as 29,000 ksi (200,000 MPa). In general, wires tend to
achieve greater ultimate strength and behave in a more brittle manner than reinforcing bars. Common bar and
wire sizes and their material properties are given in Table 3. As stated in the MSJC Specifications, steel
reinforcement for masonry structural members should comply with one of the material standards given in Table 4.

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ASSEMBLAGE MATERIAL PROPERTIES
The properties of the constituent materials discussed previously combine to produce the brick or structural clay
tile masonry assemblage properties. Following is a discussion of the material properties of the masonry
assemblage.
Compressive Strength
Perhaps the single most important material property in the structural design of masonry is the compressive
strength of the masonry assemblage. The specified compressive strength of the masonry assemblage, f’m, is used
to determine the allowable axial and flexural compressive stresses, shear stresses and anchor bolt loads given in
the MSJC Code.
The compressive strength of the masonry assemblage can be evaluated by the properties of each constituent
material, termed in the MSJC Specifications the “Unit Strength Method,” or by testing the properties of the entire
masonry assemblage, termed the “Prism Testing Method.” These methods are not to be used to establish design
values; rather, they are used by the contractor to verify that the masonry achieves the specified compressive
strength, f’m.
Unit Strength Method. A benefit of verifying compliance of the compressive strength of masonry by unit, mortar
and grout properties is the elimination of prism testing. Each of the materials in the masonry assemblage must
conform to ASTM material standards mentioned in previous sections of this Technical Notes. For compliance with
these material standards, the compressive strength of the unit and the proportions or properties of the mortar and
grout must be evaluated. Not surprisingly, there have been attempts by numerous researchers to accurately
correlate the assemblage compressive strength with unit, mortar and grout compressive strengths. Testing an
assemblage of three materials produces a large scatter of compressive strengths covering all possible
combinations of materials. Therefore, estimates of the masonry assemblage compressive strength based on unit,
mortar and grout properties are necessarily conservative. The correlations provided in the MSJC Specifications,
shown in Table 5, between unit compressive strength, mortar type and the masonry assemblage compressive
strength represent a lower-bound to experimental data. In addition, the MSJC Specifications unit strength method
does not directly address variable grout strength, multi-wythe construction or the influence of joint reinforcement
on the compressive strength of the masonry assemblage. Consequently, compliance with the specified
compressive strength of masonry by prism testing will always produce a more accurate and optimum use of brick
or structural clay tile masonry’s compressive strength than the unit strength method.
The conservative nature of Table 5 should not be overlooked by the designer. A comparison of the predicted
assemblage compressive strength by the unit strength method in the MSJC Specifications and a data base of
actual brick masonry prism test results [1] reveals this conservatism. The average compressive strength of prisms
of solid brick units was found to be about 1.7 times the masonry compressive strength predicted by Table 5. The
average compressive strength of prisms of hollow units ungrouted and grouted was found to be 1.9 and 1.4 times
the compressive strengths predicted by Table 5, respectively.

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Prism Test Method. Prism testing of brick or structural clay tile masonry provides a number of advantages over
constituent material testing alone. The primary benefit of prism testing is a more accurate estimation of the
compressive strength of the masonry assemblage. Another benefit of prism testing is that it provides a method of
measuring the quality of workmanship throughout the course of a project. Low prism strengths may indicate
mortar mixing error or poor quality grout.

The MSJC Specifications permit testing of masonry prisms to show conformance with the specified compressive
strength of masonry, f’m. In addition, the material components must meet the appropriate standards of quality.
Masonry prisms are tested in accordance with ASTM E 447 Test Methods for Compressive Strength of Masonry
Prisms, Method B as modified by the MSJC Specifications. At least three prisms are required by the MSJC
Specifications for each combination of materials. The average of the three tests must exceed f’m. Further
explanation of prism testing procedures is provided in Technical Notes 39B.

Shear Strength

The shear strength of a masonry assemblage may be separated into four parts: 1) the shear strength of the unit,
mortar and grout assemblage, 2) the effect of the shear span-to-depth ratio, M/Vd, 3) the enhancement of shear
strength due to compressive stress, and 4) the contribution of shear reinforcement in the masonry assemblage.
All four phenomenon are represented in the allowable shear stresses provided in the MSJC Code. However, only
the first and fourth items are controlled by material properties. Items two and three vary with member size and
applied loads.

The shear strength of the masonry assemblage is directly related to the properties of the unit, mortar and grout.
Shear failure of a unit-mortar assemblage is by splitting of units, step-cracking in mortar joints, or a combination of
the two. Unit splitting strength is increased by increasing the compressive strength of the unit. In general, unit
splitting is not a common shear failure mode of brick or structural clay tile masonry. Unit splitting occurs in
masonry assemblages of weak units and strong mortar and may also occur in shear walls which are heavily
axially loaded. Cracking in mortar joints is the more common shear failure mode for brick and structural clay tile
masonry assemblages. Mortar joint failure occurs by sliding along bed joints and separation of head joints. Mortar
joint shear failure is affected by bond strength and the frictional characteristics between the mortar and the unit. In
general, a unit-mortar combination which provides greater bond strength will also provide greater shear strength.
Grouting the masonry assemblage will also increase shear strength by providing a shear key between courses.
The shear strength of a masonry assemblage may be evaluated in accordance with ASTM E 519 Test Method for
Diagonal Tension (Shear) in Masonry Assemblages. The contribution of unit, mortar and grout to the allowable
shear stresses stated in the MSJC Code are based on ASTM E 519 tests of masonry assemblages.

Steel reinforcement may be added to the masonry assemblage to increase shear strength. Shear reinforcement
should be provided parallel to the direction of applied shear force. The MSJC Code also requires a minimum
amount of reinforcement perpendicular to the shear reinforcement of one-third the area of shear reinforcement.
When shear reinforcement is provided in accordance with the MSJC Code, allowable shear stresses given in the
MSJC Code for reinforced masonry are increased three times for flexural members and one and one-half times
for shear walls.

Flexural Tensile Strength

Reinforced brick and structural clay tile masonry is considered cracked under service loads and the flexural
tensile strength of the masonry is neglected in design. However, cracking of an unreinforced brick or structural
clay tile masonry member constitutes failure and must be avoided. Thus, flexural tensile strength is an important
design consideration for unreinforced masonry. Flexural tensile strength is the bond strength of masonry in
flexure. It is a function of the type of unit, type of mortar, mortar materials, percentage of grouting of hollow units
and the direction of loading. Workmanship is also very important for flexural tensile strength, as unfilled mortar
joints or dislodged units have no mortar-to-unit bond strength.

Allowable flexural tensile stresses stipulated in the MSJC Code for unreinforced masonry are given in Table 6.
The allowable flexural tensile stresses for portland cement-lime mortars are based on full-size wall tests in
accordance with ASTM E 72 Method of Conducting Strength Tests of Panels for Building Construction. Values for
masonry cement and air-entrained portland cement-lime mortars are based on reductions obtained with
comparative testing. Flexural tensile strength may be evaluated by testing small-scale prisms in accordance with
ASTM E 518 Test Method for Flexural Bond Strength of Masonry or ASTM C 1072 Test Method for Measurement
of Masonry Flexural Bond Strength, but these results may not directly correlate to the allowable flexural tensile
stresses in the MSJC Code

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1*For partially grouted masonry allowable stresses shall be determined on the basis of linear interpolation between hollow units which are fully grouted or ungrouted and hollow units based on amount of grouting.

Elastic Modulus

The elastic modulus of the masonry assemblage, in combination with the moment of inertia of the section,
determines the stiffness of a brick or structural clay tile masonry structural element. Elastic modulus is the ratio of
applied load (stress) to corresponding deformation (strain). The elastic modulus is roughly proportional to the
compressive strength of the masonry assemblage. Testing of brick masonry prisms indicates that the elastic
modulus of brick masonry falls between 700 and 1200 times the masonry prism compressive strength [4]. If the
Unit Strength Method is used to show compliance with the specified compressive strength of masonry, f’m, an
accurate estimation of the actual compressive strength of the masonry assemblage may not be known.
Consequently, the elastic modulus of the masonry assemblage is determined by the mortar type and the unit
compressive strength. See Table 7. The data in Table 1 can be used to estimate the modulus of elasticity of the
masonry assemblage for the type of unit selected.

The elastic modulus of grout is computed as 500 times the compressive strength of the grout in accordance with
the MSJC Code. In general, the elastic modulus of grout and the elastic moduli of brick or structural clay tile and
mortar masonry assemblages are comparable and are often considered equal for design calculations. However,
the MSJC Code recommends that the method of transformation of areas based on relative elastic moduli be used
for computation of stresses in grouted masonry elements.

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Dimensional Stability

Dimensional stability is also an important property of the masonry assemblage. Expansion and contraction of the
brick or structural clay tile masonry may exert restraining stresses on the masonry and surrounding elements.
Material properties which affect dimensional stability of clay and shale unit masonry are moisture expansion,
creep and thermal movements. Effects of these phenomenon may be evaluated by the coefficients provided in the
MSJC Code, which are listed in Table 8. The coefficients in Table 8 represent average quantities for moisture
expansion and thermal movements and an upper-bound value for creep. Moisture expansion and thermal
expansion and contraction are independent and may be added directly. The magnitude of creep of clay or shale
unit masonry will depend upon the amount of load applied to the masonry element.

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SUMMARY

This Technical Notes contains information about the material properties of brick and structural clay tile masonry.
This information may be used in conjunction with the MSJC Code and Specifications to design and analyze
structural masonry elements. Typical material properties of clay and shale masonry units, mortar, grout,
reinforcing steel and combinations of these are presented.

The information and suggestions contained in this Technical Notes are based on the available data and the
experience of the engineering staff of the Brick Institute of America. The information contained herein must be
used in conjunction with good technical judgment and a basic understanding of the properties of brick masonry.
Final decisions on the use of the information contained in this Technical Notes are not within the purview of the
Brick Institute of America and must rest with the project architect, engineer and owner.

REFERENCES

1. Atkinson, R.H., “Evaluation of Strength and Modulus Tables for Grouted and Ungrouted Hollow Unit
Masonry,” Atkinson-Noland and Associates, Inc., Boulder, CO, November 1990, 47 pp.
2. Building Code Requirements for Masonry Structures and Commentary (ACI 530/ASCE 5/TMS 402-92)
and Specifications for Masonry Structures and Commentary (ACI 530.1/ASCE 6/TMS 602-92), American
Concrete Institute, Detroit, MI, 1992.
3. Kingsley, G.R., et al., “The Influence of Water Content and Unit Absorption Properties on Grout
Compressive Strength and Bond Strength in Hollow Clay Unit Masonry,” Proceedings 3rd North American
Masonry Conference, The Masonry Society, Boulder, CO, June 1985, pp. 7:1-12.
4. Plummer, H.C., Brick and Tile Engineering, Brick Institute of America, Reston, VA, 1977, 466 pp.
5. “Steel Reinforcement Properties and Availability,” Report of ACI Committee 439, Journal of the
American Concrete Institute, Vol. 74, Detroit, MI, 1977, p. 481.
6. Subasic, C.A., Borchelt, J.G., “Clay and Shale Brick Material Properties – A Statistical Report,”
submitted for inclusion, Proceedings 6th North American Masonry Conference, The Masonry Society,
Boulder, CO, June 1993, 12 pp.