Potential Effects of Contaminants on Modified Bitumen Sheet Materials

Roof membrane systems are intended to provide protection from natural elements, such as rain, snow,
hail, and sleet. Systems that are properly designed, installed, and maintained should provide the user
with long-term satisfactory protection from these elements. Some roof membrane systems, such as
those installed on certain factories, restaurants, and other buildings with a high probability for unusual
levels of contamination, require special care in design. The presence of greases, oils, bacteria, and/or
other agents on the roof surface that may adversely affect the integrity of the roof membrane should be
taken into consideration. The specifier should select the type of roof membrane system that will best
satisfy the performance requirements based upon the number, type, and expected quantity of
contaminants present. This document is intended to aid the specifier by highlighting the effects that
various contaminants, if not considered in the design phase, may have on polymer modified bitumen
Effects of Oils and Greases
Modified bitumen roof membranes may be adversely affected by exposure to cooking oils (animal or
vegetable) and greases. Unprotected membrane may experience degradation around exhaust vents,
where the roof membrane has repeated contact with these contaminants. The organic substances
contained within oils and greases may weaken and eventually break down the polymer-bitumen
network, causing premature failure of the roof.
Petroleum-derived products, such as greases that leak from rooftop equipment, or hydrocarbons such
as gasoline, paint thinners and kerosene spilled during maintenance operations, may likewise cause
degradation of the roof. Due to the relatively fast evaporation rate of many hydrocarbon materials, any
detrimental effects caused by a one-time contamination may be shorter term and less severe in nature
than those caused by greases or recurring spills. Always report such contamination incidents to the
membrane manufacturer for guidance.
Effects of Bacteria and Fungi
Factories producing foods such as potato pulp and dry milk have reported cases of modified bitumen
membrane deterioration due to bacteria and/or other causes. These conditions may result in “mud
cracking,” which may ultimately lead to damage of the modified bitumen membrane. Excessive bird
droppings may also cause degradation of the roof membrane due to a combination of solids build-up
and subsequent “mud cracking,” bacteria, and the acidity of the droppings. The degree of degradation is
dependent upon the type of microorganism, temperature and other conditions. While certain roof
coatings can alleviate the effects of surface contaminants, the type and quality best suited for the
specific rooftop conditions, should be addressed with the membrane manufacturer.
Fungus growth, which typically occurs in hot, humid regions, does not cause the same detrimental
effects as “mud cracking” and bacterial attack and usually poses only aesthetic concerns.
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Effects of Other Chemicals
Other chemicals, such as solvents, acids, bases and oxidizing agents, may cause varying degrees of harm
to polymer-modified bitumen roof membranes, such as swelling, softening (reducing resistance to foot
traffic), and slumping of the bitumen compound of the membrane. Many modified bitumen sheet
materials may be applied using solvent-based cold process adhesives, and care should be taken to
ensure that the adhesive is approved for use by the membrane manufacturer and that the application
guidelines for adhesive quantity and flash-off (curing) are followed. Contact the roof membrane
manufacturer to obtain additional information regarding the effects of adhesives, chemicals, and
contaminants on modified bitumen sheet materials.
 Wherever possible, reduce or eliminate exposure of roofing components to contaminants.
 Determine the types and concentrations of contaminants that may be present on the roof. When
re-roofing, investigate what effects, if any, contaminants have had on the existing roof before
specifying and applying a new roofing system.
 Use commercially available traps and/or filters designed to capture contaminants exhausted from
rooftop equipment.
 Establish a roof maintenance program to monitor affected roof sections and to properly maintain
traps or filters.
 Provide positive drainage (at least 1/4” per foot roof slope) to prevent ponding in the affected
 If contaminant effects are minor, increase the number of plies and/or add resistant coatings to
provide adequate protection.
 Consider the use of properly specified roof coatings on roof areas where the roof membrane will
be exposed to contaminants.
 Investigate alternate venting designs that minimize or eliminate contamination of the roofing

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