Roof Coatings Manufacturers Association
The use of cold-applied modified bitumen (MB) membrane roofing systems is perhaps the fastest growing segment of the cold-applied roofing industry. Cold-applied adhesives were initially used as the inter-ply adhesive in the construction of built-up roofing
systems. The use of cold-applied adhesives has expanded more recently, and they are now an excellent method for adhering modified bitumen roofing systems as well. For obvious reasons, the use of cold-applied adhesives in roofing provides an attractive alternative to the use of hot asphalt or open-flames. This article will focus on the application of cold-applied adhesives for MB
membranes.
The term “cold-applied” is used to describe a type of product that can be applied at ambient temperature. The base resin for these adhesives generally consists of bitumen (asphalt or coal tar). Additional components may include: a polymer modifier, petroleum based solvents, fibers and fillers. The polymer chosen to modify the asphalt depends on the final properties desired. The most common modifiers for modified bitumen cold-applied adhesives are:
■■ Styrene-Butadiene-Styrene (SBS),
■■ Styrene-Isoprene-Styrene (SIS),
■■ Styrene-Butadiene Rubber (SBR), and
■■ Styrene-Ethylene-Butylene-Styrene copolymers (SEBS).
Acrylics, butyl, neoprene and urethanes are also used as modifiers.
Like all roofing products, application is an important key to long-term, successful performance. The following are a number of items to consider when using cold-adhesive with modified bitumen membranes.
The rate of application is of primary importance when using any cold-applied adhesive. The adhesive must be applied at the manufacturer’s recommended rate and application temperature range, as excess material can trap solvent in the membrane, causing
membrane softening, slippage, or loss of granules. An excessive amount of adhesive can cause the membrane to float and retard full adhesion to the underlying substrate. Inadequate amounts of adhesive can result in an incomplete or weakened bond. Unless the laps are to be torched or heat welded, a visible bleeding-out or “bead” of adhesive should be seen at the laps during application in
accordance with the membrane m a n u f a c t u r e r ’s instructions. This is a visual way to ensure that the critical lap areas have received sufficient amounts of adhesive.
Cold-applied adhesives can be applied using a notched trowel, notched squeegee, roller, spray or automatic spreading equipment. Always follow the manufacturer’s directions for coverage rate and application method. Verify the correct coverage rate of the cold-applied adhesive by measuring the volume applied in a small pre-measured portion of the roof, by using a wet film gauge, or by using applicators with metered flow rates. Follow the membrane manufacturer’s recommendations for unrolling and relaxing modified
bitumen sheets prior to installation in cold-applied adhesive. A few application tips include: start with an approved clean, dry, smooth substrate; positive drainage is required; ensure that solvent vapors will not be drawn into the building; start at the lowest part of the
roof; install the adhesive evenly and at the recommended rate; and ensure the side and end laps are completely sealed. Cold-applied adhesives should not be used with membranes which have poly burn-off films.
Laps are critical and it is important to follow the membrane manufacturer’s guidelines for lap adhesion. Some manufacturers recommend that the laps be left dry until the field of the roof is complete, and then adhered separately with a heavier-bodied adhesive. The membrane manufacturer may specify that laps be rolled after application. Some materials are designed to have the laps heat (hot air or torch) welded. It is very important to keep foot traffic and equipment off finished portions of the roof until the adhesive has set, as weight can displace wet adhesive, creating a void and/or staining of the roofing granules.
Cold-applied adhesives typically take longer to set than a hot asphalt application. On slopes above ½ inch in 12 inches, membrane manufacturers often require rolls to be installed parallel to the slope (strapping), and nailed at the high point of the roll under the endlap (backnailing) to prevent slipping. Consult the membrane manufacturer for specific fastening requirements. It is good roofing practice in strapped roof application to have the lap facing away from the prevailing winds.
Consult membrane manufacturer’s installation instructions for acceptable application temperature ranges for membrane materials. Cold-applied adhesives can typically be installed at temperatures between 50˚F and 100˚ F (10˚ C to 38˚ C). Recommended product
temperature is between 70˚ F and 100˚ F (21˚ C to 38˚C). This will ensure that the adhesive is the proper viscosity for application.
Full set times are dependent on many factors, including temperature, humidity, solvent and coverage rates. Generally, colder temperatures, high humidity or high application rates retard set up time of the adhesive. For the specific application temperatures and rates, storage conditions and mixing instructions, consult with the individual manufacturer’s recommendations.
One factor that must be kept in mind when using a cold-applied adhesive is that solvent vapor is released as the material dries. Care must be taken to ensure that solvent vapors do not get into the ventilation system. Some adhesives may be manufactured with solvents that are combustible; care should be taken that vapors do not come in contact with sources of ignition.
Cold-applied adhesives provide another successful installation method for modified bitumen membranes.
For additional information about roof coatings, adhesives and cements, visit www.RoofCoatings.org. The Washington, D.C.-based Roof Coatings Manufacturers Association is the national trade association representing the manufacturers of asphaltic and solar reflective roof coatings, and the suppliers of materials, equipment and services to the industry. RCMA has more than 70 members who manufacture or supply roof coatings products. It maintains industry expertise in building codes and standards, technical research and end-user education.
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