Tackling a Sticky Subject: Adhesives

While it may be true that a rose is a rose is a rose, not all roofing adhesives are alike. There are insulation adhesives and there are membrane bonding adhesives. These can take the form of solvent-based adhesives, water-borne adhesives, solids-based adhesives, or tape adhesives.

As fully adhered installations of flexible roof membranes become more popular, contractors need to understand the differences in adhesive types in order to optimize their results. To help them learn more about the wide range of available options, SPRI's Adhesives & Tapes subcommittee is preparing several documents on adhesive use for inclusion in the next edition of SPRI's comprehensive manual, "Flexible Membrane Roofing: A Professional's Guide to Specifications."

Last year's SPRI statistics showed that fully adhered projects represented 34% of all thermoset projects nationwide, as well as 11% of all thermoplastic installations. Year-to-date SPRI statistics for 1999 indicate that adhered systems continue to gain market share in a number of areas.

In light of this increased adhesives usage, SPRI's upcoming selection and application guides are especially timely. Insulation adhesives tend to differ from membrane bonding adhesives, explains one expert, in that they tend to be thicker and a little heavier in body. These attributes facilitate their use on rougher or more uneven surfaces.

Membrane bonding adhesives are typically used over more even surfaces, so they tend to be lighter bodied.

Plus, they need to be properly formulated in order to bond to specific membranes. Using the wrong adhesive could degrade a membrane over time, even if it does produce a good bond. Always follow manufacturer recommendations for best results.

Insulation Adhesives

In general, contractors can choose from six different generic types of adhesives for attaching insulation boards. (However, not every adhesive can be used on every type of insulation. ) These are:

Solvent-Based Asphalt Adhesives;

Solvent-Based Non-Asphalt Adhesives;

Water-Borne Asphalt Emulsion Adhesives;

Water-Borne Non-Asphalt Adhesives;

Polyurethane-Based Adhesives;

Hot Asphalt.

Membrane Bonding Adhesives

A total of eight different membrane bonding adhesives are available in all (though, again, contractors should follow manufacturer guidelines when choosing what to use).

Solvent-Based Contact Adhesives (used on thermoset and thermoplastic membranes);

Solvent-Based Single-Side Adhesives (for thermoset and thermoplastic membranes);

Solvent-Based Asphaltic Adhesives (for modified bitumen membranes);

Water-Borne Contact Adhesives (thermoset and thermoplastic membranes);

Water-Borne Single-Side Adhesives (thermoset and thermoplastic membranes);

Water-Borne Asphaltic Emulsion Adhesives (for modified bitumens);

Polyurethane-Based Adhesives (for fleece-backed thermoset and thermoplastic membranes);

Hot Asphalt (for fleece-backed thermoset and thermoplastic membranes, as well as modified bitumens).

Seam Tapes

Seam tapes have wrapped up a large market share in the last decade. From less than 10% of the market in 1989, according to industry sources, tapes now control about 70% of the U.S. market.

Handling Tips

Environmental limitations can also limit the use of some adhesives. High humidity, coastal environments or cold weather that can lead to product freezing can be obstacles for water-borne adhesives. Conversely, moisture-cured urethanes can be limited by low-humidity, desert-type environments. Common handling and safety advice typically recommends storing adhesives in warm, indoor environments during periods of cooler outside temperatures. Ventilate when used in enclosed areas.

This article previously appeared in the November 1999 issue of RSI Magazine.

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