Roofing and Insulation Adhesives Explained
Roof Online Staff
Table of Contents
– click to jump to section –
- Pictures of Roofing Adhesives
- Construction Definition – Adhesive
- How Adhesives Are Used in Roofing
- Roofing Adhesive Formulations Change Often
- Roofing Adhesive Application Temperatures
- Useful Links for Roofing Adhesive Information
Pictures of Roofing Adhesives
Construction Definition – Adhesive
A substance used to chemically bond two surfaces together. Contrast with fasteners, which attach building components mechanically.
How Adhesives Are Used in Roofing
Adhesives play several critical roles in roofing. In particular, adhesives are vital in single-ply low-slope (“flat”) roof systems which use EPDM, PVC, or TPO membranes, and often hold the entire system together.
Adhesives Instead of Roofing Fasteners
In flat roof systems where structural concrete decks make using mechanical fasteners (screws) impossible or impractical, adhesives are used to attach the bottom layer of insulation (and thus the entire system) to the roof deck.
Even with other deck types such as ribbed steel, where fasteners can be used, it’s fairly common for the base layer of insulation to be fastened to the deck while adhesives are used to attach everything else.
Adhesives can be used to bond multiple layers of insulation board to each other, adhesives can be used to bond a cover board layer to the insulation, and adhesives can be used to attach the waterproof roof membrane to the cover board.
Adhesives in Fully-Adhered Single-Ply Membrane Systems
When adhesives are used to attach an entire single-ply roof membrane, the roof system is known as a “fully-adhered system”.
“Fully-adhered” only refers to the attachment of the membrane itself, and the phrase is used to distinguish this attachment technique from mechanically-attached (screws) and ballasted (weighted down with stones or pavers) single-ply membrane systems.
A fully-adhered system may still use fasteners instead of adhesives to hold the cover board and insulation layers together as well as to the deck.
A very common insulation adhesive is two-part polyurethane foam, applied using special pressurized applicators.
Although fleece-back roof membranes are often installed in polyurethane foam, most membrane adhesives are one part, non-foaming products which are usually applied with rollers.
Adhesives in Built-Up Roofing
Specially-formulated roofing adhesives are almost never used in built-up roofing.
The hot asphalt or coal tar pitch that makes up the roofing membrane also functions as an adhesive, bonding the membrane to the cover board during installation, and can even be used to attach the system to the roof deck.
Bitumen-based cold-applied adhesives may be used sometimes when repairing these roofs.
Adhesives in Modified Bitumen Roof Systems
Modified bitumen systems, which are often installed using hot asphalt to bind the layers together, may instead use “cold-applied adhesives”.
These products are typically asphalt-based, and can be delivered to the roof from the factory in buckets and applied at the ambient temperature, so there’s no need to melt asphalt in a kettle and then pipe it to the roof.
They are poured out and spread with squeegees, and the roof components are set into them like they would be with hot asphalt.
Normal cold-applied adhesive formulations are known for having a very strong odor, which continues for days after the application while the adhesive cures. Great care needs to be taken to seal penetrations through the roof deck to prevent the odor from getting into the building.
Some newer formulations are designed to be “low-odor” and don’t release the volatiles that cause these odors.
Adhesives in Steep-Sloped Roofing
Steep-slope roofing (shingle, tile, slate, and some metal panel roofing) will almost never use adhesives as the primary attachment method for the roof covering, with the exception of the relatively new use of polyurethane foam adhesive to replace mortar as a method of attachment for clay and concrete tile roofs.
This is not to say that adhesives play no role in steep-slope roofing. Roofing adhesive, applied with a caulk gun or trowel, is an important component of asphalt shingle roofs.
While not used to attach the shingles to the roof deck, roofing adhesive is used to prevent wind-uplift of the shingles. This can be done by applying dabs of the adhesive (roof cement) under the ends of the shingle tabs of every shingle on the roof.
Many roofing contractors will not do this, as it’s time-consuming (and therefore expensive) and many homeowners do not think to ask them to do it. But by preventing wind damage, this technique can greatly increase the life expectancy of the roof.
Some professional roof consultants will even specify two spots of roof cement under every single shingle tab on the roof, because it is so effective at preventing long-term damage.
Roof cement should also be heavily applied under the tabs of the rake edge shingles (along the sloped edges of the roof) because these areas are usually subjected to the strongest wind-uplift forces of any location on the roof.
In addition, minor roof repairs or emergency repairs on all types of shingle roofs are often made using roof adhesives, when proper repairs are considered too expensive or can’t be done immediately.
Roofing Adhesive Formulations Change Often
Roofing adhesive products, as with roof coatings and sealants, are subject to fairly frequent reformulations and chemical industry advances. It’s important to realize that this can affect what weather conditions, especially temperature, that the adhesives can be successfully used in.
Roofing Adhesive Application Temperatures
Reading product literature and strictly following manufacturer recommended guidelines is critical when using roofing adhesives. Many other roofing products give you a lot of leeway during installation, but adhesives don’t.
If you do not apply roofing adhesive within the recommended temperature range, you run the risk that the adhesive will not be able to bond properly with the substrate before it sets and becomes inert (usually within minutes).
Adhesive application temperature ranges are typically between 35 and 95 degrees Fahrenheit.
Manufacturers have recently started making more cold-tolerant products which can be applied in temperatures as low as 30 degrees.
A long-time rule of thumb in the industry, however, is that you never apply roofing adhesives when the temperature is below 40 degrees. If you can stick to that (stick to that!) policy, you should.
Useful Links for Roofing Adhesive Information
1. General: “MIL-HDBK-691B Department of Defense – Military Standardization Handbook – Adhesive Bonding” is a tremendously valuable resource for adhesive information. It has over 400 pages and was the US Department of Defense’s standard information source for adhesives until 2013. Although no longer an active source for the DoD, it contains fundamental information that will remain valid, although for the very latest in adhesive technology, you’ll have to look elsewhere.
3. Insulation Adhesive: “JM Two-Part Urethane Insulation Adhesive“. See this product data sheet at the Johns Manville website for information about a typical insulation adhesive used on low-slope roofs. This is only an example and other products and brands may be different.
4. Modified Bitumen: “Cold Adhesive SBS-Modified Bitumen Roofing Applications” is a basic overview put together by the Asphalt Roofing Manufacturers Association.
5. Tile Roofs: See Dupont’s TILE BOND™ Roof Adhesive YouTube video to get an idea of how polyurethane foam adhesive is used in the securement of tile roofs.
6. Manufacturers: See here for a list of roofing adhesive manufacturers.