Pressurized Canister Adhesives
When it comes to adhering roofing insulation, two-component polyurethane adhesives hold the largest market share in the commercial roofing market. While mechanically attaching insulation to steel decks is common, adhesives are frequently used to attach insulation to other decks and to add a second and even third layer of insulation with staggered joints (Figure 1), to reduce air migration and break the thermal bridging.
Historically, extrusion has been the most common method of applying a two-component insulation adhesive. For these applications, contractors typically use a large low-pressure dispensing cart, or an oversized caulk-gun-type of applicator.
The adhesive is typically dispensed in liquid beads that spread to several inches while rising ¾- to 1-inch above the substrate (Figure 2). Depending on the adhesive formulation, a chemical cure takes place quickly. Since the insulation is a component of the roofing assembly, contractors should follow membrane manufacturer recommendations for adhesive spacing.
In either case—carts or cartridges—the Part 1 and Part 2 components are mixed at the point when they are dispensed, allowing the chemical reaction to take place. Because the adhesive is not atomized, personal protection equipment (PPE) is typically limited to eye protection and gloves.
An alternative to box or drum containers and 1,500-ml cartridges, low-pressure canister adhesives have become the roofing adhesive of choice for many professionals. Pressurized canisters are differentiated from their non-pressurized counterparts in that these systems are self-contained and do not require any additional or external equipment or power (Figure 3).
Canisters are ideal for use on small to mid-size roofs and roofs with lots of penetrations and obstacles, where large dispensing equipment and carts can be difficult to manage.
Canisters also appeal to contractors who want better rooftop productivity when compared to adhesives supplied in 1,500-ml cartridges. Consider that adhesives applied from cartridges in a serpentine pattern have a yield of about 1.5 squares/cartridge. With canisters, the yield with the same fastening pattern is up to 35 squares/set. Depending on the size of the roof, the labor savings and increased application speed with canisters can be highly significant.
One of the biggest differences between adhesives packaged for use with other dispensing equipment and packaged in pressurized canisters, is that all external dispensing equipment requires some maintenance. Pressurized canister adhesives, by contrast, do not typically require any maintenance, so the time and labor associated with maintaining equipment is out of the equation.
Components, Accessories and Required Assembly
Canister sets are typically self-contained and include two tanks: Part 1 and Part 2. The components are mixed in the dispensing tip for a controlled chemical reaction during application. The adhesive is dispensed at low pressure and not atomized so typical PPE is limited to gloves and eye protection. These systems usually include a disposable hose secured to a hand applicator. Other components of the system include short mix tips, and longer extension tubes that enable roofers to stand upright during application for better ergonomics and less fatigue.
Canister-based adhesives are highly flexible and compatible with most commercial roof decks and substrates, including structural concrete, gypsum, cementitious wood fiber, lightweight insulating concrete, steel, plywood, smooth-surfaced built-up roofing systems, smooth and granular-surfaced modified bitumen, base sheets, some vapor barriers, and most insulation types, including expanded polystyrene, polyisocyanurate, high-density wood fiber, perlite, certain extruded polystyrene, and most cover boards.
Common application is to apply a continuous serpentine bead (Figure 4 - 5) at the prescribed spacing – typically 12 inches on center. Coverage rates vary depending on the manufacturer, but in general at 12 inches on center, installers should expect to yield anywhere from 20 to 35 squares of coverage per set.
(Figures 4 & 5)
One of the biggest differences between pressurized canisters and extruded applications, is the contractor’s ability to control the adhesive flow through the gun assembly. With carts and cartridge sets, adhesives will continue to flow from the mix tip for a short time after letting go of the trigger, making a clean stop difficult at best. While this may not seem like a huge benefit, it enables installers (with manufacturer approval) to apply parallel lines rather than a serpentine pattern. The ‘parallel-line’ method (Figure 6), can yield up to 42 squares of coverage per set, or approximately 20% more coverage per set when compared to the serpentine application method.
In addition, pressurized canisters also allow for easy ‘spattering’ on fleece membranes for great looking applications. Spattering refers to a process in which the adhesive is splattered onto the substrate in a random pattern of various size droplets vs. extruded in a serpentine or straight-line pattern (Figure 7). It can be difficult to gauge coverage rates accurately when spattering, but typical application rates range from 16 to 24 squares per canister set.
With pressurized canister adhesives, most manufacturers recommend that the adhesive be allowed to react before laying out the insulation. When dispensed, adhesives from canisters are ‘frothed’ but it takes a minute or two for the two parts to chemically react. Installers should work with the system manufacturer to clearly understand when the adhesive is ready for the board to be installed.
It is critical to work within the temperature guidelines provided whenever using pressurized canister adhesives. While bag-in-box and cartridge adhesives are also susceptible to temperature restrictions, non-pressurized dispensing systems are less sensitive when it comes to ambient temperature. With pressurized canisters, a drop in ambient temperature by just 6 to 10 degrees can reduce tank pressure and increase chemical viscosity within the canisters. Using canister adhesives below the suggested ambient temperatures (typically 40°F and rising) can potentially cause the product to be applied off-ratio or insufficiently mixed. It is also important that canisters be stored and dispensed at or around room temperature (i.e., 70° to 90°F). This ensures that there’s adequate pressure in the tanks and that the viscosity of each part is maintained to keep the final mixture “on-ratio”.
Two-part polyurethane adhesives in pressurized canisters have gained strong acceptance throughout North America in just a few years, appealing to a wide spectrum of the market for their ease-of-application, freedom from external dispensing equipment, and the potential of increased productivity per set and the related issue of qualified labor. Depending on the project and contractor’s approach, pressurized canisters can be an ideal solution. Learn more about the variety of OlyBond500 application options for more information.