Avoiding Common Mistakes with Two-Component Low-Rise Adhesives

Two-component low-rise urethane adhesives have become increasingly popular since their introduction to the single-ply roofing industry over 30 years ago. Since 2015, the two-component low-rise urethane adhesive market has significantly expanded with the introduction of new low-pressure dispensing equipment.

While low-rise urethane adhesives provide several advantages when designing a roof to withstand extreme weather events, there are common mistakes that can affect the application of the product.

Below are common mistakes that can occur during two-component urethane adhesive applications:

1. Gaps between the deck and wall/penetration that are not sealed: Unsealed gaps allow humid air to enter the roofing assembly and condensate on the deck, weakening the insulation facer. A physical air block using foam or a backer rod in addition to VapAir Seal 725TR or Pressure-Sensitive Flashing is required.

2. Loose material or moisture on the deck: Dirt, dust, debris, and loose felts will compromise the adhesive bond. After brooming, use a blower to remove any residual contamination. Deck must be dry.

3. Un-weathered asphalt wasn’t primed: Versico requires the use of CAV-GRIP® 3V or 702 Primer over weathered asphalt when beads are spaced at 4”, 6", or 12" o.c.. Adhesion to un-weathered asphalt is doubled with CAV-GRIP 3V or 702 Primer, with CAV-GRIP 3V being the preferred method. Fastening the first layer of insulation is an option.

4. Depressions in the deck not accounted for: Hard insulation boards will bridge depressions or deflections in the deck. These areas should be marked ahead of time so that more adhesive or thicker adhesive can be applied to compensate.

5. Pencil-thin beads applied: Proper application and performance requires a minimum ½"-wide wet bead of adhesive that will foam out to around 1” to 1½”.

6. Bead spacing exceeds specification: Bead spacing has a direct impact on the uplift performance of the assembly. If the spec calls for 6" o.c. and adhesive is applied at 8" or 9" o.c., the ultimate uplift strength will be reduced. A 4" o.c. spacing requires 12 beads per 4' x 4' board. A 6" o.c. spacing requires 8 beads per 4' x 4' board. A 12" o.c. spacing requires 4 beads per 4' x 4' board. (Maximum 4' x 4' insulation boards when adhesive is extruded at 12" o.c. or when boards exceed 4" thickness, or 4' x 8' insulation boards when adhesive is applied in full spray, 4", or 6" beads.)

7. 12" bead spacing used in corners and perimeters: Corners and perimeters experience more wind uplift pressure, which is why Versico requires tighter bead spacing in these areas. 12" bead spacing is not acceptable in corners or perimeters. Know the spacing requirements prior to starting the job.

8. Thin application over gravel BUR: A thicker application of adhesive is required over a properly prepared gravel BUR. The foam must rise 3/8" above the remaining gravel, or it won’t touch the board.

9. Not waiting for “string/gel” time: If insulation boards are set prior to the adhesive reaching string- or gel-like consistency, the foam cells collapse back to a liquid and the adhesive loses a significant amount of its holding power. This is very important to note.

10. No weighted roller used, and no relief cuts or constant weight applied: Rigid insulation boards must be forced into the adhesive with a 150-lb. segmented weighted roller. Relief cuts and constant weight are sometimes required to promote a solid bond. Rolling the boards at the 5-minute mark allows adhesive to gain strength.

11. Not changing static mixing tips: When the Part-A side and Part-B side of 2-component urethane adhesives are mixed together, it creates a thermal reaction that produces the adhesive. The adhesive in small static mixing tips will begin to solidify after 15-20 seconds, meaning the tips must be changed to avoid off-ratio or clogged guns.

12. Not shaking Dual Tanks: Dual Tanks use a propellant to disperse the adhesive. To activate the propellant, the tanks must be shaken for 30 seconds prior to using. When the tanks are not agitated, the adhesive will not disperse properly, reducing coverage rates or producing off-ratio adhesive.

13. Cold or hot adhesive: Keeping adhesive at the recommended temperatures is important to ensure proper performance. Adhesives that are too cold or too hot will affect coverage rates and the performance of the adhesive. During winter applications, hot boxes and heated blankets should be used to keep the material between 70°F and 90°F.

For more information about two-component low-rise adhesives, please contact Austin Kulp.