CSLB C-39 Roofing ContractorLow-Slope RoofingMedium
A crew is installing a self-adhered SBS modified bitumen base sheet over a primed concrete deck. What is the primary purpose of applying asphalt primer to the concrete before installing the self-adhered membrane?
- ATo fireproof the deck surface
- BTo increase the overall R-value of the roof system
- CTo improve adhesion of the membrane's adhesive backing to the porous substrate
- DTo act as the primary vapor retarder for the assembly
Show answer & explanationAnswer & explanation
Correct answer: C. To improve adhesion of the membrane's adhesive backing to the porous substrate
Concrete decks are porous and can absorb moisture and volatiles that reduce adhesive tack; primer seals the surface and promotes proper bonding of the self-adhered membrane's factory-applied adhesive backing.
Why the other options are wrong
- A. Primer is not a fire-rated coating and does not serve fireproofing purposes.
- B. Primer has negligible thermal resistance and does not add R-value.
- D. Vapor retarders are separate components, not achieved through asphalt primer alone.
Self-Adhered Membrane Priming
Asphalt primer is applied to porous substrates like concrete before installing self-adhered membranes to promote proper adhesive bonding.
- Seals porous concrete surface
- Improves tack of self-adhered backing
- Must be fully cured/dry before membrane installation
Memory trick: Prime the porous deck so the sticky sheet sticks.