CSLB C-39 Roofing ContractorLow-Slope RoofingEasy
A roofer is installing a fully adhered EPDM membrane and applies EPDM splice adhesive to both the membrane and flashing surfaces before joining them. Per typical manufacturer instructions, what must the applicator do after coating both surfaces and before pressing them together?
- AImmediately press the surfaces together while the adhesive is still wet
- BWait until the adhesive is completely dry and hard before joining the surfaces
- CApply a second coat of adhesive over the first before it dries at all
- DAllow the adhesive to flash off until it is tacky but not wet, forming no strings when touched
Show answer & explanationAnswer & explanation
Correct answer: D. Allow the adhesive to flash off until it is tacky but not wet, forming no strings when touched
EPDM splice adhesive (contact adhesive) must flash off to a tacky, string-free state before the two surfaces are mated; bonding too wet traps solvent and weakens the bond, while waiting until fully dry prevents adhesion altogether.
Why the other options are wrong
- A. Wet adhesive traps solvents and produces a weak, bubbled bond.
- B. Fully dried contact adhesive will not bond to another dried surface.
- C. Recoating before flash-off just adds more solvent that must escape, delaying proper cure.
EPDM Splice Adhesive Flash-Off
A contact adhesive used to bond EPDM seams that must partially dry (flash off) to a tacky, non-stringy state before the two coated surfaces are pressed together.
- Contact adhesives bond best when tacky, not wet or fully dry
- Test by touching with a dry finger — no strings or transfer means ready
- Roll the seam after bonding to ensure full contact
Memory trick: Tacky, not wet — press when the strings won't stretch.