CSLB C-39 Roofing ContractorLow-Slope RoofingEasy
A roofer is completing seams on a fully adhered EPDM membrane roof. Which material is used to permanently bond the overlapping edges of adjacent EPDM sheets together?
- ASeam splice tape applied over a seam primer
- BCold-process asphalt mastic only
- CHot-air welding with a mechanical welder
- DTorch-applied modified bitumen
Show answer & explanationAnswer & explanation
Correct answer: A. Seam splice tape applied over a seam primer
EPDM is a thermoset material that cannot be heat-welded like TPO or PVC. Seams are joined using a seam primer (which cleans and activates the surface) followed by a butyl-based seam splice tape.
Why the other options are wrong
- B. Mastic alone is insufficient and not the standard seaming method for EPDM.
- C. Hot-air welding is used for thermoplastic membranes like TPO/PVC, not thermoset EPDM.
- D. Torching is used for modified bitumen, not EPDM.
EPDM Seam Splice Tape
A butyl-based adhesive tape, applied after seam priming, used to bond overlapping EPDM sheet edges since EPDM cannot be heat-welded.
- EPDM is a thermoset rubber, unlike thermoplastic TPO/PVC
- Seam primer cleans and prepares the surface before tape application
- Improper priming is a leading cause of EPDM seam failure
Memory trick: EPDM won't melt, so we PRIME then TAPE it.