CSLB C-39 Roofing ContractorLow-Slope RoofingHard
A technician is detailing a roof transition where a PVC membrane flashing will make direct, permanent contact with an adjacent EPDM membrane. What compatibility issue should the technician be aware of?
- APlasticizers in the PVC can migrate into the EPDM, causing the EPDM to swell, soften, or degrade over time
- BThere is no compatibility concern since both are synthetic single-ply membranes
- CDirect contact between the two membranes will trigger an exothermic reaction requiring a fire watch
- DEPDM will off-gas sulfur compounds that corrode the PVC's reinforcing scrim
Show answer & explanationAnswer & explanation
Correct answer: A. Plasticizers in the PVC can migrate into the EPDM, causing the EPDM to swell, soften, or degrade over time
PVC membranes contain plasticizers to keep them flexible. Over time, these plasticizers can migrate out of the PVC into adjacent EPDM, causing the EPDM to swell, soften, or otherwise degrade. A compatible separator or transition strip should be used to prevent direct contact.
Why the other options are wrong
- B. This is incorrect; a well-documented compatibility issue exists between PVC and EPDM.
- C. There is no exothermic chemical reaction between these two membrane types.
- D. There is no sulfur off-gassing mechanism causing this type of degradation.
PVC–EPDM Plasticizer Migration
A compatibility issue where plasticizers in PVC membranes migrate into adjacent EPDM rubber, causing the EPDM to swell, soften, or degrade at points of direct contact.
- PVC contains plasticizers for flexibility
- EPDM lacks plasticizers and can absorb migrating ones
- Compatible separator strips prevent direct contact at transitions
Memory trick: PVC's plasticizer leaks and makes EPDM weak.