CSLB C-39 Roofing ContractorLow-Slope RoofingMedium
A contractor is installing fully adhered EPDM membrane using bonding adhesive rated to cover 60 square feet per gallon per surface, applied to both the substrate and the underside of the membrane. How many gallons of bonding adhesive are needed for a 3,000 sq ft roof section?
- A100 gallons
- B75 gallons
- C150 gallons
- D50 gallons
Show answer & explanationAnswer & explanation
Correct answer: A. 100 gallons
Because bonding adhesive is applied to two surfaces (substrate and membrane underside), the effective coverage rate is halved to 30 sq ft per gallon. 3,000 sq ft ÷ 30 sq ft/gal = 100 gallons required.
Why the other options are wrong
- B. 75 gallons does not match the correct halved coverage calculation.
- C. 150 gallons overestimates the adhesive requirement.
- D. 50 gallons assumes 60 sq ft/gal without accounting for two-surface application.
Bonding Adhesive Coverage Calculation
Fully adhered EPDM bonding adhesive is applied to both the substrate and membrane, so effective coverage per gallon is half the single-surface rating.
- Rated coverage (e.g., 60 sq ft/gal) applies per single surface
- Two-surface application halves effective coverage to 30 sq ft/gal
- Always verify manufacturer's actual coverage tables for job estimating
Memory trick: Two coats halve the gallon's reach.