CSLB C-39 Roofing ContractorLow-Slope RoofingMedium
A specification requires an elastomeric roof coating to achieve 24 dry mils thickness. The coating has 60% solids by volume. How many wet mils must be applied to achieve the required dry film thickness?
- A14.4 wet mils
- B36 wet mils
- C40 wet mils
- D24 wet mils
Show answer & explanationAnswer & explanation
Correct answer: C. 40 wet mils
Wet mils = dry mils ÷ % solids by volume = 24 ÷ 0.60 = 40 wet mils. This accounts for the volume lost as solvent or water evaporates during curing.
Why the other options are wrong
- A. This is the reverse calculation (dry mils from wet), not what's requested.
- B. Miscalculated ratio; does not match the formula.
- D. Would only be correct if solids content were 100%.
Wet Mil to Dry Mil Conversion
Formula relating applied wet coating thickness to final cured dry film thickness based on percent solids by volume.
- Dry mils = wet mils × % solids
- Wet mils = dry mils ÷ % solids
- Critical for meeting warranty coating thickness specs
Memory trick: Divide dry by solids to find the wet.