CSLB C-39 Roofing ContractorLow-Slope RoofingMedium
An elastomeric roof coating is applied at 24 dry mils and loses approximately 3 mils per year due to UV exposure and weathering. The manufacturer recommends recoating once thickness drops to 12 dry mils. In how many years should the recoat be scheduled?
- A8 years
- B4 years
- C6 years
- D3 years
Show answer & explanationAnswer & explanation
Correct answer: B. 4 years
The coating can lose (24 − 12) = 12 mils before reaching the minimum. At 3 mils/year loss rate, 12 ÷ 3 = 4 years until recoating is needed.
Why the other options are wrong
- A. This overestimates the coating's service life beyond the calculated threshold.
- C. This would require an unrealistically low loss rate.
- D. This underestimates the allowable mil loss before recoating.
Coating Recoat Interval Calculation
A method for scheduling recoat maintenance by dividing the allowable mil loss (initial minus minimum thickness) by the annual wear rate.
- Formula: (Initial mils - Minimum mils) ÷ Annual loss rate
- UV exposure and weathering cause gradual mil loss
- Manufacturers specify minimum functional mil thickness
Memory trick: Subtract, then divide, to find when to re-hide.