CSLB C-33 Painting & DecoratingCoating ApplicationHard
A painting contractor is applying a high-build epoxy coating to a concrete floor at a specified dry film thickness (DFT) of 10 mils. The manufacturer's data sheet states the coating has 80% solids by volume. If the contractor applies 160 square feet per gallon, what is the approximate wet film thickness (WFT) being applied?
- A10 mils
- B8 mils
- C16 mils
- D12.5 mils
Show answer & explanationAnswer & explanation
Correct answer: D. 12.5 mils
To calculate WFT from DFT and % Solids by Volume, use the formula: WFT = DFT / (% Solids by Volume). In this case, WFT = 10 mils / 0.80 = 12.5 mils. The coverage rate (160 sq ft/gal) is extraneous information for calculating WFT from DFT.
Why the other options are wrong
- A. Incorrect. This is the target DFT, not the WFT.
- B. Incorrect. This would be the DFT if 80% solids were applied at 10 mils WFT (10 * 0.8 = 8).
- C. Incorrect. This would be the WFT if DFT was 12.8 mils (12.8 / 0.8 = 16) or if 62.5% solids was applied at 10 mils DFT (10 / 0.625 = 16).
Wet Film Thickness (WFT) Calculation
Wet Film Thickness (WFT) is the thickness of a coating immediately after application, calculated by dividing the desired Dry Film Thickness (DFT) by the coating's percent solids by volume.
- WFT = DFT / (% Solids by Volume).
- WFT is always greater than or equal to DFT.
- Measured with a wet film comb/gauge during application.
Memory trick: WFT is DFT divided by solids, a clear path to follow.