CSLB C-33 Painting & DecoratingCoating ApplicationHard
A painting inspector is performing a final quality control check on a newly applied two-coat epoxy system on structural steel. The specification requires a dry film thickness (DFT) of 6-8 mils per coat, for a total of 12-16 mils. Using a Type 2 electronic dry film thickness gauge, the inspector takes several readings. One reading shows 10 mils for the first coat and 5 mils for the second. What is the most appropriate interpretation of this result?
- AThe second coat is acceptable, but the first coat should have been thinner.
- BThe first coat is too thick, and the second coat is too thin, requiring remediation.
- COnly the total DFT matters, so the individual coat thicknesses are irrelevant as long as the total is correct.
- DThe total DFT is within specification, so no action is required.
Show answer & explanationAnswer & explanation
Correct answer: B. The first coat is too thick, and the second coat is too thin, requiring remediation.
While the total DFT (10+5=15 mils) falls within the 12-16 mil range, individual coat thickness specifications are crucial for multi-coat systems. Applying a coat too thick can lead to solvent entrapment, cracking, or poor intercoat adhesion, while applying it too thin compromises protection. Both coats must meet their individual specified ranges.
Why the other options are wrong
- A. Incorrect. The second coat is below the minimum specification, which is not acceptable.
- C. Incorrect. Individual coat thicknesses are very important. They ensure proper curing, prevent defects, and guarantee the protective properties designed for each layer.
- D. Incorrect. Although the total DFT is within range, individual coat thicknesses are also critical for performance and can lead to defects if not met.
Dry Film Thickness (DFT) Specification
DFT specifications define the required thickness of a coating after it has dried. For multi-coat systems, both individual coat DFTs and total system DFT are critical for performance and longevity.
- Too thin a coat compromises protection.
- Too thick a coat can lead to cracking, solvent entrapment, or slow curing.
- Individual coat DFTs are as important as total DFT for multi-coat systems.
Memory trick: Each coat's a must, for total trust.