CSLB C-33 Painting & DecoratingCoating ApplicationMedium
A painting contractor is applying a clear lacquer finish to custom-built cabinetry. After the first coat, the contractor notices small, crater-like depressions with a raised edge, resembling 'fisheyes', appearing on the surface. Which of the following is the MOST probable cause of this defect?
- AThe ambient temperature was too low, slowing solvent evaporation.
- BContamination on the substrate surface, such as oil or silicone.
- CThe lacquer was applied too heavily in a single coat.
- DInsufficient sanding between coats, creating an uneven surface.
Show answer & explanationAnswer & explanation
Correct answer: B. Contamination on the substrate surface, such as oil or silicone.
Fisheyes are a common coating defect characterized by small, crater-like depressions formed when a coating fails to wet out a contaminated surface. Silicone, oil, wax, or grease are typical contaminants that cause the surface tension of the liquid coating to break, leading to these craters.
Why the other options are wrong
- A. Low temperature would primarily slow drying and potentially cause blushing or sags, not fisheyes.
- C. Applying lacquer too heavily might cause sags, runs, or solvent pops, but not typically fisheyes.
- D. Insufficient sanding might lead to poor adhesion or an uneven appearance, but not the specific crater-like defect of fisheyes.
Fisheye Defect
Fisheyes are crater-like depressions in a coating film, often caused by surface contamination (e.g., silicone, oil) that prevents proper wetting and flow.
- Caused by surface tension differences due to contaminants.
- Common in automotive and fine finishing due to silicone presence.
- Requires thorough surface cleaning or addition of a fisheye eliminator.
Memory trick: Fisheyes see a dirty surface, refusing to spread evenly.