CSLB C-33 Painting & DecoratingCoating ApplicationMedium
A painter is applying a clear lacquer finish to custom-built cabinetry. After the first coat dries, several small, round, crater-like depressions appear on the surface, revealing the substrate beneath. This defect is commonly known as 'fisheyes.' What is the most probable cause of this issue?
- AApplying the lacquer too thickly, causing solvents to become trapped and bubble.
- BApplying the lacquer in excessively humid conditions, leading to moisture entrapment.
- CInsufficient surface preparation, leaving behind contaminants like oil, grease, or silicone.
- DUsing an incompatible thinner, causing the lacquer to separate during application.
Show answer & explanationAnswer & explanation
Correct answer: C. Insufficient surface preparation, leaving behind contaminants like oil, grease, or silicone.
Fisheyes are typically caused by surface contamination (e.g., oil, grease, silicone, wax) that prevents the coating from flowing out smoothly. The surface tension of the liquid coating is broken by these contaminants, causing it to pull away and form small craters.
Why the other options are wrong
- A. Applying too thickly usually leads to sags, runs, or solvent pops (small blisters from trapped solvent), not fisheyes.
- B. High humidity can cause blushing (a milky appearance) or slow drying, but generally not fisheyes.
- D. Incompatible thinners can cause issues like curdling or poor adhesion, but fisheyes are specifically related to surface contamination.
Fisheye Defect
Fisheyes are small, round, crater-like depressions in a wet paint or lacquer film, typically caused by surface contamination (oil, grease, silicone) that repels the coating.
- Caused by low surface tension areas on the substrate.
- Prevented by thorough cleaning and degreasing.
- Can sometimes be remedied with a 'fisheye eliminator' additive, though prevention is best.
Memory trick: Fisheyes spot the oily dot.