Which factor can lead to fish eyes during the painting process?

One of the key factors that can lead to fish eyes during the painting process is poor surface preparation. Proper surface preparation is crucial because it ensures that the paint adheres well to the substrate. If the surface is not adequately cleaned or is contaminated with oils, waxes, or silicones, fish eyes can occur. These are small blemishes that appear on the surface of the paint finish, creating an undesirable effect.

Effective surface preparation typically involves thorough cleaning, sanding to create a good mechanical bond, and possibly the use of a solvent wipe to remove any contaminants. When these steps are neglected or poorly executed, it can compromise the quality of the paint application, leading to issues such as fish eyes.

The other options, while relevant to the painting process, do not directly correlate with the specific issue of fish eyes. Using a high-quality primer enhances the bonding properties of the paint, and having the correct paint-to-hardener ratio ensures optimal curing, while low humidity can affect drying times but isn't a direct cause of fish eyes.