Cause
Liquid solvent (thinners/reducers) becomes "trapped" in the paint film when the surface layer skins over too quickly, preventing their evaporation into the atmosphere. Solvents that vaporize within the paint film leave bubbles, pinholes or craters as they push through and "pop" the surface. Solvents can be trapped due to:
- Thinner/reducer evaporating too fast for spraying conditions
- Inadequate flash time between coats
- Excessive film thickness or "piling on" of heavy/wet coats
- Too much air movement causing surface to "skin over" before solvents evaporate
- Excessive purge/flash time before force drying.
Repair
- Allow finish to thoroughly dry/cure, sand smooth and refinish. Inspect surface carefully to ensure all craters have been removed.
- Severe popping will require removal of the affected film. Prime, seal and recoat, as necessary.
Prevention
- Select recommended thinner/reducer based on temperature, humidity, air movement and size of repair
- Allow for proper flash time between coats.
- Avoid "piling on" or double wet coats.
- Restrict air movement over the surface being painted.
- Avoid extended purge/flash time before force drying.