Blistering (Humidity)

Causes

1. Moisture trapped between primer and substrate, or between primer and topcoat
2. Contamination of the surface by oil / grime
3. Absence or lack of primer with good anti-corrosive properties
4. Insufficient film build
5. Soluble salts from sanding water and metal pre-treatments
6. Rapid changes in surface temperature
7. Wide differences in temperature between substrate and coating
8. Poor quality thinner

Prevention

1. All substrates should be clean, contaminant free and totally dry before the painting process commences
2. Compressed air supply should be clean and moisture free
3. The paintshop maintained at correct operating temperature (68°F – 72°F) substrate allowed to reach paintshop temperature before painting
4. Use of recommended primer at required film thickness
5. Flatting water should be changed regularly
6. Correct use of recommended thinners
7. Allow paint to dry thoroughly before exposing to humidity

Rectification

1. In the case of extensive blistering, paint must be removed down to a sound surface, then repainted
2. Localised blistering may be flatted, re-primed and topcoated