Blowing

Description

Large rounded air bubbles or blisters, usually occurring in the area of seams and boxed in corners, or over heavily filled plastic surfaces.

Cause

Air trapped beneath the paint expands, resulting in the detachment of the paint film from the substrate. This frequently results from:

1. Poor application of filler, stopper or primer resulting in entrapped air.
2. Poor feather edging of chipped film.
3. Bridging of seams and boxed corners by the paint film.
4. Porosity and air pockets in the primer due to inferior or insufficient thinner, the compressed air pressure too high, or dry spraying.
5. Failure to prepare and seal substrate correctly, especially when spraying GRP.
6. Excessive application of heat during drying.

Prevention

1. Ensure correct application of filler, stopper or primer.
2. Feather edges of chipped film properly.
3. Avoid heavy paint application and ensure that the film penetrates into seams and boxed corners.
4. Always use recommended thinner and correct spraying techniques. Apply primers in thin web films.
5. Examine the substrate for porosity, especially for gel coat bubbles in GRP. Prepare and seal carefully.
6. Avoid excessive application of heat during drying.

Rectification

The paint must be removed to the depth of the bubble, any underlying defect remedied and the area repainted.