Moisture blisters can appear in various forms, sizes, areas, and densities. Blistering can occur between individual layers or underneath the entire coating structure. Once sealed, the coating film causes the moisture blisters to gradually disappear in dry weather.

Causes

1. Surface not cleaned: The surface to be coated (filler, bare metal, etc.) was not adequately cleaned. Contamination caused by soluble salts in dirty water used for sanding or cleaning, or sweat from hands (forming visible "string pearl" moisture blisters), leads to long-term moisture effects and coating defects.

2. Insufficient drying after wet sanding: Moisture blisters can also occur if polyester materials are wet sanded and insufficient time is allowed for moisture to evaporate before primer and topcoat application.

Prevention

1. Clean the surface: The surface must be thoroughly washed with clean or hot water before coating. Use a silicone and tar remover (universal cleaner) or a metal cleaner for complete cleaning.

2. Ensure moisture evaporates: All moisture must be allowed to evaporate thoroughly after wet sanding.

3. Use dry polyester materials: Only completely dry polyester materials should be used.

Repair

Sand down the coating in the blistered area to the substrate and reapply primer and topcoat. If necessary, strip and repaint the area, ensuring the correct primers and fillers are used during reapplication.