Blisters appear as swellings on the surface of the paint and vary considerably in both size and density.
Coarse blisters, larger than 1.5mm in diameter, generally occur in patches, although they may also be found in isolation.
Fine blisters, typically from 0.5mm rings, meandering lines or in the shape of a finger print.
Blisters in the colour coat are generally more prominent than those occurring between paint and substrate.
Moisture or contaminants trapped under the surface. This may result from:
a) Inadequate surface cleaning, leaving residual moisture or contaminants such as oil, industrial pollutants or grease from finger tips.
b) Incompatible materials or the use of non-recommended thinners.
c) Insufficient thickness of paint leading to increased permeability.
d) Water permeating both newly applied and aged films. Exposure to rain or high humidity before the finish is fully hardened increases the risk of blisters caused by permeation.
a) Protect vehicle surfaces when in store, and clean surfaces scrupulously before spraying.
b) Use only top quality recommended and approved materials.
c) Follow the correct spraying processes.
d) Avoid exposure to moisture and extreme temperature changes until the finish is fully hardened.
Establish the depth and cause of the blister by pricking out with a pin and examining under a low power magnifying glass.
Where the blisters occur between paint layers, the affected area may be sanded down to a sound surface and repainted.
In more severe cases, or where the blisters occur between the undercoat and the substrate, strip down to the substrate and repaint.