Tiny holes in the paint finish. Pinholes are small blisters whose surface has broken during the drying process. Pinholes are often caused by trapped air, trapped solvents and trapped moisture escaping from the film.
Lack of adequate surface cleaning and surface preparation, (which will leave contaminants on the surface such as water and oils).
Incorrect gun adjustment or technique. For example the gun held too close to the substrate will result in air being "blown into" the coating.
Improper or forced drying. Fanning or forcing air across a newly painted surface can drive air into the surface. If the temperature is too warm, solvent can flash off the surface too quickly leaving pinholes behind.
Incorrect thinner used. When the solvent is too slow the solvent can get trapped below the drying film. When the solvent is too fast this forces the applicator to apply closer to the surface and can drive air into the coating.
Contaminated air lines.
Make sure surfaces to be coated are fully cleaned and degreased before application. Take great care to avoid moisture on the surface.
Use correct gun pressure, technique and gun adjustments specific for the product in question.
Make sure sufficient flash off time and drying time is left. If experiencing pinholing do not dry by fanning, blowing air.
Make sure a thinner appropriate for current booth conditions is used.
Clean air pressure lines frequently and make sure air lines are properly maintained to avoid trapped oil, moisture and dirt.