Paint defects
Wet film failures
Sagging
Description
Sags are the downward movement of a coat of paint which appear soon after application and before setting, which results in an uneven area with a thick lower edge. They are usually apparent on local areas of a vertical surface and in severe situations may be described as curtains.
Probable causes
Over-application of paint, excessive use of thinners, incorrect (lack of) curing agent or poor workmanship. Could in extreme circumstances be a formulation problem.
Consequences
Poor appearance, possible cracking
Repair
While the paint is still wet, brush out runs and sags, although this may not result in an acceptable appearance. When the paint has dried, abrade and clean defective areas and apply overall coat or spot repair as necessary.
Prevention
Use correct application technique with suitably formulated products.
Dry spray
Description
Rough and uneven finish to the surface of the paint film where the particles are insufficiently fluid to flow together and are often poorly adhered.
Probable causes
Incorrect spray application, i.e. gun distance. Also associated with fast drying products and too high application temperature.
Consequences
Poor appearance, poor adhesion, loss of gloss
Repair
Abrade and remove any loose dry spray and reapply paint.
Prevention
Use correct application equipment and techniques. Use a slower drying solvent or solvent blend. Follow recommended application procedures.
Fish eye
Description
Small circular areas of substrate that are exposed through the applied coating immediately after application and which have at their centre a source of contamination.
Probable causes
Surface contamination in the form of small spots of wax, silicone, grease or particles from contaminated compressed air.
Consequences
Poor appearance
Repair
Abrade the affected area, degrease and reapply the coating system. Can be difficult to repair.
Prevention
Thoroughly degrease the surface and maintain equipment.
