Defects of paint coatings affecting durability
Cratering in Coatings
Description: Macroscopic round depressions in the coating.
Causes:
- Excessive coating thickness
- Insufficient surface preparation before painting; use of inappropriate degreasers
- Poor cleaning of compressed air used for spraying
- Presence of airborne contaminants, e.g., from polishing compounds
Boiling in Coatings
Description: Small, partially burst bubbles on the coating surface.
Causes:
- Excessive coating thickness
- Insufficient flash-off time between layers and before oven curing
- High coating viscosity
- Use of hardeners and solvents unsuitable for application and curing temperature conditions
Wrinkling in Coatings
Description: Small folds throughout the coating thickness, resembling frog skin.
Causes:
- Incompatibility between coating layers or with the substrate; solvent from the top layer penetrates sensitive substrates and dissolves them
- Incorrect timing between application steps
Cracking in Coatings
Description: Formation of splits in the dried coating.
Causes:
- Excessive coating thickness
- Low coating viscosity
- High spray pressure or too close spraying distance
- Unsuitable application conditions (low temperature, high humidity)
Contamination in Coatings
Description: Foreign particles on or within the coating.
Causes:
- Poor cleaning of the surface
- Dirty spray gun
- General contamination of the painting area
- Insufficient filtration of coating material
- Static charge on the painted part
Blistering in Coatings
Description: Small pinpoint bubbles filled with air or water, ranging from 0.1 to 4 mm.
Causes:
- Moisture on the surface or in the air
- Coating lacks water resistance or is insufficiently dried
- Excessive temperature during curing
Poor Adhesion
Description: Coating does not adhere or adheres poorly to the surface.
Causes:
- Contaminated substrate
- Excessive coating thickness
- Violation of application technology or unsuitable conditions
- Incompatibility between coatings or with the substrate
- Insufficient substrate roughness
Important Notes for Defect Prevention
- It’s always easier to prevent defects than to fix them.
- Coatings with durability-affecting defects must be removed.
- Repaired coatings are generally inferior to original finishes.
- Two-component coatings are easier to repair.
- Do not use solvent for degreasing.
- Follow the application technology strictly.
- When in doubt, take extra precautions.
- Enamel does not correct substrate or surface preparation defects.
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