01
Coating
Chipping
Fragments of the coating flaking off in sheets — poor adhesion between coats, poor substrate preparation or a mismatched paint system.
Cause
- Poor adhesion between coats — the paint chips off in sheets rather than in spots
- Top coat too hard and brittle relative to the other coats in the system
- Wrong primer for the substrate — a particular problem on galvanised steel and aluminium
- Insufficient degreasing of the substrate before painting
- Abrasive paper with too fine a grit — a substrate that is too smooth reduces mechanical adhesion
- Failure to observe flash-off times between coats
- Thinner too fast, causing dry spray or condensation
- Wrong paint system, unsuitable for the substrate in question
- No flex additive when painting plastic parts — bumpers and other plastic components flex and bend while driving, and a rigid paint film cracks and chips with every deflection
- Incorrectly selected primer for plastics — some plastics (PP, TPO) require a special adhesion promoter, without which the paint has no mechanical adhesion at all
Prevention
- Use primers and filler primers that comply with the technical data sheet and suit the substrate
- For plastic parts, use flexible 2K systems
- Degrease only with the recommended cleaners, using clean cloths
- Wash the part with warm soapy water before degreasing — remove all contamination
- Sand the edges of the repair area with abrasive paper of the correct grit
- Observe the flash-off and drying times given in the technical data sheet
- Apply coats at the recommended film thickness and at the correct pressure
- Use the correct thinner for the temperature and working conditions
- On plastic parts, always apply a dedicated plastic adhesion promoter before painting
- For paints applied to bumpers and flexible parts, add a flex additive in the proportions given in the technical data sheet — a flexible paint film moves with the substrate instead of cracking
- Remember that different plastics (PP, ABS, TPO, PC) require different preparation systems — always identify the type of plastic before selecting products
Repair
- Repair small chips as soon as possible, before corrosion destroys the substrate and the paint system
- Minor damage: brush touch-up — clean, prime, cover with base coat and clear coat
- Extensive chipping requires full substrate preparation and repainting of the whole part
- After the repair, check the adhesion of the system — if chips keep reappearing, the problem lies in substrate preparation
- When repairing plastic parts, always use a system with a flex additive — a repair using a standard system on a bumper will end in fresh chipping the first time the part flexes