Surface Preparation, Painting and Finishing
Surface Preparation, Painting and Finishing tests the steps that make a repair durable and invisible: cleaning, sanding, masking, priming, sealing, colour matching, blending and polishing. Exam questions often ask why a defect appeared or which product and grit to use.
Core rules
- Clean with the correct degreaser before sanding; silicone, wax and oil cause fish eyes and poor adhesion.
- Feather-edge repairs; use a primer suited to bare metal, plastic or filler, and sand primer with the recommended grit.
- Mask thoroughly; use tack cloth just before painting and keep the gun clean.
- Mix products by the stated ratio and use the correct thinner and pot life.
- Apply basecoat to hiding, then clearcoat within the specified window; blend into adjacent panels.
- Control booth temperature, gun pressure and distance; maintain a consistent overlap.
Worked example
A repaired door is to be blended into the rear door. The repairer cleans and sands with 600-grit, applies primer to bare areas, seals, then applies basecoat in thin coats, fading the colour into the adjacent panel. Clearcoat is applied over the blend area, then the finish is polished. Reasoning: a gradual blend hides the colour transition and avoids a hard edge.
Traps
Do not sand through a clearcoat edge without feathering. Do not use a contaminated gun or old thinner. Do not spray too dry or too wet; dry spray and runs are both defects. Do not polish fresh paint before it has cured.