Paint Defects
Diagnosis first
Every defect has a cause; sanding it out and repainting without removing the cause reproduces it. Identify the defect, the stage it appeared (primer, base or clear) and the conditions: temperature, gun setting, contamination.
Common defects
- Runs and sags: too much material, gun too close, too slow, coat too wet.
- Orange peel: paint too thick, pressure too low, gun too far, reducer too fast.
- Dry spray: gun too far, pressure too high, reducer too fast, panel too hot.
- Mottling: metallic flake orientation wrong; uneven gun distance or overlap.
- Solvent pop and blisters: trapped solvent, coats too wet, flash-off too short, heat applied too soon.
- Fish eyes: silicone or oil contamination.
- Pinholes: filler porosity or trapped air in the bodywork.
- Peeling and cracking: poor adhesion, over-thick film, wrong primer.
- Sanding scratches: grit too coarse under the topcoat.
Worked example
A freshly sprayed bonnet shows circular craters with raised rims: fish eyes. The source is usually silicone from polish, a contaminated rag or an aerosol in the booth. Clean with fresh panel wipe, replace the rags, add fish-eye eliminator only as directed, and test on a card. If severe, strip and start again.
Traps
- Adding extra additive instead of finding the contamination.
- Wet-sanding a run and polishing without letting the film cure.
- Repainting in the same cold booth that caused the last defect.
- Sanding scratches with finer paper instead of priming and blocking.