Painting and Refinishing
This domain covers surface preparation, primers, fillers, basecoat, clearcoat, spray equipment, booth conditions and defect correction. The exam tests process control, mixing ratios and finish quality.
Core rules
Preparation determines adhesion: clean, degrease, sand, remove rust and mask correctly. Primer protects and provides adhesion; filler levels minor imperfections. Basecoat provides colour and clearcoat provides gloss and UV protection. Mix according to the manufacturer's ratio by volume, not by guesswork. Use the specified thinner, pot life and flash-off time. HVLP spray guns transfer more material and reduce overspray. Booth temperature, humidity and cleanliness control defects.
Worked example
A clearcoat is specified at 4:1 by volume with 10 percent thinner added to the mixed paint. For 800 mL of clearcoat, add 800 / 4 = 200 mL hardener. The paint-plus-hardener total is 1000 mL; 10 percent thinner is 100 mL, giving 1100 mL sprayable material. If the pot life is 60 minutes, mix only what can be sprayed within that time.
Traps
Measuring by weight when the ratio is by volume; adding too much thinner and causing runs; spraying outside the recoat window; and confusing orange peel with solvent pop. Orange peel is a rough, pebbled surface from poor atomisation or too-fast thinner; solvent pop is trapped solvent blistering. Clean the gun immediately after use.