Paint Defects, Causes, and Corrections
What the exam expects
You must link each defect to its root cause and the correct repair. Learn to distinguish defects that occur during application from those caused by contamination, substrate, or environment.
Core concepts
- Runs/sags: too much material, too close, too slow a pass, or material too thin. Correct by letting cure, then sand and polish or recoat.
- Orange peel: insufficient atomization, wrong reducer, too much air pressure or too fast a pass. Correct by sanding and polishing or recoating.
- Fisheyes: silicone/oil contamination from the air line, shop, or substrate. Correct by cleaning, adding fisheye eliminator cautiously, and recoating.
- Solvent pop: trapped solvent from short flash times or heavy coats. Correct by sanding out and recoating with proper flash.
- Dry spray: gun too far, too fast, or too much air. Correct by sanding and recoating.
- Trash/dirt: booth contamination or unfiltered air. Correct by cleaning, filtering, and recoating.
- Adhesion failure/peeling: poor prep or missed recoat window.
Traps
Defect questions often present a symptom and a plausible but wrong cause. For example, offering "too much reducer" for fisheyes (real cause: silicone) or "too little air" for dry spray (real cause: too much air or distance). Always match the defect to its most direct cause.
Worked example
A freshly cleared panel shows small pinholes across the surface. That is solvent pop from trapped solvent. The correction is to allow full cure, sand the affected area, and recoat with adequate flash time and lighter coats - not simply to add more clear.
Rule of thumb: diagnose the cause before choosing the correction; recoating over an uncorrected cause repeats the defect.