Surface Preparation, Priming, and Refinishing
Surface Preparation, Priming, and Refinishing tests substrate identification, cleaning, primer selection, and finish application. Most refinish failures are preparation failures.
Preparation
- Wash, then degrease with the specified cleaner; use a tack cloth before coating.
- Identify the substrate: steel, galvanized, aluminum, plastic, e-coat, or existing finish.
- Sand with the correct grit sequence; featheredge and remove sanding scratches.
- Do not sand through e-coat on galvanized or aluminum unless the OEM procedure allows it; bare aluminum needs the specified conversion coating or primer.
Priming and topcoat
- Epoxy primer seals and provides adhesion; urethane primer surfacer fills and sands; etch primer is for specific bare metals.
- Sealers prevent bleed-through and give uniform color; use the recommended sealer shade.
- Mix base and clear by volume, not by eye; observe pot life, flash time, and dry film thickness.
- Blend within a panel or to a natural break; control booth temperature and contamination.
Worked example
A technician sands a blend panel to bare metal and applies basecoat directly. Reasoning: bare steel needs primer for adhesion and corrosion protection, and basecoat may not hold on bare metal. Correct sequence: clean, apply epoxy primer, sand, seal, base, and clear, observing flash times.
Traps
- Using lacquer thinner as a final wipe.
- Sanding through e-coat without repriming.
- Mixing products from different systems.
- Applying clear too dry or too wet.