Surface Preparation, Masking, and Paint Mixing
Surface preparation
Wash, degrease, and sand before painting. Know grit progression: 80–180 for primer prep, 320–400 for topcoat prep, and finer for blend panels. Feather edges to blend repairs. Use tack cloths to remove dust. Primers: etch primer for bare metal, epoxy primer for corrosion protection, and primer surfacer for filling and sanding.
Masking
Use masking tape and paper to protect adjacent panels, glass, trim, and openings. Masking should follow panel edges and leave a soft edge for blending. Know that tape should not be left too long (adhesive transfer) and that masking must prevent overspray without trapping solvent.
Paint mixing
Understand mixing ratios (e.g., 4:1, 2:1, 3:1) and that ratio is by volume, not weight, unless specified. Add hardener and reducer per the product data sheet. Pot life is the usable time after mixing - exceeding it causes poor cure. Use a mixing stick and graduated cup. Viscosity affects spray pattern; reducer adjusts it for temperature.
Traps and rule of thumb
Trap: mixing by weight when the ratio is by volume. Trap: adding extra hardener to speed cure - it causes brittleness and poor adhesion. Rule of thumb: follow the product data sheet exactly - ratio, pot life, and recoat window are not negotiable.