Here's a compiled/edited/abridged How-to I've pulled together from a few sites:
- Wash and clean the area to be repaired first with soap and water, and then with a wax and grease removing solvent like DuPont's Prep-Sol, First Kleen, tar and bug remover, or mineral spirits.
- Repair any heavily damaged areas like rust, holes, or dents using coarse sandpaper and the appropriate body fillers, rust treatments, fibreglass patches or welded metal to restore the basic contour of the damaged area. (Details on these procedures are too involved for this forum)
- Sand and prepare the surface for primer. Wet sand the area to be repaired with medium grit paper (220 grit to 320 grit). "Featheredge" the repair area to have a smooth transition of the edge of the repair using finer papers, working your way up to 500 grit.
- Clean the area to prepare it for primer with a cleaning solvent like DuPont's Final Kleen, or a tack cloth at minimum.
- Mask off any area that you do not want to get primer or paint on. Use a good quality automotive masking tape and paper to cover out 18" or so. Do not mask right up to the actual repair so as to allow room to blend into the existing finish, or mask at a natural dividing body line like the edge of the panel.
- Spray primer on all bare metal and/or fibreglass surfaces and overlap onto the surrounding area with several coats of primer. On very small area's, try making a stencil out of cardboard with the cutout slightly larger than the area to be primed. Hold this stencil 1" above the surface while spraying the primer to direct it only on the needed area, yet still blending in around the edge. Avoid spraying right up to the edge of any masking tape. Let the primer dry for 2 to 3 hours.
- Wet sand the primer and surrounding area to prepare it for paint with 400 grit to 600 grit paper. If blending, wet sand the area where the paint will be blended into surrounding area with 1000 grit paper.
- Clean the surface again with Final Kleen or tack cloth to remove any sanding residue or other contamination from the surface to be painted.
- Spray your paint color on the repaired area, using light coats (especially at first). Apply 4 to 6 coats of color, waiting about 10 minutes in between each coat. Don't rush it and don't spray heavy coats. It will take the first 2 to 3 coats to completely cover the primer, then apply 2 to 3 more.
- If clearcoating, let the paint color dry for about 30 minutes and then spray 2 to 3 medium coats of clear lacquer. Either extend each coat of clear beyond the previous coat to allow for a tapered blend edge, or sand the entire panel with 1200 grit paper and clearcoat the entire sanded area. Let dry for 8 to 12 hours depending on the temperature.
- Depending on the results so far, lightly wet sand the repair with 1000 grit up to 2500 grit to remove any "orange peal", overspray, or rough areas.
- Polish smooth with rubbing or polishing compound to obtain a high gloss.
