IV. The Repair Process
Part 1: Preparation: Sand and Wash
Wet sand: Wet sand the area you are going to spray with 500 grit paper. This is going to smooth out the surface, and create good adhesion with the primer. You can use the 500 grit to smooth out scratches or a scuffed area if they aren’t too deep. If it is a large area like a door or quarter panel, consider using a dual action random orbital sander, but you can always do it by hand. For most repairs that are smaller, you can wet sand by hand.
Pro Tip: Make sure to sand away all rust, chips, and any loose paint. Sand enough to smooth out scrapes, but if they are too deep, use spot putty (#2 below). Lightly scuff the nearest surrounding clear coated paint to improve the adhesion. Feather your more heavily sanded areas into the lightly sanded areas, so they meet smoothly.
Optional spot putty: If you have deep scratches that sanding can’t remove, use a glazing/spot putty like 3M 907 Bondo, an easy-to-use, sandable spot putty to fill them in.
Apply the spot putty using a body filler spreader tool. Apply a uniform layer to fill in the scratches and let it fully dry. Then wet sand (500 grit paper) the spot putty until smooth, contouring your hand to the shape of the panel, and using even pressure so you don’t create an uneven surface. Consider using a foam or wood block to wrap the sand paper around for consistency.
Wash thoroughly: Wash the entire area with soap and water; this is an important step to remove any contaminants such as wax, grease, and heavier road grime that will ruin the job. Dawn dishwashing detergent works well. Dry the area thoroughly, and if necessary, use a hair dryer on the high setting to drive any water out of cracks or crevices. Compressed air also works great to drive out water and dry the area.
Mask the area: Apply automotive masking tape to create a boundary some distance away from the repair. Consider the area you want to prep to be large enough to cover the repair, and about 10-15% more area as a buffer, to feather the repair into. Always tape and cover door handles, windows, antenna openings and the like. Use tape at the edge, and use plastic or paper beyond to protect all the nearby paint from overspray (especially if you are outside).
Pro tip: Try to paint to a panel line, a molding transition, a door boundary, or an angled surface, so that the repair finish blends into the rest of the finish invisibly. Solution: Don’t just tape any region around your repair, consider the area you are going to tape carefully, and have it follow a boundary line that helps the repair blend better. This will avoid having a noticeable paint line in the middle of a body panel.
Degrease: Degrease the area with a prep wipe. This is an important final step to eliminate any remaining grease from your hands or other contaminants, which will show up as fisheyes in the paint finish, and require resanding and repainting.
Tack cloth: Wipe down the entire area with a tack cloth to remove dust.