Sure, you can lower your risk of rust by applying paint protection film to chip-prone areas like the front edge of the hood, and by frequently washing off road salt and waxing your vehicle regularly. But even then, you’re still going to get rust spots. If you ignore them, they’ll spread and turn your sheet metal into Swiss cheese in no time. However, if you deal with rust early, you can stop it from spreading and squeeze a few extra years out of your vehicle.
Mask the vehicle
Protect the entire vehicle from paint overspray with poly sheeting. If you’re painting the hood, spread poly sheeting over the engine and fenders. In door areas, cut poly sheeting to fit the door opening and tape it to the jamb. The final masking must be a foot or two away from the repair area
Sand, feather, and clean
Crack off any blistered paint with a scraper. Then sand the rust using 40-grit sandpaper. Then feather the paint edges. Use a tack rag to remove particles from the unmasked area. Then clean the sanded area and apply the paint manufacturer’s prep solvent.
If the rust has created pits in the metal, you can fill them now with body filler or wait until the epoxy primer dries and apply multiple coats of filler primer.
Prime the surface
Self-etching epoxy primer provides a strong bond to bare metal, so use it as your first coat. Spray two to three medium coats, allowing the recommended wait time listed on the label (usually 15 minutes) between coats. Wait a full hour for the epoxy to dry to the touch (longer if it’s humid outside). Sand the epoxy primer with wet 1,000-grit sandpaper. Wash with clear water and let dry. Wipe the dried epoxy primer with a lint-free cloth and apply two to three heavier coats of lacquer filler primer, allowing drying time between each coat. Let the lacquer primer dry until it’s dry to the touch—at least one hour—before sanding.
Sand drips and sags with 320-grit sandpaper. Then final-sand the entire repair area.
Spray the base coat
Holding the spray can about 12 in. away from the surface, spray the repaired area. The slower you build the color coat, the better it’ll look under the clear coat. Allow the base coat to dry, until it’s dry to the touch, at least 60 minutes. Don’t sand the base coat (especially metallic colors) unless you’ve created sags. In that case, sand lightly and then respray the touched-up areas
Add the clear coat
This is the hardest part because all clear coats run easily and that will ruin the look of your paint job. If you create a run in the clear coat, you’ll have to let it dry for at least 48 hours before attempting to fix it with fine-grit sandpaper and polishing compound. Then you’ll have to respray the sanded area. So practice spraying on a scrap piece of cardboard to get a feel for the nozzle and the speed of application.
Clean the painted area one last time with a tack rag. Then apply the first layer of clear coat so it looks wet
Buff the repair
Using an old cotton T-shirt or microfiber cloth and buffing compound, hand-buff the repaired area. Don’t use a polishing machine for this step. Wait at least 30 days before waxing.