Rust is an insidious problem for car owners. Left unchecked, it can seriously damage the metal surfaces of a car and greatly reduce its resale value. The most important thing you can do to minimise rust damage is to inspect your vehicle regularly for indications of rust. Repairing rust spots under the vehicle do not require repainting. Repairing rust on painted surfaces requires additional steps to repaint the affected areas. Act quickly to eliminate small rust spots and repair the damaged area before the rust spreads and causes major damage that requires professional attention.
Brush or scrape away loose fragments of rust and debris with your wire brush. Begin brushing near the centre of the affected area and brush outward. Then reverse the process and brush inward until all loose pieces of rust are removed.
Apply a small amount of isoproply alcohol to the rusted area, and rub the area with coarse sandpaper until all visible rust is removed. Use a clean, dry cloth to wipe the area.
Apply rust neutraliser to the affected area according to the manufacturer's instructions. Let the neutraliser dry for the required amount of time, which may be several hours, before applying a second coat. Let the neutraliser work overnight.
Apply a coat of automotive paint primer to the area. Follow the manufacturer's directions exactly. After the primer has dried, wipe it with a clean, damp cloth and then dry with a clean cloth. Apply a second coat of primer if needed.
Apply isopropyl alcohol to the rust spot with a clean cloth. Rub with the affected area with coarse sandpaper until all loose rust fragments and paint fragments are removed. Wipe the area with a clean cloth.
Apply rust solvent according to manufacturer's directions, then rub with coarse sandpaper to remove the remaining visible rust from the area. Start at the outer edge of the rusted area and work your way toward the centre. Create a rust-free area surrounded by a rust-free paint surface.
Cut a hole in the newspaper or brown craft paper roughly the size of the affected area with a utility knife. Tape it to the vehicle with the masking tap, centring the hole over the area you cleaned with sandpaper.
Apply two or three coats of primer to the cleaned area according to the manufacturer's instructions for application. Be patient and allow sufficient time between primer applications for each coat to dry.
Sand away excess dried primer by rubbing the area lightly with fine sandpaper.
Apply automotive glazing putty to the primed area using a plastic spreader. The putty should be applied smoothly and fill any pinholes, scratches or small dings on the metal surface. Allow the putty to dry, and wipe the area clean with a cloth.
Apply automotive touch-up paint, blending it with the surrounding paint. It may take two to three applications to cover the spot. Follow the manufacturer's instructions on drying time before adding coats.
Add a final clear coat layer to the paint. Apply the clear coat according to the manucacturer's directions, and allow it to dry as directed.
Apply a high-quality auto wax to the newly painted spot and surrounding areas.
Always wear a mask and protective eye wear when sanding, painting or using chemical solvents. Exact paint colour matches of touch-up paint for each make and model of vehicle can be purchased at auto supply stores. Many cars have the colour identified on a plate under the hood. Some touch-up paints are available in both brush on and spray versions. The finished surface of the glazing putty should be smooth and even with the unaffected surface of the vehicle. All pinholes and scratches must be filled to ensure full and smooth paint coverage.