Rust holes in an auto body panel contribute to a weakening of the car frame and present a safety hazard. The rust holes also produce drafts and are very unsightly. To fix a rust hole, a patch is installed over the hole. The project restores the panel close to its original condition. If you have auto body skills, this is a routine fix. For the amateur, however, the project will require an afternoon or more to complete.
Cut away the rusted metal surrounding the rust hole using a disc grinder and a metal cutting disc. Remove all of the rusted metal around the hole. When finished, only solid, uncorroded metal should remain.
Measure the size of the hole with a tape measure. Find the widest and longest points and add 5 cm (2 inches). Trace out a shape with these dimensions, similar to the hole you have, on a piece of sheet metal. Use a magic marker to draw the shape. With a pair of metal shears, cut out the shape to use as your patch.
Place the patch over the hole and orient it so about 5 cm (2 inches) of sheet metal overlaps onto the car surface.
Drill holes along the edge of the sheet metal, through both the sheet metal and the car metal, with a power drill and carbide bit. Make a hole about every 75 mm (3 inches).
Insert a rivet into your rivet gun and set the rivet into the holes you drilled through the sheet metal. Attach the rivet by clamping the gun closed. This will secure the sheet metal in place. Apply one rivet per hole.
Cover the sheet metal and a 2.5 cm (1 inch) area around the sheet metal with auto-repair putty or body filler using a plastic applicator card. Spread the putty evenly over the patch and onto the car surface. Let it dry for five to six hours (allow for more time on larger patches).
Sand down the putty with 80-grit sandpaper and a sanding block until the patch and surface of the car appear smooth and even.
Apply a coat of auto primer to the surface of the repair and let this dry for four to six hours or as indicated on the label of the paint. Add one more coat of primer after completely dry. Once the final primer coat is dry, apply a top coat of matching automotive-grade paint to the surface of the repair if desired.
To avoid a bump repair, place the sheet metal on the underside of the panel and apply the putty or dent filler to the outside of the car so it covers the patch from the outside.