Once rust is present on your car, it can spread easily under the paint and cause major structural damage. Rust forms near windshields easily because of the large weatherstripping found around the windshield. Water can get trapped on the weatherstripping, allowing the water to form rust over time. Removing this rust can be difficult without removing or damaging the windshield.
Remove the weatherstripping from around the windshield if the rusted area is touching it. Just pry it up with a flat screwdriver. Sand the rusted area with 200 grit sandpaper to remove the loose pieces of rust. This also smooths the rough edges of the rust patch. Place masking tape and paper around the rust patches that have been sanded clean. Place masking paper over the entire windshield to protect it from overspray.
Spray the rust fix product on the rusted areas. This turns the rust black and bonds it together so that no more rust will spread, even if you don't remove all of the rust. Wait one full hour after spraying the rust fix before handling the areas. Keep the rust fix from coming into contact with the glass on the windshield by adding tape around the edges of the masking paper to seal the windshield completely.
Fill the rust patches with body filler. Apply a light coat of filler to any holes or low areas by spreading and smoothing the filler with a plastic squeegee. Allow the filler to dry for a full hour before handling. The windshield should still be covered with paper, but if filler gets on the glass, allow it to harden and then chip it off with your fingernail or a razor blade. Don't smear damp filler over the glass.
Sand the filler with 200 grit sandpaper until it is smooth and even with the surrounding surface. Spray a moderate coat of primer over the filler and wait 30 minutes for it to dry. Spray two thin coats of paint over the primer, waiting 15 minutes between coats. Apply two thin coats of clear coat paint over the paint, waiting 15 minutes between coats and 3 hours before reattaching any of the weatherstripping to the windshield.
Rust fix products are made by several different companies, but they all work and are used in the same manner. If rust fix, primer or paint gets sprayed on the windshield, quickly wipe it off with paint thinner. If it is dried on the windshield, use a razor blade to get it off.
Never sand or spray paint in an enclosed area. Park the vehicle outside or in a well ventilated areas.