Rust is a common affliction to most older cars. It occurs whenever oxygen from the air comes into contact with metal that contains iron. A car's paint and top coat protect the metal from oxidation, but as the environment damages or wears away this protection, rust is inevitable. Because of their position on the vehicle, car doors are a common site for rust. Thankfully, you can remove rust and prevent it from spreading with just a few easy steps.
Remove the Rust
Remove as much of the rust as possible by hand. Start with coarse sandpaper or a metal file in cases of more advanced rust. Gradually progress to a finer sandpaper or an abrasive cloth until the rust is gone and the area is smooth. An abrasive cloth is also best when rust occurs in a seam or narrow space that you can't reach with sandpaper.
Treat the Area
If there is any remaining rust, apply an oxide conversion fluid. This chemical compound will neutralise any remaining rust and provide a smooth surface for repainting. If you're sanding or filing created any gaps or pits in the metal of the door, use a body filler putty to fill in the holes. Allow the putty to dry according to manufacturer specifications and then sand the surface smooth.
Clean the Area
Once the oxide conversion fluid or body filler putty has dried, clean the entire area with a damp, soft cotton or microfiber cloth. Make sure that there are no stray rust flakes or dust from the sanding process.
Paint the sanded area with a spray gun or aerosol product. Paint several thin layers, allowing each layer to dry between coats. Be sure to check the directions on the paint you choose, which will specify drying time and also what temperature range is required for the paint to cure properly.
After applying several coats of paint add a top coat. Use this layer to give the door surface a new protective layer, and also to blend the repainted section into the rest of the door. Apply a coat of wax to protect the area from moisture.