The most annoying thing about owning an older BMW is rust. You might think that your car is rust free, but the truth is, it has rust.
- Do not use rust converter as an easy way out
- Clean the area to the bare metal with a media blaster. You can also use a metal grinder mounted on a drill
- Clean the area again. Get a commercial grade rust stripper and follow the instructions. Don't be afraid to use a wire brush on the affected area to speed up the process
- Repeat the process until the metal rust and particle free
- If the rust ate through metal, you may be able to save it with Bondo. We recommend a metal patch if you want to do the job once
- Sand down with 160-300 grit sandpaper, then follow with 600-800 grit to smooth everything out
- Apply sealable primer. Quality primer and proper preparation always beat a sloppy application of rust converter
- Sand the primer down with a 1000 grit paper
- Put down another coat of primer. You can start the paint process (or undercoating) once the primer cures.
To repair small holes in the metal, you will need to apply two to three layers of Bondo. Put a small metal plate and work the Bondo between the plate and the metal you are plugging. That will serve as additional bounding surface and give greater structural integrity to your repair.