How to Repair a Rusted Undercarriage of a Car

When a car's undercarriage rusts, you need to repair it immediately. Rust leads to weakening of the car's structure and eventually holes in the floor of the car. This is a danger to passengers and drivers alike. Repairing rusted undercarriages takes time; usually an afternoon or more is required. If you have not attempted this repair before or similar body repairs, allow yourself extra time to finish the job.

Instructions

1

Remove the carpeting by pulling it up from the floor of the car. Use scissors or a knife to cut the carpet away if necessary. Or lift the car onto a hydraulic jack to gain access to the undercarriage area that requires repair.

2

Sand away rust spots with abrasive sandpaper on a block, or use a power drill and grinding disc for large areas of rust. Wipe down the undercarriage, after sanding, to remove all dust and sanding debris.

3

Clean the area with a solvent or automotive degreaser to remove dirt, grease and oil. Dry the area with a shop rag until all of the degreasing agent is removed.

4

Cut fiberglass strips to the proper length to cover the repair area. For best results, use several overlapping strips to cover the area to improve the strength of the repair.

5

Mix fiberglass resin and hardener compound in a container using the prescribed mixing ratio in the hardener instructions. Spread the fiberglass resin onto the strips with a plastic applicator then apply them to the undercarriage, covering the entire area with new fiberglass.

6

Allow the fiberglass to dry and harden overnight. This usually takes 12 to 24 hours. Sand the repair with 200-grit sandpaper until smooth. Paint the repair with automotive primer and a final top coat of automotive paint to seal the area.