How To Use Fiberglass Body Filler To Repair A Rust Hole In The Wheel Well Of Your Vehicle

If you own a car with a rust hole in the wheel well, then you need to take care of the problem as soon as possible. The rusted area will continue to spread, and an opening in your wheel well will also permit rust-causing agents, such as road salt and dirt, to penetrate the interior of the rocker panel. Fortunately, you can successfully repair a rust hole by using fiberglass resin. Here is a list of materials and tools needed to make the repair, as well as an easy-to-follow procedure:

Tools and materials needed

  • Can of auto body fiberglass filler

  • Tube of fiberglass hardener

  • Plastic putty knife

  • Roll of wax paper

  • Wire brush

  • Flat-bladed screwdriver

  • Angle grinder

  • Wire brush wheel

  • Bottle of rust inhibitor/remover

  • 1-inch paint brush

  • Garden hose with spray nozzle

  • Safety glasses

  • Work gloves

  • Plastic cutting board

  • Wallpaper seam roller (optional)

Step-by-step procedure

1. Practice safe working habits - While working, you must wear safety goggles to protect your eyes from flying fragments of rust and steel, and also be sure to wear gloves to guard your hands from nicks and cuts. In addition, be careful while using the rust treatment agent; it is acidic and can cause chemical burns to your skin and other tissues.

2. Remove the rust from the wheel well - Begin the process of removing rust from the wheel well by using a wire brush to scrape away obviously-loose pieces of rust; if necessary, chip the rust chunks away with a flat-bladed screwdriver. Once the loose pieces are removed, use an angle grinder with an attached wire brush wheel to scrape away the remainder of the rust. When using the grinder, try to blend in the edges of the repair site with the surrounding non-rusted metal.

After removing all visible signs of rust, rinse the site of the repair with a garden hose and spray nozzle to clean away the rusty residue. Allow the repair site to dry completely, and apply a coat of rust inhibitor/remover to the surface of the repair site with a paint brush. Once the rust inhibitor/remover has dried, you are ready to proceed with the remainder of the repair.

3. Prepare the fiberglass filler for placement - Use a plastic putty knife to scoop out a small amount of fiberglass filler and place it on a plastic cutting board. You can determine the amount of filler needed by estimating what it will take to cover the hole in the wheel well with a ½-inch layer of filler, while allowing an overlap at each edge of the hole of about 1 inch.

Once you have scooped out the needed amount of filler, squeeze a ⅛-inch wide line of fiberglass hardener across the top of the filler. Begin stirring the filler and hardener together with the putty knife until it is thoroughly mixed. Transfer the combined filler and hardener mixture to a sheet of wax paper, then flatten it with the putty knife to form a flat, ½-inch thick piece in the shape of the rust hole with an extra inch on each side. Be sure to work fast, as the filler will quickly solidify once the hardener is added.

4. Place the fiberglass material in position - After laying out the repair piece on the wax paper, carefully pick up the wax paper and push it into position over the hole. Using your fingers, shape the fiberglass material through the backside of the wax paper so that it blends with the surrounding metal and adheres firmly to the metal. If desired, use a wallpaper seam roller to flatten the material and add a finished look to the repair site.

Once you have placed the filler material, allow it to set for 5 minutes, then gently pull the wax paper to see if it will cleanly pull free from the fiberglass. If it doesn't, allow it to continue setting for another 5 minutes, then repeat pulling the paper. Once the paper separates from the fiberglass cleanly, pull the paper off and discard it. Perform a quick visual inspection of the fiberglass to be sure it is in position and looks as it should. Allow the fiberglass to harden overnight before attempting any finishing such as sanding or painting.

If you're uncomfortable doing this process yourself, contact a local auto body repair shop.