Bondo: Repairing Rust Damage

Bondo: Repairing Rust Damage

Rust-outs on a vehicle are unsightly and can spread quickly if they’re not addressed.

Rust-outs on a vehicle are unsightly and can spread quickly if they’re not addressed.

3M, which makes Bondo body filler, offers these simple steps for repairing rust-outs and keeping your vehicle in prime condition:

  1. Start by washing the spot you’re going to repair and then wipe it down with a VOC-compliant adhesive remover to get rid of any wax or other buildup. If using a drill, use 36-grit disc or 80-grit 3M sandpaper. Remove all paint and rust from surface, then smooth out all grinding marks with 80-grit sandpaper followed by a VOC-compliant adhesive remover to remove all sanding dust.
  2. Next, tap the rusted area with a body hammer to create an indented area so that when Bondo Glass Filler is applied, your repair will be even with the surrounding area. If you find yourself with a larger rust-out than you anticipated, utilize a Bondo Self-Adhesive Body Patch to bridge the larger area. Cut it to fit inside the dented area with household scissors.
  3. Now it’s time to mix your Bondo Glass Filler, which will provide additional strength to the repair, on a non-absorbent surface. Place a three-inch puddle of filler on the surface and add a two-and-a-half- to three-inch strip of hardener across the puddle. Firmly fold the hardener into the filler until it’s all the same color – make sure not to stir in a small circular motion, as that adds air that will show up as pinholes in your repair.
  4. Once your filler is properly mixed, start with a small, thin layer followed by several back-to-back layers. Apply enough filler to the rust-out so it’s slightly higher than the surrounding area. Let the filler dry completely.
  5. Shape and sand the repair with 40-grit sandpaper and then even it out using 80-grit sandpaper, blow off, mix and apply a coat of Bondo Body Filler using the same mixing directions from step three and four for a smoother finish. Allow the Bondo Filler to cure and start sanding with 80-grit sandpaper to shade and level the repair. Then apply additional filler if needed to level the repair. If the area is smooth and level, finish sanding with 180-grit sandpaper and blow off the repair area to inspect for quality.
  6. If there are pinholes in the repair after sanding, apply a very thin coat of Bondo Glazing and Spot Putty to pinholes. Allow to cure, and finish sanding with 320-grit sandpaper. Then you’re ready to prime and paint.
  7. Once the area is painted, apply 3M Rust Preventer Spray to the back side of the rust-out area to extend the life of the repair. Follow the directions on the container for safe and proper application.

“The Bondo brand provides products that any auto DIYers can rely on to get the job done right,” said Matt Callahan, global marketing manager for 3M Auto. “By utilizing Bondo-brand fillers and following these simple steps, anyone can simply and economically repair unsightly and damaging rust-outs on a vehicle.”

The 3M product line and Bondo products can be found wherever automotive products are sold. For more information, visit or

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