How to Spot and Replace Body Filler

Spotting and replacing poorly bonded body filler is an important step in restoring a car to showroom condition. Telltale rust spots or chipping paint are often signs of an unsuccessful repair. This is most likely where someone tried to repair dings and corroded metal without properly sanding, cleaning and priming the damaged metal before applying bonding material. Here's the way to correct bad body filler repairs.

Difficulty: Moderately Challenging

Instructions

1. Check the car body for rust spots or areas where paint is chipping or flaking off. Pay particular attention to wheel wells and the bottom panels around the perimeter of the car. These are areas where you'll often find patched body damage, corrosion and rust.

2. Probe any suspicious area with a knife blade or screwdriver. Bonding compounds are softer than metal and a blade will penetrate these areas, revealing the patch.

3. Grind down any bonded area you find with a power sander to remove all paint and surface rust.

4. Remove the bonding material. Use a torch to soften the bonding compound or chisel it away, depending on its location. Once you remove the compound, clean the entire surface around the damaged area down to bare metal.

5. Replace the patch. One way to do this is to form and shape a new piece of sheet metal and weld it into place, then grind it smooth and prep it for primer and paint.

6. Repair smaller areas with newer resin based bonding material by thoroughly sanding the bare metal you want the patch to adhere to using coarse sand paper. Get the area completely clean and dry, but don't sand it smooth. Leave it roughed up and apply bonding primer so the compound will bond properly. Be sure the surface of the surrounding area is completely dry and free of any condensation so you don't trap moisture in the patch or it will rust again.