Over time, rust can eat through the metallic surface of any vehicle. Eventually, it will require rust repair to remove the rust. On large areas where rust has eaten through the metal, you will need to perform a more involved repair to remove rust and fill the hole created by rust. Here are the steps required to use Bondo, a repair putty, for rust repair.
Step 1 - Locate Major Rust Deterioration
Some places on your vehicle's surface that are rusted completely through the surface will be easy to spot. Other areas may be deteriorated enough that the vehicle's metal surface is rotted but still has not created a hole, or opening in the surface. Although you will need to fill in both of these types of rust damage, the treatment needed to repair them will likely be different. You will need to carefully examine all surfaces on your vehicle to identify areas that require rust repair.
Step 2 - Clean Off Rust, Dirt, Paint, and Debris
You will need a strong, bare, and rust-free metal surface for your resin and Bondo to adhere to. To prepare your vehicle's surface in areas where it is completely rusted through, use a disc sander or grinder to remove all rust and debris from both the inner and outer surfaces. For surfaces that are rotted by rust but have not rusted completely through the surface, use a putty knife or chisel and remove chips and loose metal that has rusted. Then, use a disc sander or grinder to remove all rust, debris, and paint on the area you'll be applying epoxy or Bondo to. You will likely create holes or openings in the metal when you do this.
Step 3 - Apply Fiberglass and Epoxy
After mixing your epoxy with its hardener, apply it to the inside surface where you've removed rust and debris. Apply enough of the epoxy to a piece of fiberglass fabric that the fabric is soaked, then press the fabric into place over the hole, so that it closes the hole and creates a new surface. Allow the resin to harden. There is no need to apply the fiberglass or epoxy to surface areas that are pitted but have not rotted completely through the metal.
Step 4 - Apply Bondo
When your epoxy has hardened, use your grinder, or sander, to smooth off any rough spots on the surface you'll be applying Bondo to. On your mixing pallet, mix the Bondo and hardener. Using your putty knife and spreader, apply Bondo to the surface that has been created by your fiberglass and epoxy. When finished you should have a relatively even surface with all surface holes and pits filled. Allow the Bondo to harden.
Step 5 - Smooth and Paint Your Surface
Use your rasp and sanding block to smooth your new surface. With a clean rag, wipe off any dust or debris left from sanding. Spray on your paint primer. When it is dry, use a fine sandpaper to smooth the primer, wipe off primer dust, and spray on your touch-up paint.