We've patched quite a few vehicle dents in our day. We used to do it the same way we tape drywall, by applying 5 lbs. of body filler and then sanding off 4.9 lbs. Then we went to “boot camp” at 3M and learned there's an easier way (as in, the correct way) to do dent repairs.
We asked 3M expert Jenn Cook to walk you through the same dent repair process. Once the dent is patched, you just spray on a primer coat and matching paint from the dealer or an auto parts store. The repair won't look like a professional job, but at least it won't stand out like a sore thumb. Here's the process.
Stop at any auto parts store and buy a 24-grit sanding wheel and sheets of 80-, 180- and 320-grit sandpaper. Also buy a bottle of wax remover, a tack cloth, a mixing board, several plastic spreaders and a tube of finishing glaze.
Finally, you'll need body filler. Professional-grade filler is creamier and easier to spread and sand than bargain-priced products, so it's worth the extra cost. One choice is Bondo Professional Gold Filler.
Start by removing the paint inside and around the dent with 24-grit paper. Switch to 80-grit sandpaper and hand-sand the entire dent. Use the same sandpaper to rough up and feather the paint around the edges of the dent. Clean the entire area with wax remover and a clean rag. Then wipe with a tack cloth.
Don't mix body filler on a scrap piece of cardboard. Instead, use a mixing board or an old, clean cookie sheet you're willing to toss.
Scoop filler onto the mixing board and apply the hardener according to the directions. Then mix it using a spread-and-fold motion. The spreading and folding technique fully mixes the hardener into the filler and prevents air bubbles from forming. Never stir the mixture.
Spread the filler to form a “tight” coat. That will burp air out of the scratches and wet the bare metal. Then apply a fill coat.
Sand the filler to match the contours of the car body using 80- and 180-grit sandpaper. Then feather the edges of the filler right up to the painted edge.
Next, apply finishing glaze to the entire patch and then sand with 180- grit and then 320-grit sandpaper. Spray the patch with primer, and then paint it.