Dents can be repaired in multiple ways, but the only sure way to repair any dent, no matter the depth or size, is to use a slide hammer. A slide hammer is also called a dent puller and is used by every bodyworks garage to remove dents. The slide hammer can completely repair a dent when used in conjunction with a few other materials, including body filler and primer.
Drill multiple holes in the dent in various places. Drill one hole in the centre and more holes a few inches apart, scattered throughout the dent.
Place the tip of the slide hammer in one of the holes. The tip of the slide hammer is threaded and works like a screw. Turn the hammer until it is screwed into the hole.
Hold the slide hammer with two hands, placing one hand on the sliding handle and the other at the end on the solid handle. Slide the weighted handled of the hammer down toward the car and quickly pull it back toward your body. Do this several times until the sheet metal inside the dent is pulled close to surface level of the car.
Unscrew the slide hammer and place it in a different hole and repeat steps 2 and 3. Alternate the holes so that the sheet metal is pulled out as evenly as possible.
Grind the sheet metal in and around the repaired area to remove all paint and primer. Get the area down to the bare metal. The holes drilled into the sheet metal are jagged and need to be grinded flat.
Cover the bare metal with auto body filler to smooth any wrinkles left in the metal. Allow the filler to dry for an hour.
Sand the filler using 80-grit sandpaper. Use a block sander or a dual-action sander to speed the process. Sand until the area is flat and smooth. Go over the area again using 180-grit sandpaper to smooth the deep scratches made by the 80-grit sandpaper.
Spray a coat of primer over all areas of body filler and bare metal. This protects the bare metal from rusting and seals the body filler from moisture. Now the area can be painted or taken to a paint shop.
Dents cannot be completely repaired using only a slide hammer. A drill and body filler must be used to help smooth a dent completely.
Never sand body filler without wearing a dust mask or respirator since the dust is toxic and can harm your lungs.