How to Do Auto Body Repair Work
This tutorial explains how to do auto body repair work on sheet metal panels, not the plastic/fiberglass composite skins which have rolled off the assembly lines for years. This article covers the use of auto body filler as a repair medium. Although true that welding or riveting a steel patch into place makes a stronger repair, most vehicle owners have neither the equipment nor the experience. While this article specifically addresses rust repair, many of these steps also apply to dent repair.
1. Remove the damaged body panel for repair, when you can. Lay it down on a sand bag to hammer out any dents from the inside out. Use a plastic hammer or rubber mallet to start and finish with a wide-faced auto body hammer for the smoothest appearance. Use a block of wood as a solid backer, to avoid stretching the metal.
2. Use a wire wheel or a sanding wheel mounted in a drill to remove spot or surface rust. Once you have removed the rust down to bare metal (inside and out) skip forward to step 6. If the rust has eaten a hole through the panel. Use a pair of sheet metal snips to cut out all the jagged sections of damaged metal.
3. Use a pair of channel-lock pliers to recess the edges surrounding the hole left from the damaged area removed. Bend the steel inwards then back, creating an 1/8" recess. This allows for enough Bondo to hold tight to the screen for a long-lasting durable repair.
4. Cut a square section of 1/4" galvanized screen mesh just larger than the hole and coat it with rust preventative primer. The following describe the remainder of this repair with the panel installed:
Tie nylon fishing line to the center of the galvanized screen. Roll it up and insert it into the hole where it will open up to span the inside of the void. Hammer a stake into the ground next to the vehicle and tie the fishing line to it, pulling the screen tight inside of the hole. If you perform this repair indoors, find a suitable stationary object to tie the line to. As an alternative, cut the screen to fit the recess itself and pop rivet it into place.
Bondo 1st coat
5. Mix just enough Bondo (resin and hardener) to work with, as it dries quickly! Using the trowel from the kit, gently apply the filler to the screened section and recess, allowing it to cure before proceeding. The softened body filler curls around the screen and anchors it to the sheet metal. When dealing with small dents or surface rust, drill a series of 1/16" holes to simulate the screen and provide anchorage.
Bondo finish coat
6. Cut the fishing line and apply a filler coat after the initial coat has cured. Do not apply more than necessary, since you must remove cured excess by sanding it flush. No sense making more work for yourself. Apply a thin skim coat to fill in any imperfections, after the filler coat cures and you have sanded the Bondo flush with the surface of the sheet metal.
Mask, prime & paint
7. After sanding the skim coat to perfection, remove all dust with a clean rag lightly dampened with rubbing alcohol. Mask off the area and apply primer. Onto this, apply at least two coats of finish paint. Apply at least one coat of clear-coat sealer to protect the paint.
* If the repaired area is subject to being exposed to moisture from behind (door panel, fender or quarter panel), be sure to prime/seal the unseen surface of the Bondo, using either automotive primer or rubberized undercoating.
* Apply Bondo in several thin layers, allowing each to cure thoroughly before sanding.
* Clean up with Acetone. Acetone is a highly flammable solvent, exercise caution.
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