How to Fix a Dent in a Car - Car Craft Magazine

How To Fix A Dent In A Car Our Project Car

Usually, progress up the car-building ladder is driven by necessity. It starts by just keeping that old beater on the road-learning to handle the simple maintenance and repairs that otherwise would have that old iron squeezing the wallet harder than a new car payment. Next comes tuning and tweaking, and hey, you're getting pretty good at this. With time we get into more ambitious projects, bolting together that killer mill or chassis. Finally, we become invincible. Every trashed-out hulk is seen as potential street machine fodder. That cast-away Nova in line at the crusher can be next year's show stopper. At this stage of the game, you're limited only by your imagination and skill...and, oh, yeah, those ever-scarce greenbacks.

Little in the car builder's arsenal can advance a project's possibilities more than some know-how in panel and paint work. The flip side is that metal mastery is hard earned. Look, learn, listen, and read all you can-but finally you must do. Years ago, the tools of the trade required a serious investment and the materials were awkward to work with, but today, jumping into the fray with some of the basics will pay off immediately. Once the craft is mastered, you'll never look at a derelict street machine the same way.

Enough to send even the most faithful spouse to divorce court, we actually fired up this four-speed 'Cuda from its resting place at the local wrecker's and drove it home. The mangled metal in the quarter is cleverly camouflaged by a random pattern of surface rust and age-old primer.
Enough to send even the most faithful spouse to divorce court, we actually fired up this f
Flexing an aluminum tube over the contour of the rear quarter showed the major dent over the wheelhouse to be nearly 2 inches deep, but we decided to repair the quarter rather than replace it.
Flexing an aluminum tube over the contour of the rear quarter showed the major dent over t
The first step was stripping the area to the bare metal. An angle grinder with a 36-grit disc made short work of the job. We kept the grinder moving to avoid overheating and further distortion of the metal. Use caution at the edges and creases-these grinders eat metal.
The first step was stripping the area to the bare metal. An angle grinder with a 36-grit d

The area was then buffed with a 3M Clean and Strip fiber disc to further scour the metal surface of paint and rust, again taking care not to burn the metal.
The area was then buffed with a 3M Clean and Strip fiber disc to further scour the metal s
Our unprotected quarter showed some deep surface rust and resultant pitting. Although nearly all traces of rust were stripped off, the surface was treated with an acid-based rust converter to deep-clean the pores. The rust converter was allowed to set up overnight, after which the surface was thoroughly sanded with 80-grit paper and a D/A sander. Paint, primer, or plastic filler will not adhere well if the treated surface is not re-sanded.
Our unprotected quarter showed some deep surface rust and resultant pitting. Although near
Beginning bodyman's basics: You can go a long way with a hammer and dolly kit such as this low-buck set from Harbor Freight Tools (about $20). The challenge is getting a feel for working metal, and there's no shortcut for practice. On the left is the dreaded slide hammer dent puller, used only as a last resort.
Beginning bodyman's basics: You can go a long way with a hammer and dolly kit such as this

Had our dent been in an easily accessible part of the trunk, it would have been a simple hammer-and-dolly job. With more than two-thirds of the dent behind the wheelhouse, we had to get creative. The cop-out would have been to dust off the slide hammer and start drilling holes. Starting at the deepest point, we levered the dent outward with a prybar while simultaneously hammering the adjacent metal surrounding the prypoint. This lets the area take a set at the pried-out level.
Had our dent been in an easily accessible part of the trunk, it would have been a simple h
Various bars up to 3 feet in length were used to work out the dent, as well as combinations of bars with dollies as shown here, all the while confining most hammer work to the outside of the quarter. Had the dent been easily accessible, the dolly would have been used to back-up the dented area from the outside while the dent was hammered out from inside. Tricky jobs like this mean coming up with innovative solutions and tools for getting the job done. Experience goes a long way here.
Various bars up to 3 feet in length were used to work out the dent, as well as combination
As the area got closer to its final shape, a quick hand sanding with 40-grit in a block revealed high and low spots as light and dark areas respectively, helping to guide our work. Again, you can use a long, straight tube for checking the overall contour. For the average production bodywork job, the lid on the plastic filler would have already been popped by this stage.
As the area got closer to its final shape, a quick hand sanding with 40-grit in a block re

Sometimes, when the metal has been substantially stretched, a bulge will result that will be impossible to work out. Frequently, an area like this will "oil-can" or just pop in or out. The only alternative is to shrink the area. This can be accomplished with a special shrinking hammer or, more commonly, with a torch. First mark the area that needs shrinking. To shrink it, heat an area about the size of a dime to a cherry red color (don't melt the steel), and then quickly quench the spot with a soaking wet rag. We had to repeat the process in more than fifteen spots to properly tighten up the body panel. After shrinking, the area will always require more hammer and dolly work.
Sometimes, when the metal has been substantially stretched, a bulge will result that will
Roughing out and heavily working the surface will leave the bumpy (although hopefully level) surface shown here. Smoothing (or, to use the correct terminology, planishing) the surface is done with a light flat-faced planishing hammer. Backing the area with a flat-faced dolly that approximates the panel's contour, the bumpy metal is hit with rapid, repeated, light hammer strikes, moving the hammer and dolly steadily around the work area.
Roughing out and heavily working the surface will leave the bumpy (although hopefully leve
We regularly checked the work area by gliding our hand quickly across the area to "read the dent." You will learn to distinguish between surface irregularities and an unlevel contour.
We regularly checked the work area by gliding our hand quickly across the area to "read th

It is possible to finish the repair area to a point where zero body filler is used, but the steps shown up to this point demonstrate a repair using far less body filler than you'll see in most production shops. We ripped a small hole in the panel but filled it (arrow) with lead body solder.
It is possible to finish the repair area to a point where zero body filler is used, but th
Today's lightweight plastic fillers are easy to use, flexible, and have excellent adhesion. The key to getting them smooth is to keep the material uncontaminated. Always mix on a perfectly clean surface, and use a clean plastic spreader with a good smooth edge. Mixing on top of a previously mixed batch, reusing the same stirring stick, or having dry residue on the spreader will invariably drop lumps of dried filler into the mix, which will plow in the filler while applying. Never use the same stick to scoop unmixed filler and stir in the hardener.
Today's lightweight plastic fillers are easy to use, flexible, and have excellent adhesion
We applied the filler in long, even, overlapping strokes. Don't be tempted to overwork the filler, as once it begins to gel, disturbing it will leave a cratered surface full of voids and air pockets. If filling to a character line, as in this case, break up the application by working to only one side of the line at a time.
We applied the filler in long, even, overlapping strokes. Don't be tempted to overwork the

To quickly cut back the filler, we worked it with a Surform file before it fully hardened. The rounded profile files are superior to the flat versions. The proper technique is to run the file at a 30- to 45-degree angle rather than straight across. Ideally, the surface will be close to level at the same time that the surface has uniform file marks and the edges are broken or feathered all the way around. If the surface is level but there are low spots that haven't been hit with the file, another application of filler will be needed.
To quickly cut back the filler, we worked it with a Surform file before it fully hardened.
The long sanding board is the key tool for a wave-free surface. Follow up the filing by sanding with 36- or 40-grit sheets in the long board. The coarse paper will cut and level, while a smoother paper will float, leaving dips and humps. Work the board at a slight diagonal and criss-cross the area by changing directions. When the filler is level and uniformly sanded, switch to 80-grit to smooth the heavy sanding marks.
The long sanding board is the key tool for a wave-free surface. Follow up the filing by sa
High spots will sometimes appear while sanding, especially if the metal work was done to keep filler thickness to a minimum. These spots can be tapped in with repeated light strikes over the exposed metal using the pointed end of the body hammer. The surface thickness of the filler here is little more than that of a heavy primer coat.
High spots will sometimes appear while sanding, especially if the metal work was done to k

Once the area above the character line was filled, we repeated the process below. When finished, the area was blown and tacked off, and then shot with primer (we used PPG Epoxy).
Once the area above the character line was filled, we repeated the process below. When fin
Plastic filler will always leave some pinholes and surface irregularities. To provide a surface that's uniform and has a fine grain, the filler is glazed. In the old days, glazing putty (basically the same as the spot putty) was nothing more than primer solids in a paste applied with a spreader. Regular glazing putty is tricky to apply smoothly over large areas, and because drying is by the evaporation of solvents, it tends to shrink and require long drying times if applied too thick. Modern, two-component polyester glazes are watered-down plastic fillers with fine grains. These go on smooth, dry by a catalyst, and sand easily-same rules as when working with the filler, only here a smooth application is even more critical.
Plastic filler will always leave some pinholes and surface irregularities. To provide a su
With the primer coat lightly sanded, blown, and tacked, the glaze is applied. Keep the glaze layer super thin, pressing it in firmly with long strokes. The glaze here was extended well beyond the filled area to glaze the rust scarring and grinder marks.
With the primer coat lightly sanded, blown, and tacked, the glaze is applied. Keep the gla

To be able to gauge the sanding process, the glaze is fogged with a light layer of contrasting primer (arrow). This is the guide coat. A shorter 6-inch sanding board with 120-grit paper is used on the glaze. Sand evenly until all the edges are feathered and the guide coat disappears. The glaze will be very thin and even transparent in places when fully sanded.
To be able to gauge the sanding process, the glaze is fogged with a light layer of contras
We finished with a coat of primer surfacer.
With the surfacer cured and sanded, this job is done. Now it's time to work on those untold dozens of other dents.
With the surfacer cured and sanded, this job is done. Now it's time to work on those untol