Posted April 19, 2021 by Jefferson Bryant Know How

Rust Repair 101 – How To Fix A Rust Hole

Rust repair and body work comes along with just about every old car project. For the novice builder, these tasks can mean a costly trip to the body shop or lots of frustration in the driveway. It doesn’t have to be this way though. Proper techniques and tools for rust repair will help make any project easier to accomplish. Practice is an important step in learning the ropes of body work, but who wants to spend hours practicing on something that doesn’t further the project? Locating a good practice panel on your ride that is less visible is a great place to start.

Small rust holes offer beginners a great way to practice rust repair. While replacing large sections can be relatively easy, the smaller rust holes that do not warrant a full panel replacement are small enough that the average builder can tackle them and be back inside in time for dinner. Let’s take a look at how to fix rust holes on a car the right way.

Rust Repair Tools

There are a few tools that take a lot of the pain out of this type of procedure. You need a cut-off wheel to remove the offending material in a clean manner. Usually there is something behind the rusted area, so you need to be careful not to cut through it. The cut-off wheel gives you the control. You can also use a vibrating cutting tool, like side-side reciprocating tool.

A good welder is also paramount for a good weld. You need to be able to weld thin sheet metal, and that means thin wire (.024” is best for thin gauge sheet), and low heat.

Before You Begin

Technique is really the biggest key to a quality job. When welding a panel, especially a long panel like a quarter, using the stitch method will reduce warpage. Welding creates a lot of heat and the sheet metal will twist and band away from the heat. The stitch method involves first making a few spot welds to hold the panel in place, then adding short 1-inch stitch welds, skipping about 4-5 inches, then another and so on. This reduces the amount of heat each area is exposed to. Using an air blow gun to cool the area reduces the heat effect even more. Another good idea when replacing any type of sheet metal is using weld-through primer. This high-zinc paint helps protect the backside of the sheet metal from rusting, a very important step in the restoration process, this is something most people forget, and they end up with rust bubble just a few years down the road.

The trunk lid from a 1971 Buick GS had some rust bubbles under the trunk badge. The car was getting a repaint, so these had to be tackled immediately.

Getting To Work

To demonstrate this process, we cut out and repaired some rust bubbles in the trunk lid of a 1971 Buick GS convertible. This is the kind of rust you find under those little bubbles in the paint. We started by stripping the trunk of paint.

These are the holes. Now a few of these are holes for the badge, the big ones are just rust.

A patch panel was made from 14-gauge steel and coated with weld-thru primer to keep it from rusting.

Next, we cut out the offending area with a cut-off wheel. Notice the rust behind the section. We treated this with rust killer and then some undercoating. — Next, we cut out the offending area with a cut-off wheel. Notice the rust behind the section. We treated this with rust converter and then some undercoating.

The scale was knocked off with a wire brush and then treated with rust killer. — The scale was knocked off with a wire brush and then treated with rust converter.

Once the rust killer had cured, it was sprayed with undercoating to seal it. — Once the rust converter had cured, it was sprayed with undercoating to seal it.

The panel was fit and then held in place with magnets.

Using the stitch-weld method, the panel was welded into place.

The last step before body work is grinding down the welds. A flat grinder works, but a flap-wheel disc cuts faster and does not heat up the metal nearly as much.

Take your time and practice before you actually weld on your car. Rust repair is not that hard, but it is really easy to make a bigger problem if you get ahead of yourself and bite off more than your skills can handle. The key here is patience and when in doubt, seek professional help.

Check out all the tools & equipment available on NAPAonline or trust one of our 17,000 NAPA Auto Care locations for routine maintenance and repairs. For more information on rust repair, chat with a knowledgeable expert at your local NAPA Auto Parts store.

Jefferson Bryant View All

A life-long gearhead, Jefferson Bryant spends more time in the shop than anywhere else. His career began in the car audio industry as a shop manager, eventually working his way into a position at Rockford Fosgate as a product designer. In 2003, he began writing tech articles for magazines, and has been working as an automotive journalist ever since. His work has been featured in Car Craft, Hot Rod, Rod & Custom, Truckin’, Mopar Muscle, and many more. Jefferson has also written 4 books and produced countless videos. Jefferson operates Red Dirt Rodz, his personal garage studio, where all of his magazine articles and tech videos are produced.