How To Perform Rust Repair On Your Project Car (Without Welding)

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Home mechanics and car rebuilders far and wide often find themselves face to face with issues of rust — you can spend time employing all sorts of ways to protect your car from rust, but sometimes it still happens. The oxidation of steel is completely natural, and it happens often on older vehicles without discrimination of place or model — rust may also be something to worry about if you're a new Cybertruck owner. The trouble begins when paint starts to chip, wear, or bubble. Paint acts as a natural barrier between the bare sheet metal of a vehicle's body and the destructive force of the elements that cars spend their time weathering. When paint chips or otherwise breaks, it allows the interior metal face of the vehicle to become exposed to moisture. Naturally, cars that have been in collisions often suffer from rust damage since the crumpling of body parts leads to a breakage in the flat layer of paint that runs across the surface of the vehicle.

Project cars tend to be those that have seen better days for one reason or another. They may be old classics that have sat idle for many years, or new and athletic autos sold as a result of damage or other issues. In addition to rebuilding an engine or updating the transmission, handling routine rust repair is a skill that car enthusiasts should learn. Fortunately, many minor and moderate rust issues can be handled without the need to delve into welding. The process is actually quite simple — it's just a bit time-consuming.

There are quite a few steps involved in rust repair, and many can be performed with little downtime between them. As a result, it's a good idea to gather all of the supplies you'll need before starting the project. With most of the day set aside for the job, you'll be able to finish almost the entire project in one session.

Rust repair involves successive runs of sanding and filling, followed by repainting and the application of a clearcoat. A Bondo fiberglass body filler — something every home mechanic will want to have around anyway — will do most of the heavy lifting here, but you'll also want finish filler, rust reformer, and rubberized spray primer, as well as a variety of dry and wet sandpaper grits. Dry sandpaper will range from 80 to 600 grit, while your wet sandpaper will run up to 5000 grit. You'll also need masking tape, a small hammer — ideally a ball peen hammer with both flat and round striking faces — spray paint that matches your car's existing color, and a clearcoat. Scrapers, a sponge, and perhaps even a can of compressed air will also make the job more manageable, and a Bondo glazing putty is necessary to complete the perfect repair. Lastly, it's a good idea to either tackle rust repair outside on a sunny day or bring a fan into the workshop to create good ventilation for both the work surface and your health if an outdoor environment can't be guaranteed. No matter where you'll be doing your rust repair, wear a mask to prevent the inhalation of potentially harmful dust.

Next, you'll want to dent the area you've just sanded. Get your hammer out and begin to tap on the bare metal until you've created a small depression across the entire surface. Beating against a flathead screwdriver or any other similar tool can also create the small dents you'll be after at this stage. In later steps, you'll begin filling in this area to return the vehicle to its former glory. But your filler will need a space and without hammering in the sheet metal it will have to sit on top of the surface rather than run flush with the surrounding curvature of the car's chassis. A ball peen hammer is a versatile solution during this step. The rounded striking face on the back end of the hammer allows you to smash parts of the sheet metal in with a precise strike, while the flat face offers a wider contact surface for more general striking.

If you aren't able to find this kind of hammer, a light-duty claw hammer can work as well. A lighter hammer gives you greater control — it may not be ideal for driving large nails, but it's the perfect tool for this kind of precision divot creation.

The inner surfaces of your vehicle won't get the same paint treatment that the outer face receives. However, you still need to treat any rusted surfaces you repair, regardless of where they are found on the car. A rust reformer is a type of undercoat that will ensure rust can't make a comeback where it's applied, even if you missed a spot or two. It bonds to any rust left over and creates a sealed and paintable surface. Spray a coat of this on any inner area you sanded to add an additional layer of security.

After this coat has dried, spray your rubberized primer in a thick coat along the area. It's important to use a rubberized variant because this will add immense durability to the inside portion of your vehicle. This kind of primer will resist chipping and flaking and therefore create a tough, cohesive layer to resist future rust issues with ease. As is the case with sanding, some areas you may be repairing can be difficult to reach. Take your time and make sure that you've coated the entire space thoroughly, and don't be shy with the primer.

Bend your putty knife and simply pull off the hardened filler before moving on to sanding the filled surface of the vehicle. Get your sanding gear back out and begin to run along the lines of the car's curvature. It's important to keep in mind that car bodies have a variety of lines, edges, and angles etched into their figure. You don't want to just sand blindly across the surface. Instead, take note of where any edges or lines may be and ensure that you're sanding flat against their arcs. This will give you a rough outline of the edges that existed before rust damage began to eat away at the vehicle.

It's important to take as much time as you need when sanding these lines accurately. However, the overall sanding job doesn't have to be perfect at this stage because you'll be applying more filler once you've flattened out this first coat. Once you've finished sanding, get your Bondo professional gold filler (or any other kind of finish filler) and repeat the steps above. Mix the finish filler and hardener together and then apply a thin first coat to the car before building up the repair surface with additional finish filler. Allow this filler layer to cure for 20 minutes before moving on to your next sanding task.

Before any painting can be done, you'll need to apply a primer. However, it's important to use a filler primer rather than just any undercoat. Bondo filler primer is made specifically for this purpose and includes a little finalizing filler to smooth out any leftover micro-abrasions or imperfections in the repaired surface. This gives you just a bit of extra surface prep to continue smoothing out the repaired surface before applying your color.

A tip that YouTuber ChrisFix offers up at this stage can be immensely helpful to anyone not particularly confident in their painting skills: Rather than taping off the area that will be primed and painted, gently fold over a few sheets of paper and tape them around the surface to create a rounded edge instead of a harsh tape line. This will make blending your repair into the surrounding car body a bit easier when you're sanding down the primer and later painting. Once you have the surface ready, including cleaning it once again, apply three coats of filler primer while letting each coat dry for the time specified on your can. Once the primer is dry, sand the surface with 600-grit sandpaper, making sure to work up into the original paint job by an inch or two. Then, apply three coats of your match color while allowing each to dry to a matte finish before starting again.