How to Fix Rust Holes on a Car

It’s important to fix rust holes on your car. They can make the vehicle susceptible to more corrosion, it can spread, and it can cause you to fail a state inspection. Rust holes can even form from just a little bit of rust that’s not attended to. This guide and video reviews how to fix rust holes on a car by cutting out the rust and welding in a new piece of metal, and then filling in and painting the area. This guide is more for DIY work on an older vehicle looking to pass state inspection than for restoring a classic model.

How to Remove Rust Holes from Your Car

Mechanic showing how to fix rust holes on your car

Tools Needed to Fix Rust Holes

  • Safety glasses
  • Gloves
  • Mask
  • Metric sockets
  • Die Grinder
  • Cut off wheel
  • Vacuum
  • Metal cutters
  • Welding gloves,
  • Welding helmet
  • Welder
  • Welding magnet
  • Body filler
  • Body filler hardener
  • Piece of cardboard
  • Plastic spreader/Squeegee
  • Hammer
  • Acetone cleaner
  • Cloth rag
  • Plastic sheets
  • Painter’s tape
  • Welder, welding helmet, and welding apron
  • Wet towel
  • 36, 40, 80, 120, 220 grit sand paper and sanding block
  • Dual action sander
  • Sponge
  • Water
  • Non-abrasive scuff pad
  • Primer
  • Paint
  • Clear coat

How to fix rust holes on a car

  1. Remove Rubber or Plastic Parts Near the Area

    Remove any rubber or plastic parts like weatherstripping that are located near the area

  2. Disconnect the battery

    Disconnect the negative battery terminal

  3. Grind the Metal Down Before Cutting Out the Hole

    Grind the metal down first with an air grinder or an electric grinder before cutting. Cutting before grinding can chew up the grinder and damage it. You can try to grind it down by hand, but it will take a long time, so we strongly recommend an air grinder. Chip away the rust and bad metal with a hammer or screwdriver. Wear safety glasses and grind away the metal with a die grinder

  4. Cut Out the Hole with a Cutoff Wheel and then Vacuum the Area

    Mark the area you want to cut out with a marker, and then cut out the area with a cut off wheel. When using the cut off wheel, make sure the sparks that fly off don’t hit any areas that are flammable, like the carpet. Be careful when removing the old hole since the edges will be extremely sharp. Vacuum out the area to pick up loose or sharp scrap metal

  5. Cut Out a New Piece of Metal and Rough the Edges with a Grinder

    Trace the old piece of metal onto the new one with a marker. Cut the new piece of metal from a metal sheet with metal cutters. Put the new panel up to the hole and test how it looks, but be careful because the edges will be sharp. Trim down the new metal as needed.

    Use a die grinder to rough the edges of the new piece of metal. This will help the new metal stick better when welding. With the new metal piece grinded down, use a welding magnet to keep the metal in place for welding.

  6. Weld the New Piece of Metal on

    Before welding, make sure the battery is disconnected. When welding on the body, you do not want to have any of the modules spike in voltage. Wear the proper protective clothing like welding gloves and a welding helmet.

    Pick a part on the body to connect the welding ground that is far away enough from the area being welded so as to not melt it. Have a fire extinguisher nearby or know its location. It’s also a good idea to have a bucket of water or a bottle of water in the case of a fire.

    Start by welding the corners with a nice bead. Place a bead on each corner. Apply a tack weld every inch to two inches between each corner. This will prevent the metal from warping. A continuous bead will contract and warp the metal. This will also make it harder to work on. Apply a tack every two inches, and then apply a closer tack during a second run-through. This will keep the metal cooler and from warping

  7. Grind Down the Welding, Touch It Up as Needed, and Clean the Area

    Grind down the welding with a grinder, and then touch up the welding by welding any open spots.

    Tap the metal with a body hammer for any high spots. If you put body filler on and there are high spots, you wont be able to sand them down when it’s time to sand, so make sure these are lower on the new panel. Grind about an inch above where the panel was welded to apply about an inch of body filler.

    Clean the area with a rag and acetone or another kind of alcohol cleaner. With the panel scuffed up, the body filler will stick to the body better

  8. Apply Fiber Glass Body Filler to the Body

    Apply fiber glass body filler to a cardboard or another sturdy disposable surface to contain the filler. Do this filler first before doing a regular body filler for the skim coat. This will harden and be more resilient to outside elements or impact.

    Create a circular amount about 3 inches thick and then place hardener filler down the center. Don’t mix it in a circle to prevent air bubbles, just fold it over, and don’t mix it until you’re near the rust hole since it will harden quickly. This will cause it to change color.

    Apply the filler to the area. Press it in hard to remove any air bubbles. The smoother you spread it, the less you’ll have to sand later. Let it dry, and then sand it. Normally, it takes about 10 minutes before you can sand it. Then put a finish coat of filler on top.

  9. Sand the Body Filler

    Sand it down with a sanding block and sand paper and wear a dust mask. If working outside, a fan blowing behind you can push the debris away. Sand in crossing patterns and on angles. This will prevent waves from forming in the compound mixture/filler.
    Apply more fiber glass filler if needed and sand the area again with 80 grit paper or lower grit like 36 or 24. The coarser the sandpaper is, the better.

  10. Apply a Skim Coat of Body Filler on Top and Sand It

    Skim coat the new metal with body filler without spreading it too thick so you don’t have to sand more. Use 80 grit to start and possibly go to 100 or 120 grit. Sand in a crossing pattern.

    When there are no low spots, use a dual action sander to finish since it orbits and doesn’t spin, which will limit damage. Try to feather it in to the paint.

    Apply another skim coat to cover any more rough areas, and then sand it with finer sand paper. Use 220 grit if sanding with a dual action sander. If sanding by hand, start with 80 to 100 grit, and then for the final coat use finer paper, like 200 or 220 grit.

  11. Clean the Area of Dust to Prep for Paint

    Before prepping for priming, remove the dust from the area. Blow the dust off with a blow gun. If you don’t have a blow gun, a leaf blower and/or a fan will also work. Remove as much dust as possible. Then clean the area with acetone or alcohol cleaner and a cloth

  12. Protect Open Areas with Plastic or Newspaper and Apply Primer

    If there is no body line to mitigate the difference in paint, you can feather it in. Place a tape line as a marker to contain the area for where to blend, and plan to blend beneath this line. Place plastic sheets over any area you would like to prevent paint from possibly spreading, like the tire, interior/doors, or higher areas than the one you’re working in.

    We’re using rattle can paint and primer in this example and not professional paint and primer. Check the directions on the primer for the appropriate temperature to be working in. Soak the primer and paint cans in a bucket of warm water for 10 minutes before spraying and the paint, which will help them stick better. Wipe down the area one more time with acetone before in the case any dust got on the body. A tack cloth will also work.

    Wear a mask that works with paint and be in a well-ventilated area. Have a door open or a fan exhausting the fumes. We’re using a sealer primer, but there are filler primers where you can wet sand if you’re concerned with appearance.

    Fill in the areas that need more primer first. Spray the primer in a sweeping back and forth motion. Hold the can 8 to 10 inches away from the body. Then let it dry and inspect how it went.

  13. Sand the Primed Area and Apply More Primer as Needed

    Since we’re not using a filler primer, we did not wet sand. Lightly sand the area with a scuff pad and where the primer meets the old paint. This will help the new paint stick to the vehicle better. 400 grit dry sand paper can also help with this. Scraping gently enough without finger tips won’t create finger lines.

    You can also place a sponge on the back to reduce the pressure applied, and consider wet sanding for a smoother finish. For wet sanding, use 400 grit paper and water. If you bleed through to any of the metal underneath, you’ll want to reprime it.

    Once finished, wipe the area down with a rag. Apply more coats of primer if needed, then sand (or wet sand) again and get ready for paint.

  14. Spray Paint Over the Primer

    Wear a mask and be in well-ventilated area with right temperature for painting. Spray the paint in the same way as the primer, in sweeping motions. You can test how well the color matches by spraying on piece of cardboard first and comparing it to the color on the vehicle.

    Spray about 8 to 10 inches away from the body. Don’t spread it on too thick, because this can create runs of paint. You’re better doing more thin coats than a few thick ones. You may spray the paint a little higher than the primer, so and make sure you don’t have any thin spots.

  15. Apply Clear Coat

    Shake the clear coat for about a minute. Once mixed up, spray it in the same way you sprayed the paint. This layer will protect the paint. Spray it higher than the paint job for better blending.

Want More DIY Work and Tips? Learn How to Fix More than Rust Holes on Your Car

Learn how to fix more than rust holes on your car with our how-to videos. Our videos have step-by-step instructions from professional mechanics to help you with all kinds of repairs and diagnosis on tons of makes and models.

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How to Fix Rust Holes on a Car - Expert Advice - 1A Auto
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How to Fix Rust Holes on a Car - Expert Advice - 1A Auto
Learn how to fix rust holes on a car or truck by cutting it out, welding on a new piece, covering it with body filler, and painting it with these steps from our expert mechanics
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1A Auto
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