How to Replace Rusted Out Metal On A Car

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When dealing with rust on a car it is really just like you have always heard, that it works like a cancer and keeps eating away the metal unless you get rid of it. You can't just mask over it but have to remove it completely and replace the section with new sheet metal. This article is aimed at generally taking you through the steps of removing the old rusted metal and replacing with new 22 gauge sheet metal, which is a typical gage for general body repair for smaller panels and sections.

Things You'll Need

  • Grinding tool for cutting and grinding
  • 22 gage sheet metal (Sold in Hardware stores in various size sheets)
  • Sheet metal snippers
  • Sheet metal screws
  • Screwdrivers
  • Plyers and vice grips
  • Metal filler, epoxy or JB Weld
  • Bondo Body Filler
  • Spot putty glazing compound
  • Automotive high build primer
  • Rust treatment spray
  • Body hammers and dollies
  • MIG Welder and proper safety gear such as welding mask, long sleeves and heavy gloves
  • Safety glasses
  • Dust face mask
  • Drill for wire brush or rust scuffer attachments
  • Survey the damage and make a determination of the metal you need to cut out. Take your time and think it through before cutting away any metal and consider any bends you have to make. Sometimes you are best off to cut away additional metal if the cut will leave you on a flat area rather than a curved body line.

  • Put on your heavy work gloves before handling the metal along with safety glasses when using a cutting grinder. Cutting out the bad metal can be accomplished with metal snippers or possibly with your cutting grinder. This really depends on access. Survey the area behind your cut to be sure you won't be damaging another area of the car. Grind the cut out edges smooth with your grinder and clean the edges of the metal surrounding your cut out section with your wire brush, rust scuffer pad or sandpaper. You want at least 1 to 2 inches of clean metal surrounding the cut out areas and then spray the raw metal with the rust treatment spray.

  • Form your new pieces with the sheet metal. If you do not have sheet metal bending tools you can be creative and use a standard vice on a work bench or the edge of a table to make a bend or use a dolly or anvil. You can also use steel plumbing pipe to form your metal over if you need a round type of bend. The 22 gaoge can actually be bent by hand to some extent as well.

  • Special body repair hammers and dollies will help you shape and pound out your metal. The better you fabricate will mean less work later in the smoothing out stage using body filler.

  • See the picture, new metal needs to be installed on both sides of the remaining lower section. In some cases it is easier to drill some pilot holes and use sheet metal screws rather than weld if the screw heads will not be seen. You can also use screws even if they are out in the open and then use your grinder to grind down the screw heads to below or flush with the surrounding surface. Welding is quicker, but you must have clean metal surfaces and reasonable access. Standard vice grips will usually work to hold the metal in place as you weld it or screw in place.

  • Fill any gaps with liquid metal from a tube, JB Weld or epoxy after welding and then grinding down high spots, or if you used screws, and you have grinded down the heads flush to the surface. These products will also work well to fill in small holes.

  • Use the trim as a guide (as in this picture) to help you stay in proper contour. Always save any bad metal cut out to use as a guide before discarding.

  • Use Bondo body filler to cover your welding seams after your metal is in place, level surfaces out and also for any final shaping or building up you may still need to do.

  • Use a scraping tool if needed to bring down any high or sharp spots from the hardened bondo and then use 60 grit sandpaper on a power sander to get your work as level and smooth as possible. Follow up with hand block sanding using 60 grit followed by 120 grit sand paper for further smoothing and leveling. Always wear a dust face mask when sanding or painting.

  • Spray high build primer to better see where you are at and then work with spot glazing compound for filling holes or cracks and also for minimal height building, applying in thin layers, allowing to dry between layers. Use a straight edge ruler to be sure your work is level and you can also use a second color of primer during block sanding for easy identification of low spots.

Tips & Warnings

  • You will get a smooth straight cut with the grinder versing your snippers, but sometimes you can't get proper access with the grinder where a snippers will allow you more movement.
  • Allow Bondo to dry overnight before sanding down.
  • Save any old metal you remove to serve as a guide in forming your new metal.
  • Try to cut out metal in an area which will leave you a flat surface to work with rather than a body line curve.
  • Always wear proper gear when welding and grinding.
  • Work in ventilated area.

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