How to repair a cracked car bumper

How to repair a cracked car bumper

Us, DIY guys like to save some money and do some car body work ourselves.

This time I decided to fully repair my cracked car bumper myself. No one likes a nasty cracked car bumper. There are many ways to repair your cracked car bumper. In my case welding the plastic was the most convenient way.

For this repair method you will need:

  • A soldering iron
  • Some scrap plastic – ABS plastic would be the best, since most car manufacturers use ABS plastic
  • Sandpaper grit 80/240/400/600
  • Fiberglass body filler. Note: use fiberglass filler, because it’s way more flexible than regular filler, therefore more suitable for bumper repair
  • Primer, paint, grease remover and clear coat

Step 1: sand and prepare the damaged area

Make sure your damaged area is clear of any debris or paint. A lot of people who use this method make this mistake – plastic that is not clear of paint WILL NOT adhere correctly. I also recommend to use some degreaser before welding the plastic.

I used grit 80 sandpaper to get rid of old paint and other debris.

Step 2: weld the plastic using soldering iron

Do your best to hold the cracked parts in the correct position. You can use clamps or tape to make sure everything is aligned. Heat both sides and weld some extra ABS plastic in. Don’t make it too bulky and don’t make it too thin. Try to keep the original thickness. It is very hard to get your surface even, don’t bother too much because you will fill it with body filler afterwards.

Step 3: sand off the extra plastic and apply body filler

Don’t sand using bent sanding paper held in hand. Use sanding block to achieve nice and even surface. Don’t mind the 80 grit scratches in plastic, now it’s time to clean the surface again. I recommend using compressed air and a degreaser. If you can’t use compressed air – clean the surface thoroughly with clean cloth and a degreaser.

Now you’re ready to fill the grit scratches. Carefully mix the correct ratio of fiberglass putty and its hardener. Then apply fiberglass on the surface using bondo spreader or an old plastic card if you’re on a budget. Give it few minutes to flash(see when the bondo’s color becomes slightly lighter and matte). Use 240 grit sandpaper on a sanding block to even out the surface. If the shape is far from the fine shape, use more aggressive grit sanding paper.

If you have to create a re-create a line or other design element feel free to read how to do it on my article.

Step 4: primer and final fine body filler

Spray the repaired area and some of its surroundings with primer. Wait for the primer to flash and sand the surface using 400 grit sanding paper on a sanding block. If the surface looks ready you are ready for the final preparation. If you can’t tell if the surface is ready spray some visible color spray paint and lightly sand the area again. The idea is to sand off the spray paint color without sanding of the primer to achieve a perfect surface and adhesion.

Step 5: painting and enjoying your work

Paint the surface, wait for it to dry and enjoy your work. I have wrote a post about car painting and my setup, you can read it here.

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