DIY Repair Job: Fixing a Cracked Bumper

man cleaning his car

Repairing a cracked car bumper is the perfect example of a DIY project  that you can do with plastic welding equipment. Doing these types of repair jobs on your own can save you hundreds of dollars that would otherwise be spent to get the bumper fixed at a body shop.

The following is a simple step-by-step guide for repairing a bumper using a hot air welder and plastic welding rods.
  1. Clean the repair area with plastic cleaner. Apply a heavy coat and wipe the area clean. Be sure to wipe in one direction to avoid re-contaminating the work area. Use a Dual Action sander to remove any paint and primer coatings until the bare plastic is exposed. Follow this process on both sides of the crack and all along the bumper crack itself. Once the area has been cleaned, blow the dust away with compressed air.

  2. Align the damaged pieces along the crack and apply aluminum body tape on the underside of the bumper. Aluminum tape is strong enough to withstand the heat of the welder. Use a plastic body filler spreader to optimize adhesion and squeeze out any air pockets under the tape. Be sure that you apply tape along the entire crack, especially the top, to keep the work area aligned while welding.

  3. Using a rotary tool with a tear drop-shaped bit, grind along the crack line to create a groove for the welding rod.
  4. On the back of the bumper, find the symbol that corresponds to the plastic welding rod that is appropriate for this job.

  5. Set the welder for the correct operating temperature based on the plastic identification codes. Use the welder to heat the tip of the rod in the base material groove until the two plastics bond together. Apply consistent downward pressure on the rod as it melts along the groove to ensure a strong bond. Continue melting the rod until it has completely filled the crack.

  6. Allow the plastic to cool, then remove the tape from the underside of the bumper. Repeat steps 3-5 until both sides of the crack have been filled.

  7. Grind away excess filler plastic until the filler line is slightly below the level of the bumper plastic. Sand away any high spots or imperfections so that the epoxy filler is able to bond properly. Apply adhesion promoter to any exposed plastic.

  8. Mix the epoxy filler parts in equal proportions. Use a plastic body spreader to mix the two until you have a uniform color with no streaks or air bubbles.

  9. Apply the epoxy filler to the repair area and allow at least twenty minutes for it to cure properly. Sand the filler so that it matches the level of the surrounding plastic.

  10. Sand all areas of the bumper where primer and topcoat will be applied. Blow the dust away so that you have a clean surface area. A light coat of adhesion promoter will help the paint stick to the plastic. Spray primer on all areas to be painted, then finish the job with a topcoat layer.

You may find that you’re not ready to invest in expensive welding equipment right away, but a good place to start is with a used ultrasonic welder or pre-owned plastic welding equipment that will allow you to practice and hone your skills on DIY projects.

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Please feel free to contact Ella Gray at with any questions.

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