Plastic Welding: Bumper Crack in High Stress Area

Many bumper covers have built-in stress areas that typically break in the same area, and often break without much force. Preparing it incorrectly could result in the bumper breaking again just when reinstalling the bumper on the car.

This Honda bumper cover is a good example. Any bending of the bumper is concentrated in this small area. We will repair this bumper cover with our nitrogen plastic welder.

Voiceover: Rachel Moore

Always wear proper safety gear while working!

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Products Used:

Note: This is a list of the Polyvance products that can be used to make this repair. This list does not include sanders, grinders, or other common tools you will need. If you have any questions, please don't hesitate to call technical support at 800-633-3047.

• Aluminum Body Tape (several options available)
• 6125 Tapered Burr
• Nitrogen Plastic Welder (several options available)
• Polypropylene welding rods
  Note: We used polypropylene here because of the identification symbol. Choose the rod that matches the plastic you need for your repair.

Video Notes:

• The voiceover is provided by Rachel Moore
• English Closed Captions have been provided for this video. Click on the CC button to turn them on or off.
• The length of this video is in no way representative of the actual time required to perform a complete repair and therefore should not be used for estimating purposes.

English Transcript:

Many bumper covers have built-in stress areas that typically break in the same area, and often break without much force. Preparing it incorrectly could result in the bumper breaking again just reinstalling the bumper. This Honda bumper cover is a good example. Any bending of the bumper is concentrated in this small area.

Align the break and apply aluminum body tape to keep it in alignment while you do the repair. Aluminum body type is very stiff and can withstand the heat from the welding process. On this repair, we doubled up on the aluminum tape to better keep it in alignment.

On the back side, expose new plastic with the die grinder and a Roloc disc. Next, v-groove along the crack line with the tapered burr. Aim the flow of air at the intersection of the rod and the plastic that you are welding. Be sure to melt both the rod and the existing plastic. On this particular weld, we are doing two passes with the rod. While the plastic is still hot, use the airless plastic welder to smooth the weld. To better distribute the bending forces on this bumper cover, lay down several passes of the polypropylene strip on the backside for reinforcement. Again, while the plastic is still hot, use the airless plastic welder to smooth the weld. Allow the weld to cool completely before starting on the front side.

Remove the aluminum body tape and use a tapered burr to ground a V groove along the crack line. Grind deep enough that you can see the weld of the backside. Aim the flow of air at the intersection of the rod and the plastic that you are welding. Be sure to melt both the rod and the existing plastic. On this particular weld, we are doing two passes with the rod. While the plastic is still hot, use the airless plastic welder to smooth the weld. Once the weld has cooled, you can sand the weld smooth. As you can see, the bending forces are no longer concentrated to the crack line, but are spread over a large area.