Repairing High-Spot Stress Cracks on Bumpers

Sometimes during a collision, cracks can occur in high-spots that are stressed by an impact that may have taken place in a different area of the bumper. This can leave distortions around the crack that must be removed before the plastic can be repaired. In this video, we will show you the step by step process of completing this repair using tools in Polyvance’s comprehensive line of plastic repair products.

Always wear proper safety gear while working!

Let us know your thoughts on this video by leaving a comment on YouTube!

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.

• 6125 Tapered Burr
• Aluminum Body Tape (several options available)
• Nitrogen Plastic Welder (several options available)
• Welding Rod (several options available)
  Note: Identify the plastic and choose the rod that matches the plastic you need for your repair.
• Plastic Magic Adhesion Promoter (several options available)
• 2000 Flex Filler (several options available)
• Waterborne Primer Surfacer (several options available)

Video Notes:

• 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:

Sometimes during a collision, cracks can occur in high spots that are stressed by an impact that might have taken place in a different area of the bumper. This can leave distortions around the crack that must be removed before the crack can be filled. In this video, we will show you the step-by-step process of completing this repair using tools in Polyvance's comprehensive line of plastic repair products.

STEP ONE: Heat along the cracked area using a heat gun. Do the same on the backside of the bumper. Use a blunt object to depress the high spots until they are flush with the rest of the bumper. Once it's cooled, you may want to use your thumbs to continue finessing along the crack. You may need to repeat the process of heating and applying pressure.

STEP TWO: V-groove along the crack, about halfway through the plastic, anywhere that you'll be applying welding rod. There might be paint cracks, as we encountered here, that in no way affect the structural integrity of the bumper. These will not need to be v-grooved or welded. Use aluminum tape to reinforce the backside of the weld area so that the heat from the nitrogen doesn't melt through the plastic.

STEP THREE: It's now time to begin welding. For smaller cracks, typically found on either end of the damaged area, you might want to use round welding rod. For the length of the crack, however, we used flat ribbon. Once you have finished fusing the plastics, use a combination of nitrogen and airless welders to smooth along the surface of the repair. Allow to cool before continuing. Remove the aluminum tape on the backside. There may be weak spots that will require additional attention. If that is the case, you can etch along the weak area with a die grinder, and then add a pass of plastic ribbon for additional strength. Since this part of the bumper will not be seen, no finish work is necessary. Immediately after you've completed the backside weld, flip the bumper over to make sure that you didn't alter the visible repair area. If you did, use a blunt object, as you did before, to depress any high spots that you might have caused.

STEP FOUR: Shave off any remaining high spots with a die grinder before you begin sanding. Sand using 80 grit sandpaper. Any paint cracks can be removed during this step of the repair. Sand again using 180 grit sandpaper to remove any remaining fuzz.

STEP FIVE: Spray with adhesion promoter, wipe with filler, and smooth.

STEP SIX: Allow the filler to cure, then sand with 80 grit sandpaper. Block sand using 80 grit sandpaper, and then again with 180 grit.

STEP SEVEN: Spray again with adhesion promoter and prime.

STEP EIGHT: Allow the primer to dry. Block sand using 320 grit sandpaper, and prime once more.

Due to the location of this crack, many technicians' first response would have been to replace the bumper altogether. But, as you can see, damage like this can be easily repaired using tools and supplies from Polyvance.

Look to Polyvance for all of your plastic repair product and training needs. We offer I-CAR Industry Training Alliance courses as well as other hands-on classes in addition to the video resources you can find on our website and on the Polyvance YouTube channel.