Polyurethane Bumper Repair

Polyurethane bumpers like this old Camaro's are pretty rare on late model cars, but with more people restoring cars from the 70s and 80s, there's a need to be able to repair and restore polyurethane. This Camaro bumper has seen better days. It has some rotted and crack areas. In this video, we'll show you the process of how to repair a rotted-out area and a torn bolt hole. After the welds are done, we'll show you how to smooth the surface with our Flex Filler epoxy filler and our flexible waterborne primer surfacer.

Polyvance was formed in 1981 as Urethane Supply Company to address the needs of bumper recyclers and to supply products to repair urethane bumper covers. Around that time, many people did not think urethane bumpers could be repaired. We proved they can be repaired.

Polyurethane is a thermoset plastic. In the molding process, two chemicals are mixed and injected into the mold. It forms a solid through a chemical reaction. The molecules form crosslinks throughout the solid like vulcanized rubber. Because of this thermoset polyurethane is not meltable. You will NOT be able to use the nitrogen welder on this type of plastic. You can repair it with the airless plastic welder. This will not provide a fusion weld. The urethane welding rod is used more like a hot melt glue.

You can use our Mini-Weld Model 7 or the integrated airless welder that is part of our nitrogen plastic welding systems to perform the repair. These two options are recommended because you need to be able to control the temperature of the welder.

How do you know if your bumper is thermoset polyurethane? Look at the back side of the bumper for the ID symbol. If you see “PUR” or “RIM” molded in, you know urethane. If you can't find the ID symbol, if the backside of the bumper is yellow like this Camaro, you know it's urethane. Yellow bumpers are always urethane, but not all urethane bumpers are yellow. Some Toyota and GM urethanes can be light or dark gray, so don't go by the color alone.

This article can help you determine if your plastic part is thermoset polyurethane or a thermoplastic.

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.

• 1000 Super Prep Plastic Cleaner (three options available) OR 1001-4 EcoPrep Plastic Cleaner
• 6122 Heavy Duty Round Cutting Burr
• Aluminum Body Tape (several options available)
• 2000 Flex Filler (several options available)
• Waterborne Primer Surfacer (several options available)
• Polyurethane Welding Rod and an Airless Plastic Welder(choose a method below):
• Polyurethane Welding Rod with the airless plastic welding side of a nitrogen plastic welder. Our current nitrogen plastic welders include the 6027HT Standard Welding Tip.
• 5700HT Mini-Weld Model 7 (A 230V plastic welding kit is also available). The 5700HT kit includes a 15 foot starter roll of polyurethane welding rod and the 6027HT Standard Welding Tip.
• Note: Make sure you are using either the 6027HT Standard Welding Tip or the 6029 Bigfoot Welding Tip when using the round polyurethane welding rods.

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:

Polyurethane bumpers like this old Camaro's are pretty rare on late model cars, but with more people restoring cars from the 70's and 80's, there's a need to be able to repair and restore polyurethane.

Polyurethane is a thermoset plastic. In the molding process, two chemicals are mixed and injected into the mold. It forms a solid through a chemical reaction. The molecules form crosslinks throughout the solid, like vulcanized rubber. Because of this, thermoset polyurethane is not meltable.

How do you know if your bumper is thermoset polyurethane? Look on the backside of the bumper for the ID symbol. If you see "PUR" or "RIM" molded in, you know it's urethane. If you can't find the ID symbol, if the backside of the bumper is yellow like this Camaro, you know it's urethane. Yellow bumpers are always urethane, but not all urethane bumpers are yellow. Some Toyota and GM urethanes can be light or dark gray, so don't go by the color alone. If in doubt, call Polyvance for advice.

This Camaro bumper has seen better days. It has some rotted and cracked areas. In this video, we'll show you the process of how to repair a rotted-out area and a torn bolt hole. After the welds are done, we'll show you how to smooth the surface with our Flex Filler epoxy filler and our flexible waterborne primer surfacer to get it ready for paint.

The first step of any bumper repair is to wash it inside and out with soap and water. After letting the bumper dry thoroughly, clean the bumper again with one of Polyvance's plastic cleaning solutions, either the 1000 Super Prep or the 1001 Eco Clean. Spray a heavy, wet coat over an area about one foot square, then wipe dry with a clean paper towel.

In this rotted area, we'll grind out the sun-damaged urethane first with a carbide cutter bit. The key is to get down to some undamaged plastic underneath to serve as a solid foundation for the welding rod we'll apply to fill the v-groove. With your Polyvance airless welder set to the "PUR" temperature setting, melt the R01 urethane rod into the v-groove. Note that the welding rod itself is a thermoplastic urethane, so it melts. It has very good adhesion to thermoset urethane. Note that we are not trying to melt the base material. Just melt the welding rod into the v-groove. You can touch the bumper with the hot welder tip, but don't linger the heat or try to melt the bumper itself. Just press the melted welding rod into the pores of the plastic and press out any remaining air bubbles. Use the welder's heat to smooth the surface of the welding rod.

After you let the weld cool completely, rough sand it with 50 grit in an angle grinder first. Then sand with 80 grit in a DA sander to get the rod slightly flush from the surface. We'll fill the recess later with our flexible filler. Repeat this process over any other rotted out areas on the bumper. Cracks and tears can be repaired in a similar fashion.

Before we apply the filler, we need to fix this torn-out mounting hole. First use the die grinder to make a v-groove along the edge of the bumper. We'll fill this area in with the welding rod the same way we did before. To hold everything together, apply some Polyvance aluminum tape to the underside. This will support the melted welding rod as it goes over the gap. Then melt the R01 urethane rod on the area as before...melt the rod onto the surface and smooth it out, but don't try to melt the base material.

When it's cool, sand it smooth and prepare it for filler and primer. Polyvance's Flex Filler 2 is an epoxy two-part filler that's formulated to stay very flexible after it cures. Squeeze equal portions of parts A and B onto a mixing board. Mix thoroughly until the filler becomes a uniform gray color with no streaks. Press down hard as you mix to pop any air bubbles that have been created. Apply Flex Filler to all of the repair areas. You will have about five minutes of work time with the filler before it starts to gel.

Let the filler cure completely for about one hour before you sand it. Sand with 80 grit paper in a DA sander to profile, then finish sand with 180 grit. Sand the entire bumper with 180 grit paper. If this is a restoration job, you will want to sand all of the old paint down to the raw plastic to prepare the surface for primer. Apply one of Polyvance's high build waterborne primer surfacers over the entire bumper. Apply two medium coats with some flash time between coats. Let the primer dry completely, then sand it with 320 grit sandpaper.

Fill any remaining low spots with a flexible polyester glaze. Allow this filler to cure, then sand the bumper overall with 320 grit paper to prepare for the second coat of primer. Apply the second coat of primer. Repeat as necessary to fill all remaining imperfections and prepare the bumper for sealer and topcoat.

As you can see, our finished bumper is ready to be reinstalled on the Camaro, looking much better than it did before!