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.
Polyvance's Scuff Magic soap is a great product for preparing the surface for repair and refinish.
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 Polyvance's catalyzed polyester Putty Flex product.
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!