BUMPER COVER REPAIR
This method works on the bumper covers of the '80s & '90s, and most likely all plastic covers.
I made contact with Danny several years ago and the following is the write up provided when my Allante bumper got busted.
For reference, the trade name for the plastic utilized for Allante bumpers is XELOY.
provided by Danny Yunker
The best method of repair is to use 3M 5901 Flexible Parts Repair Material. It is much stronger, and easier to work with than the Sem Flex Weld. The entire process will be a combination of repair materials and methods.
First, any ridges or plastic that is raised, must be removed. Use a razor blade and trim the material away so that the surface is flush. Clean the area well. I prefer to use DeNatured Alcohol for this purpose, but any quality surface prep agent can be used.
The area should then be sanded to heavily scuff up the surface to promote good adhesion of the repair materials. 80 grit sandpaper works well for this, you can also use this sandpaper for sanding of the Flexible parts repair material. If you have gouges or grooves in the plastic, the surface areas inside these grooves must also be sanded, a Dremel Grinder works well for this.
If you have holes all the way through the plastic, place masking tape on the back side of the bumper to hold the repair material in place until it sets up.
Place the Flexible parts repair material into the hole and damaged areas and then place 2" wide masking tape over the compound until it sets up. This will not only hold it in place, but will also smooth it out so that much less sanding is required.
You will need to purchase a couple of items from a local Hobby store for the rest of the process. You will need a heavy grade "Super Glue" or Cyanoacrylate a product called "Zap" works well, but Hobby Shops will carry different brands which all work the same. You will also need a fine mesh Fiberglass. Heavy fiberglass, found in parts shops is too heavy and thick and will leave a "Lump" in the finished job.
Use the "Super Glue to hold the edges of the Flexible Parts Repair Material in place after it has been sanded smooth, and finish sanding the material after the glue has set up. Make sure the entire surface is smooth, uniform and reshaped according the the original shape of the bumper. Cut the Fiberglass mesh about 1/2 inch larger than the hole and secure in place with "Super Glue. Make sure that the fiberglass is completely soaked with "Super Glue" and allow it to dry.
You can also get an accelerator for the "Super Glue" to make it set up instantly if you want. Do this to both sides of the bumper. Sand the visible side smooth and then apply primer and finish coat to match your bumper finish. You will have the strongest repair, with the least cost. I hope this has helped. If you have questions, email me.
I have played with JB Weld and found that it does do a nice job on rigid parts. The only problem that I have had with it is the curing time required. Even the "quick set" sometimes does not set up fast enough for me. This is probably because I made these types of repairs for a living, and needed products that worked very fast. I would not recommend using it on flexible items because it tends to crack when flexed.