Split Decision Split Corvette Bumper
Maybe you’ve been there, trying to drive your car into a corner too quickly or simply putting it in Reverse and cringing at the crunch. The resulting damage used to mean a quick trip to the auto-parts store for some inexpensive body filler and a can of spray paint, but modern plastic bumper covers-such as those used on C5 Corvettes-require an entirely different arsenal of products.
Fortunately for your bruised bumper, plastic-repair and -refinishing materials are widely available and reasonably simple to use. The repair job will involve grinding, sanding, sculpting, and painting, but it’s well worth the effort considering that the entire process should cost considerably less than your insurance deductible.
We recently had the opportunity to meet Dick Jacobs, founder of Duramix, a plastic-adhesive company that was purchased by 3M. Jacobs described the four main categories of plastics used in the automotive industry, noting that not all plastic bumpers are made from the same material. The type used on your vehicle should be easy to identify, as it is normally stamped on the inside of the bumper.
PUR (Polyurethane Plastic Rigid): Most Corvette bumpers are made of this material. It sands to a powder, does not melt when subjected to high-speed grinders, and is easy to repair.
PP (Polypropylene), PPO (Polyphenylene Oxide), and TPE (Thermoplastic Elastomer): These materials smear easily during sanding and melt like butter under a high-speed grinder.
TPUR (Thermoplastic Polyurethane Elastomer): These plastics powder when ground or sanded.
SMC (Sheet Molded Compound): Today’s Corvette body panels are made from this material. It looks like fiberglass, exuding a similar white powder. We will cover SMC repair in another article.
Which adhesives you need depends on the type of plastic in your bumper. Be sure to consult the counterperson at the auto-parts store so you know you get the right stuff. It’s also a good idea to stick with a single brand to ensure compatibility.
Believe it or not, the hardest part of this repair job may be removing the bumper. The screws that hold it on can be tricky to locate, hiding out under the taillights, behind the wheelwells, inside the decklid area, and above the exhaust opening. Once the bumper is off, be sure to do your work in a warm, dry place so the repair adhesives can cure properly. Our next projects will include an SMC repair and information on how to paint your newly repaired panels.
C5 Urethane Bumper Repair – Split Decision
Replace or repair? Fixing your damaged bumper should take only two hours or so once you’ve removed it from the vehicle. We chose to go this route.
The repair process begins with cleaning both sides of the bumper cover using a mild dish soap and water. Dry with unoiled compressed air and finish with a general-purpose adhesive cleaner to remove any remaining oil and wax. We used 3M’s General Purpose Adhesive Cleaner (PN 08987).
Prepare the front and back of the bumper using a pistol-grip die grinder with a 50-grit Roloc sanding disc (PN 01396). Prep these areas by “U” grinding and cutting away any excess material.
You may need to use a 700- to 1,000-watt hand held heat gun to relax the torn pieces and aid in realignment. When you’re done, quench the area with cold water.
Final sanding before repair should be done using an 80-grit dual-action sander to remove any particles and assist with adhesion. We used the 3M Hook It II System due to the flexibility of the pad.
Examine the repair area to verify that it lines up correctly.
Secure the front of the repair using Scotch Auto Body Repair Tape (PN 06930) to fit both sides together as precisely as possible. This will add support while you’re applying the patch material to the back of the bumper.
Using a 3M EZ Fix Flexible Patch (PN 05888), trim the patch to fit the repair, allowing a 11/2-inch overlap on all sides. If your repair includes the edge of the bumper, go beyond the edge by 11/2 inches. The excess patch can be trimmed off later.
Before affixing the patch, blow off the area with unoiled compressed air, then prepare it with Automotive Adhesion Promoter (PN 06396). Wipe the backside of the bumper where the patch will be applied, allowing a 2-inch overlap. Allow the product to dry for five minutes before continuing.
Remove the liner from the backside of the patch, keeping it as clean as possible.
Attach the patch to the prepared area, pressing it firmly; pressure will increase the bond strength. If the repair requires a bend to be made in the patch, use the heat gun to help make the patch material more pliable.
As you can see, the EZ Fix Flexible Patch makes for a very clean repair. It’s also quite easy to use.
Now it’s time to work on the front of the bumper. Carefully remove the tape, then clean the surface with a general-purpose adhesive cleaner to remove any oils and contaminants.
Apply a coat of Polyolefin Adhesion Promoter (PN 05907) and allow five minutes to dry. The adhesion promoter will also help with feathering during the sanding process.
Now it’s time to apply the Automix EZ Sand Flexible Parts Repair material.
When using any two-part material, it’s important to hold the dispensing tube vertically and remove all the air from inside the tube. This should prevent most of the pits that can form when small air pockets develop in the finished product.
Use a spreader to create a tight coat. Apply additional coats to build up the material slightly higher than the bumper cover. Allow 15 minutes for the material to dry before sanding.
Apply the Automix to the area to be repaired.
When working on a vertical surface, use a plastic bag to hold the material in place until dry.
Sanding should be done using an 80-grit dual-action sander or hand block. Use a higher-grit sandpaper to get the surface flat. If any imperfections remain, apply another coat of Adhesion Promoter and Automix EZ Sand Flexible Parts Repair Material.
When the material is level with the height of the bumper, change to 180-grit to remove the 80-grit scratches. To finish, use 320-grit to feather around the repair areas. The bumper is now ready for paint.
My Update: 4/2011
Looks like I am going to be trying this for my owie! I was going to just get a paint job soon, but I guess the idiot who didn’t tie down his load of crap thought I need a new bumper and windshield as well.