Plastic Grille Repair"Grilling" a GM to perfection
During the late Sixties, most domestic car manufacturers started using ABS plastic for many body parts. There were several reasons for this, the most blatant of which was cost. Why are you not surprised? Reducing vehicle weight was the second major reason, and plastic seemed the logical way to do it.
One area they addressed is the front grille. It would be damaged in an accident whether it was metal or plastic, so why not damage cheaper-to-replace plastic? However, as the plastic ages, it becomes progressively more brittle from UV rays, ozone and temperature changes. After 30-plus years, this 1969 GM plastic grille was showing its age, full of cracks and discoloring. For the dedicated restorer, fixing an original part is an important part of the process, so we'll give you a couple of hints on how to accomplish this task. The investment is small and the rewards large.
After removing your grille and any metal trim, carefully inspect the piece for broken contact points, stress cracks or dings from rocks and the like. This grille had been seriously damaged from above, either by something falling on it or someone leaning heavily on the top edge. After a thorough inspection, we determined that automotive body filler should be used to patch some of the cracks and a bonding agent used to glue the badly broken areas back together. Since some of the mounting tabs have literally been broken off, we will have to do some fabrication to fix the damage.
We used a grinding tool to enlarge the cracks and broken areas in order for the body filler to get a better bite on the surface. A larger and deeper contact area than the small original cracks will provide a better adhesion base for the repair. The material will flow into the grooves we created and flow completely between each piece. Once the material has hardened, any overlap or runs can be sanded from the surface. Use caution with the grinder as you can cause more damage than you're trying to fix with a quick slip. Simply take your time and tread lightly.
We followed the mixing instructions and applied the pasty body filler to the smaller cracks. You can control the speed that the filler sets up with the amount of hardener you use. The bonding agent has more of a liquid consistency, so we used it to fill and glue the big cracks. If you have trouble keeping the sections under repair together, try using tape to hold the parts until the adhesive dries. We allowed all the materials to cure overnight. A mounting point at the rear was broken off completely, so we used a combination of materials to glue it back in position. It isn't pretty, but it is holding and invisible.
Once the various materials are thoroughly dry, you can sand them smooth. If you didn't get the area completely filled the first time, an additional application of filler might be required. We used 150-grit paper to cut the filler and then smoothed the area with 400-grit. The smaller cracks are filled and the major crack at the top seems to be secure. Obviously, any repairs that are not going to be visible need not be sanded. Once all the repair work is done, we will paint the complete grille black, obscuring most of the sanding work and rough-looking areas.
One of the important metal-trim mounting points was broken and needed repair in order to secure the trim. The mounting pin on the chrome trim can now pass through this washer and be secured with a speed nut. There is usually a solution to the simplest problem; you just have to be creative. Before the glue that secures the washer dried permanently, we positioned the trim to make sure all the mounting points would work without adding additional stress to the grille.
With all the repairs finished, we scuff-sanded the entire grille with an abrasive pad prior to painting. After wiping the residue from the surface, we proceeded to add color to the plastic. We are using a semi-flat black enamel and applying the paint in several light coats. It's a good idea to give the areas that were repaired a quick primer coat prior to painting. After several coats, allowing 10 minutes drying time between each, the plastic looks like new again. With the polished trim installed, it will look like it just came out of the GM box. Allow a weekend for the entire project, most of which you can spend watching the adhesive dry.