Plastic Working Techniques

When I was a kid, my introduction to the automotive hobby was building model cars. Like most of us, as my interests in the real thing developed, model building took a back seat. A few years ago, I got interested in them again, broke out the old tools, and started building. Fifteen additional years worth of patience paid off, with results far better than I ever got as a child.

When we got these taillights from our Road Kill Road Runner, they looked pretty rough, but I decided to see if they could be returned to at least acceptable condition for a driver vehicle. We weren’t aiming for NOS or concours quality, but we didn’t want ratty-looking pieces of junk, either.

In this article, our goal is to show you some basic plastic-working techniques that you can employ to save a trim piece for which you otherwise spend a bunch of money to replace. Let’s face it—for the majority of us, a $200 set of swap-meet taillights just isn’t in the budget for our daily driver. You can buy brand-new marker lights for around $12 each, but if you save your existing pieces, that’s $50 you can spend elsewhere. How about that plastic gauge housing?

We were quite happy with our results, the only unsatisfactory mend being a large missing piece we spliced in (see accompanying photos), but we expected that particular repair to end up looking that way when we began this endeavor.

For good plastic repair, you’ll need to visit your local hobby shop. Avoid shopping mall toy stores and find the best hobby shop you can, because they’ll have the specialized tools and the glue you’ll need. The most critical element of repairing plastic pieces is the glue. Use a quality, quick-drying cement that comes in a bottle with a precision applicator. Also, ask the store personnel if the glue you’ve chosen is sandable. Most model airplane glues are not sandable with satisfactory results. This will allow you to fill seams and cracks in the plastic, and make the repair undetectable. Also, model airplane glue can craze and warp plastic, and the fumes can haze the clear and tinted lenses, permanently discoloring them.

A good guideline to quick-dry cements is whether it will stick your fingers together on contact. You can also get glue accelerators, which make the cement dry even quicker, but we recommend against that kind of unforgiving speed for these types of repairs. To get these super-cements off your skin, nail polish remover works best.

We used a Craftsman rotary toolkit for this project, which made the job much quicker. These tools are great for cutting, polishing, and a host of other automotive applications. An assortment of small files and emery cloth for final sanding of the repaired areas is necessary. A small “Snap Saw” was used to trim the large patch piece for final fitment. You’ll also need some sort of donor lens as a source for the small chips of filler plastic. We thought using the same type of plastic material for our patches was better than using styrene (model car plastic) for the repairs, and used a trashed yellow marker lens.

For paint, we found that Plasti-Kote Medium Gray was a perfect match to our Road Runner taillights, and a Testors silver paint pen (available at most quality hobby/craft retailers) worked perfectly for the trim line on the marker lights. Good hobby shops also carry plastic polishing kits designed to buff model car paint and remove scratches from model car windshields, but will work on instrument lenses and scratched exterior lenses as well.

Follow along as we show you how we saved a pair of taillights and a marker light that were otherwise junk, and see if a couple of these tips can’t find their way onto your Mopar project.

This is the damage to the lights. The whole unit was originally injection-molded as one piece in red plastic with a clear reverse lens. The outer housing is red plastic, painted gray at the factory. Damage includes cracked edges...	...chipped corners, missing pieces and a crack in the housing...	...and a large missing chunk.
These are the basic model-building tools we used: a Craftsman rotary tool with cutoff wheels, sanding drums, and a polishing kit; a Snap Saw, assorted files, and quick-drying plastic cement. Not pictured are the emery cloth and a Testors paint marker.	The first order of business was to cement the crack in the housing. A rubberband held it closed, and cement was applied. It is important to use fast-drying cement instead of traditional model glue for two reasons. Model cement is nonsandable, but you can sand fast-drying cement to blend it and fill gaps. Also, the fumes from model glue will haze plastic (remember how the windshields on your model cars were always milky? That's why.), as well as distort it, if used in excess. Finally, the time it takes model cement to set is just far too long. Look for glues that will instantly bond your fingers together (we're not kidding), and include precision applicators. Should you glue yourself together, nail polish remover breaks the bond.	This was the most daunting part of the repair. A large chunk was missing from the housing. We squared off the edges with a small saw, for ease of fitting the patch.
A donor marker light was used for the plastic patches. We thought it was a good idea to use similar materials for the patches, rather than styrene (model car plastic) or the model putty you can buy in hobby stores. Like automotive plastic fillers, the putty can absorb moisture--the patched spot is weaker and can flake out.	We trimmed the piece to fit and glued it in place. Sanding was done primarily with sanding drums on the roto tool, with finish-sanding done with a light emery cloth.	Here are the major repairs. The corner and small piece missing near the crack were filled with small chips of the donor marker light, and contoured with the sanding drums. The only repair we're not sure about is the large patch.
Before we painted the taillights, we attached the small buffing wheels from Craftsman's polishing kit on the flexible shaft that came with the rotary tool, and polished the lenses. Use the buffer on the slowest speed, and be careful not to burn or haze the plastic by being too aggressive.	We also polished a side marker light. The marker light had no cracks, but the silver trim paint was in bad shape, and the plastic was hazy from 25 years in the sun. If you plan to do this in your home, in the winter, also plan to apologize to your wife for the lovely polishing compound fan-tail pattern on the floor. And walls. And ceiling. Always wear safety glasses while you sand or cut on the plastic, polish, and probably as you explain the mess to your wife.	A silver paint pen--also available at hobby shops--will bring the trim around this marker light back to like-new.
Use a light hand while applying the silver paint. This paint pen also works great on instrument clusters.	After masking off the lenses and painting the housings, a quick inspection revealed that a little more filling with the sandable cement would be needed for the repairs to be completely invisible. The large crack is no longer visible, and the chip it was missing is virtually gone as well.	The corner that was chipped is still detectable, but with some filling and sanding, it also would disappear.
The big squared-off chunk that was missing is still visible, and actually fairly obvious. A ton of hand-sanding and filling would probably make it disappear, too. But for a driver, this is acceptable. From 5 or 6 feet away, all these repairs are unnoticeable.	Here are the finished products. Plasti-Kote Medium Gray is about as close an over-the-counter match as you'll ever find for these '72 Road Runner taillight housings. From a distance, our repairs aren't offensive at all. The marker light looks brand-new with just a little polishing and fresh silver paint. All in all, we're pleased with our results, and these same techniques can be used on interior trim, plastic grilles, and any number of other areas as well.