How to Fix Broken Plastic Interior Automotive Trim Panels
Unlike the classic American cars on the 1950s and earlier, modern automobiles are full of plastic. From door panels and dash pads to the engine cover, plastic is everywhere. While this may be an affordable way for today’s auto manufacturers to build cars, the fact remains that plastic simply does not last as long as metal. Eventually, these plastic components fade and crack, leaving you with the task of replacing it or living with busted parts on your car. But you can fix broken plastic trim if you follow a few steps.
The 1960s saw the biggest change over from metal to plastic. As metal became more expensive and plastic forming technology grew, the automakers quickly grabbed onto plastic as the material of the future. Not only is it cheaper to make, plastic components are much lighter and weigh a fraction of what metal counterparts would. By the 1980s, everything on the inside of a car was plastic. Pop the hood on just about any car made from the late 1990s and you will likely find engine components that are made of plastic. General Motors has even been using composite plastic components inside the engine itself. While our example repair here is on a classic muscle car, renewed interest in 1980s and 1990s cars means the same repair techniques can be applied as well.
There is not much you can do when composite engine components fail, that is usually a replacement item. On the other hand interior and cosmetic components are easily repaired if you take the time to work it out yourself. All you need are a few products that are readily available at any NAPA Auto Parts Store to fix broken plastic trim parts.
Items needed to fix broken plastic trim:
JB Weld Plastic Repair, Kwik Weld, or Original epoxy
Dupli-Color Truck Bed Liner Aerosol
Prepare To Repair
We had a pair of sun-bleached plastic door panels from a 1974 Dodge Challenger that were in need of some restoration. Over time, the sun eats away at plastic and eventually it starts to flake off, much like how steel rusts. In addition to the crusty surface, one corner on each panel had split. These panels are hard to find and expensive. Repairing the panels costs less than $20 and 3 hours (not including cure times).
The process begins with a quick clean up. The panels were wiped down with wax & grease remover. You can use window cleaner, or even soapy water, you just want them to be clean before you start.
Next, the crack was located and assessed. For this repair, the epoxy will be added to back of the panel, which makes the final finish much easier.
Using the masking tape, we closed the crack and secured it.
The Fix Is In
Next, we mixed the JB Weld Kwik Weld. You don’t need much, just enough to cover the repair.
The epoxy was spread onto the crack, pushing it into the split. The crack was then pushed together and taped again to ensure it would stay closed. The Kwik Weld hardens in 6 minutes, and fully cures in 4 to 6 hours.
Once the repair was complete, we sanded the panel with the 320-grit sandpaper. Anything more coarse than 320 will leave sanding scratches in the final finish. The goal here is to smooth out the oxidized layer, taking off the chalky plastic, leaving the good layer intact.
The sanding action removes some of the grain, though much of it was already gone due to the chalky plastic. We can’t replace the exact grain, but we can get pretty close with spray-on bed liner. Plastic is inherently difficult to paint, so we need to prep it well. First, it is cleaned with the wax & grease remover (you need to use this product for this step).
Next, we sprayed the panel with Dupli-Color Adhesion Promoter. This slightly softens the plastic, providing a mechanical bond that the paint needs to stick.
Adhesion promoter requires two coats with a 15 minute rest between coats, and then a top coat within one hour.
To recreate the grain, we need a paint that not only is durable, but also formulated for texture. There are many different paints that we could use for texturing. A light grain is best matched with bumper trim paint, but the heavy grain on the Challenger panel needs a larger texture, making the truck bed coating a better match.
The trick to spraying this stuff is to use several light coats, sprayed from 8 to 15 inches away. The distance gives the paint a chance to dry slightly in the air before hitting the panel. This means the droplets vary in size, the result is a simulated grain that mimics the original grain of the plastic.
The bed liner requires a minimum of 3-4 hours of cure time before touching, but you need to wait 24 hours before reinstalling them.
You might notice that the panels are black. Bed liner is always black, which while that works out well for black interiors, it might not fit your tan, red or any other colored interior. All is not lost, however. Once cured, the bed liner can be top coated with any paint to match your interior. That is all there is to this simple plastic repair and refinish project. This process is good for door panels, consoles, A-pillar trim, just about any plastic component that needs repair and restoration.
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Jefferson Bryant View All
A life-long gearhead, Jefferson Bryant spends more time in the shop than anywhere else. His career began in the car audio industry as a shop manager, eventually working his way into a position at Rockford Fosgate as a product designer. In 2003, he began writing tech articles for magazines, and has been working as an automotive journalist ever since. His work has been featured in Car Craft, Hot Rod, Rod & Custom, Truckin’, Mopar Muscle, and many more. Jefferson has also written 4 books and produced countless videos. Jefferson operates Red Dirt Rodz, his personal garage studio, where all of his magazine articles and tech videos are produced.
Great article, thanks
Thank you for this post!! I can’t wait to use it on my 79 Ford F-250 door panels!! Jo