Busted! How to Fix Broken Plastic Trim

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.

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. 

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.

Supplies

Items needed to fix broken plastic trim:

JB Weld Plastic Repair, Kwik Weld, or Original epoxy

Masking Tape

Dupli-Color Interior Paint

Dupli-Color Truck Bed Liner Aerosol

Dupli-Color Adhesion Promoter

320-Grit Sandpaper

Wax & Grease Remover

Prepare To Repair

Cleaning the panel with wax and grease remover is the best way to get the part clean without damaging the plastic.

Cleaning the panel with wax and grease remover is the best way to get the part clean without damaging the plastic.

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).

We used some lint-free shop towels to clean the part. You have to wipe the wax and grease remover on and then wipe it off with a dry cloth.

We used some lint-free shop towels to clean the part. You have to wipe the wax and grease remover on and then wipe it off with a dry cloth. 

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.

Corners are a high stress area, cracks are common here.

Corners are a high stress area, cracks are common here.

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.

The crack was closed and taped up with masking tape as a backing for the epoxy.

The crack was closed and taped up with masking tape as a backing for the epoxy. 

Using the masking tape, we closed the crack and secured it.

The Fix Is In

JB Weld Quick Weld works great on metal, fiberglass and plastic. It is metered out in the proper ratios with the plunger.

JB Weld Quick Weld works great on metal, fiberglass and plastic. It is metered out in the proper ratios with the plunger.

 

The tube just measures out the material, it has to be mixed by hand.

The tube just measures out the material, it has to be mixed by hand.

Next, we mixed the JB Weld Kwik Weld. You don’t need much, just enough to cover the repair.

Next, the epoxy gets pressed into the split from the back side. This reduces the amount of finish work required on the visible side.

Next, the epoxy gets pressed into the split from the back side. This reduces the amount of finish work required on the visible side.

The epoxy was spread onto the crack, pushing it into the split.he 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.

After about 15 minutes, we removed the tape exposing the repaired crack. It could be left like this, but there is some texture loss that needs to be addressed.

After about 15 minutes, we removed the tape exposing the repaired crack. It could be left like this, but there is some texture loss that needs to be addressed.

 

The panel was sprayed with a white guide coat before sanding. This helps us see all the damaged areas.

The panel was sprayed with a white guide coat before sanding. This helps us see all the damaged areas.

Finishing

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.

In order to remove any loose material on the panel, we sanded it down with 320-grit sandpaper.

In order to remove any loose material on the panel, we sanded it down with 320-grit sandpaper.

 

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).

Plastic is hard to paint, as it is an oil-based product. Adhesion promoter helps soften the material, providing a chemical bond as well as a better mechanical bond for the paint.

Plastic is hard to paint, as it is an oil-based product. Adhesion promoter helps soften the material, providing a chemical bond as well as a better mechanical bond for the paint.

 

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.

Spraying the adhesion promoter is done in two medium coats, with 15 minutes dry time between coats.

Spraying the adhesion promoter is done in two medium coats, with 15 minutes dry time between coats.

 

Adhesion promoter requires two coats with a 15 minute rest between coats, and then a top coat within one hour.

 

Spray-on bed liner works really well for this process. experimenting with different spray distances, angles, and even mixing bed liner and bumper trim paint can yield different results to match grain.

Spray-on bed liner works really well for this process. experimenting with different spray distances, angles, and even mixing bed liner and bumper trim paint can yield different results to match grain.

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.

 

Several light coats are best when working with bed liner. Too much build up at once will not look right.

Several light coats are best when working with bed liner. Too much build up at once will not look right.

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.

 

Here you can see the various droplet sizing and how the grain is recreated.

Here you can see the various droplet sizing and how the grain is recreated.

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.

 

All done, the repaired door panel is ready to be re-installed.

All done, the repaired door panel is ready to be re-installed.

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.

We used the same process on all 4 door/rear seat trim panels so that they would match.

We used the same process on all 4 door/rear seat trim panels so that they would match.

To learn more about NAPA AutoCare, visit www.NAPAAutoCare.com.

about author

Jefferson Bryant

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.

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3 Comments

  • Susan Cintron

    March 7, 2016 at 1:18 PM

    Reply

    The interior plastic pillar molding that fits around the windows in the cab on both the passenger and drivers side of my VW Eurovan is sun damaged and cracks at the slightest pressure. I am afraid it will self destruct if I try to remove it for repair. Because of the condition of the plastic I think repairs would have to be done in place. Replacement parts are no longer produced. What do you suggest?

  • This guy

    November 21, 2016 at 8:22 PM

    Reply

    Susan,

    Experiment with fiberglass and mold your own.

    You can do it!

  • This guy

    November 21, 2016 at 8:31 PM

    Reply

    Susan,

    Also, consider having it 3D printed. Check with your local High/Tech school.

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