32 Steps to Painless, Profitable Plastic Repair - BodyShop Business

32 Steps to Painless, Profitable Plastic Repair

Many repairers pass on plastic repair and instead, opt to replace, sending an easily repairable part to the landfill. Why?

Ever noticed that window crank knobs on the early 1940s vehicles are plastic? So are the column gearshift knobs and some dash and other interior trim.

Plastic has been used in automobiles for a long, long time. How long? Well, I’m not really sure, but probably 60-plus years.

Since the inception of plastic, vehicle manufacturers have steadily increased their use of it – both on interiors and exteriors. With this increased usage comes the inevitable repair challenges. (“Challenges” sounds so much more positive than “problems,” don’t you think?)

Why do car manufacturers insist on plastic as their material of choice? Think about it for a minute. You’re getting closer. Yeah, that’s right! I knew you’d come up with the answer.

Economics … a.k.a. money.

The OEMs – in their drive to control costs, provide the variety the car-buying public demands, reduce weight for fuel efficiency and eliminate corrosion – have found plastic to be a most useful medium to work with.

Lucky for us, plastics can be successfully repaired – and profitably repaired, too. Still, I know that many of you out there bypass a lot of plastic repair and, instead, replace an easily repairable part.

You’re probably thinking that it’s better to replace that part than to repair it because of potential warranty problems and cycle time concerns. But is it truly better?

Let’s say you’ve got a nice, new, silver sport model with a small tear and some gouges about a foot on each side of the centerline on the lower section of the rear bumper cover. The cover has wraparound sides that adjoin the quarter panels. The upper portion of the center section of the cover also adjoins the deck lid. The color match is dead on … now. If we replace, we’ll have to blend both quarters and the deck lid. We’ll also need to disassemble the back half of the car for paint. We could do as the insurance company suggests and just paint the cover, but you know it “ain’t gonna” match, so that’s not an option – for quality’s sake.

We can fix this. It’s simple really, and it’ll be a better job (plus one less thing we’re throwing away). Let’s get started.

1. OK, let’s take off the cover and strip it down for painting. We’re going to be professionals and place it on some saw horses, plywood, a blanket and some 36-inch masking paper. Why? Because we’re here to repair, not to create damage that needs to be repaired. Yeah, I know. This will take a technician five minutes to set up, but how long is it going to take for him to repair the scratch in the wraparound side of the cover that fits next to the quarter panel, which now needs to be prepped for a blend? Get it off the garbage cans! Give yourself every opportunity possible for success.

2. Wash down the part first with a water-based cleaner or warm soap and water. Don’t use a solvent-based cleaner! This is dangerous. Just a few months ago, a tech was burned when he was washing a plastic part with a solvent-based wax and grease remover. Static electricity ignited the rag in his hand. Startled, he dropped the open solvent can that he was holding in his other hand and, yep, we had a fire! Don’t do this and don’t allow your techs to do this.

3. Once the part is clean, inspect it for all of the damage. We have a large dent with one 30-mm tear through the cover at the center of the dent, along with several gouges.

4. We’re going to try to block out the gouges first, to see if they need any filling. We block them down with some 150 grit. They sand out, with the exception of two of them that are a little deep.

5. We hook up our heat gun to warm up the two scratched areas. We’re not going to burn the bare plastic, just warm it until it’s easily moveable from the backside with a glass bone or a paint stick. If you have any low spots or dents under the scratches and tear area, warm them and move them out to their original undamaged positions.

6. Push out in the area of the scratch, and you’ll see it move.

7. Cool with an air blower or a cold, wet rag.

8. Now, block it a little more. Hey, there went the scratches. This will work if the scratches aren’t too deep. If they are deep, you’ll need to identify the type of plastic and then fill them with a two-part filler. We use epoxy in our shop, but urethane is also available.

9. Follow the repair material manufacturer’s instructions religiously. This will determine your ability to succeed in plastic repair and refinishing. The plastic repair process isn’t a forgiving one, so you must meticulously follow instructions and directions.

Don’t mix different brand-line products. Stay within your paint manufacturer’s line of products. For example, don’t use one paint company’s adhesion promoter under another company’s primer surfacer.

Some adhesive materials have built-in adhesion promoters that really do seem to work. This means that you can eliminate the step of applying an adhesion promoter prior to the repair material.

In trying to make sure that my adhesive filler adhered properly, I applied adhesion promoter prior to the application of some epoxy filler that contained built-in adhesion promoters.

Once again, I shot myself in the foot. It wouldn’t feather back without peeling. So, I decided to read the label on the two-part epoxy adhesive filler material. (What a concept, eh?) Hmm … it says no adhesion promoters needed. Yeah, but I wanted to make it better. I didn’t – because it didn’t need to be better. It was designed and engineered by chemical engineers to be the best it could be! So why am I, a collision repairman, trying to improve on a chemical engineer’s directions? Gee, in that light, it does seem kind of stupid. I think I’ll just follow the instructions. My point? Don’t try to improve them. Just follow them.

And guess what, when I followed the instructions, heh, heh … it worked. It feathered back real nice. Hmm…

10. Let’s identify what type of plastic bumper cover we’re working with. Our two most commonly used are urethane or polyolefin. There are some made of polycarbonate, but they’re rigid. This one’s flexible.

Plastic identification marks are useful, and I encourage the manufacturers to put them on the backside of all the parts they produce. Unfortunately, they aren’t on the backside of all parts, so we’re forced to use alternate identification methods. It’s crucial that you be able to identify plastic to successfully repair and refinish it. We currently have two tests: a grind test and a float test.

The grind test requires grinding the backside of your repair part with a grinding disk (small) long enough to effectively abrade the surface. Observe the abraded area. If it’s smeary or smeared, it’s olefin based and will require a specific adhesion promoter to apply adhesive products or refinish products to.

If it actually grinds off in particles, it’s urethane. No adhesion promoter is needed for adhesive repairs, although some paint companies do require a specific adhesion promoter for urethane refinishing.

Another test I commonly use with success is the float test. Cut a sliver of plastic from the backside of the bumper cover you’re working on. This can be from an inside edge or from a reinforcing feature. Make sure it’s free from any paint or dirt. Place some water in a cup, and drop your sliver of plastic into the water. If it sinks, you have a urethane-based plastic. If it floats, it’s polyolefin. Use the recommended adhesion promoter for the type of plastic identified.

Manufacturers are moving toward more polyolefin-based plastics for bumper covers because the waste generated in the production process is very readily reconstituted and recycled back into the manufacturing process (much more so than urethane). Less waste equals reduced costs, which means more profit. This is a good thing.

A grind test indicates that this cover is polyolefin. This information allows us to determine the type of procedures to use for this repair.

11. Let’s get to that rip. V-groove each side of the tear with a carbide cutter bit in your die grinder or drill motor. Do the backside first. Make your groove at approximately 45 degrees on each side. Abrade each side of the tear about 2 inches. You may do this with your cutter or some 80-grit sandpaper.

12. Clean the area with plastic cleaner and properly dry. Clean, compressed air – free of water or oil – can help.

13. If the surface of the tear is uneven, use some aluminum-repair tape on the reverse side of the weld area. This will help to hold each side of the weld in proper alignment.

14. Pre-heat your welder and dial it to the correct setting. We’re ready. We’re going to weld it with an airless welder, although it can be repaired with adhesive products and reinforcing cloth, too. I like plastic welding. We’re going to use the universal-type welding rod that was designed to adhere to most plastics, but especially polyolefins. Universality was important because of the different compounds of olefins.

15. Place a piece of the filler rod in the tear. Use the shoe of the welder to heat and spread the rod into the tear. Be careful not to use too large of rod pieces at a time to avoid just covering the surface without bonding with heat from the welder shoe. Since the rod is flat instead of round, we have to carefully heat and spread the rod a little at a time. With urethane, you have a round urethane rod, which you push through a tubular opening in the shoe. Spread the filler rod material about 1 inch on each side of the tear. Build it up to approximately 1/8 of an inch. Once you’ve covered an inch on each side of the tear, stop.

16. Leave the heat on your welder in the proper setting and put the welder on the rest bracket.

17. Cut a 1-inch wide, 2-inch long strip of stainless steel reinforcing screen (this material is available from your welder supplier). Place the strip of screen on top of your weld area. Center it.

18. Push down on the screen, and then heat it until it sinks into the weld rod you deposited on the surface of the tear area. When it’s firmly attached, add more rod to cover the screen completely. This provides a very strong reinforcement for the exterior surface weld you’re about to perform.

19. Turn the cover over and feather edge with a D.A. an inch on each side of the tear. Use the grit recommended by your paint company for primer-surfacer. Take it down to bare plastic.

20. When you’ve achieved a 1-inch band all the way around the tear, pick up your die grinder/drill and V-groove the front side of the cover into welding rod on the backside. Yes, right through the tear into the rod we deposited on the backside. Again, bevel 13 mm on each side of the rip.

21. Use a razor blade to trim any “threads” that might occur in the grooving operation.

22. Now we’re ready for our exterior surface weld. Pay particular attention to feathering the edges carefully so they adhere well, and try to achieve a sufficient height to allow for finishing. (If your cover is urethane, the weld process is even easier. It’s the same basic procedure – minus the reinforcement strip. With urethane, reinforcement usually isn’t required for this type of repair.)

23. Let it cool, and then cut the surface down to level with a D.A. on grind or with a small disc in a die grinder. Maintain a low speed. It’ll save time.

24. Finish sand by hand. This job doesn’t need additional filler. The rod adheres and feathers very well. Final sand on block with 150 grit.

25. Properly clean the surface.

26. If you have any small defects, fill them with a two-part filler suitable for this application and then sand and feather smooth.

27. Apply the appropriate adhesion promoter. Follow instructions and recommendations for adhesion promoter prior to filling and priming with primer-surfacer. (If you prefer to repair with adhesives rather than welding, reinforce the backside after prepping similar to how we did for welding. You’ll use cloth instead of a metal screen. Do both sides as previously mentioned. Use adhesion promoters as directed. Clean your surface as recommended using the proper cleaners developed for plastics, sand the adhesive and finish for primer.)

28. We’re ready for primer. When you prime, keep the primer small to avoid blending onto the car itself.

29. Blend out the paint carefully. Blend small and away from the areas adjoining the adjacent panels.

30. Clearcoat the entire part.

31. Polish the adjacent quarters for gloss.

32. Reinstall the part. And we’re done! This is probably the most common plastic repair out there, and it’s a good one to do. The repair looks great. The customer’s car still has its original paint, and we’ve turned around the car in good time.


Writer Mike West, a contributing editor to BodyShop Business has been a shop owner for almost 30 years and a technician for almost 40 years. His shop in Seattle, Wash., has attained the I-CAR Gold Class distinction and the ASE Blue Seal of Excellence.

You May Also Like

Are You Ready to ROCK in 2023?

Do you know a “rockstar” in the automotive aftermarket? Then it’s time to nominate them as a Vehicle Care RockStar!

Unless you have been on a remote desert island the past few weeks, you’ve likely seen some intriguing teasers for the latest brand launched under the Babcox Media umbrella — Vehicle Care RockStars. If you have seen it, I’m sure you’ve got some questions.

It can be tough to articulate exactly what defines a RockStar. Is it Mick Jagger’s swagger? Eddie Vedder joyously stagediving into a crowd? Eminem’s clever lyrical prowess or Beyonce’s ability to inspire viral TikTok dances? Elvis’ upturned lip? Is it Slash’s iconic top hat and leather jacket? Dave Grohl’s infectious anthems?

Plastic Repair: A Solution to the Parts Shortage

If you can’t get parts, then it makes sense to repair them. So maybe it’s time to dust off the old plastic welder and two-part bumper repair adhesives.

Vehicle Structures: A Mixed Bag

By now, we all should know that vehicles today are made from an amalgam of different materials that require identification and research.

Auto Body Welding: Look Before You Weld

Don’t just grab and go; are you looking up the OEM procedures before welding?

STRSW: From Terminology to Technique

Plug welding and spot welding are not the same, but many use these two terms as if they’re interchangeable.

Other Posts

BodyShop Business 2022 Executives of the Year

This year’s Single-Shop award winner is Michael Bradshaw of K & M Collision in Hickory, N.C., and the Multi-Shop winner is Matt Ebert of Crash Champions.

Vehicle Calibrations and Mechanical Repairs

Whether you’re replacing a radiator or repairing collision damage, deviating from OEM requirements will make a shop a target for blame should something go wrong.

Preparing the Collision Industry for Electric Vehicles

Today’s electric vehicle/hybrid revolution combined with the lightning-speed proliferation of ADAS features has made training essential.

Conducting Collision Business: It’s a New Day

The goal is not to declare war against insurers; it is to declare independence for your organization so that you’re able to provide the highest level of service to your true customers.