Repairing Plastic

DogBunny

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I want to share a little self-taught skill that I have been honing for several years. Repairing plastic parts using fiberglass. Admittedly, our bikes, especially the earlier ones, don't have many plastic parts, and replacements can readily be found on eBay. But, I hope you all will find the process interesting.

Rpiller1.jpg

Here is a sample project, a 5th generation ElCamino right-side A Pillar Trim. On the left is what it is supposed to look like.

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Repaired. The dark area is plastic resin, the red is Bondo Glazing compound.

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Completed repair after spray-painting with SEM Color Coat. I'll show the step-by-step process in up-coming posts.
 
RRpiller1.jpg

Here's a really easy project to illustrate the process. These are rear pillar trims from a 5th generation El Camino. The project is on the bottom, on top is what it's supposed to look like.
This is the area where the front and rear pillar trims overlap -- there's a thinned-down area in the plastic where the front slides into the rear. It's so thin that it is prone to disintegrating.

RRpiller2.jpg

Note how bad the face is -- extreme surface cracking and powdering and loss of material.

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The first step was spraying the face with SEM Color Coat to stabilize it. I sprayed the back too, but this was a mistake -- the back was very stable and very smooth -- what I should have done was roughen it up to give it a tooth for the resin to adhere to. The repair still worked fine however.
Note that I am changing the color of these trim pieces from black to Camel Tan.
Next, I made a very simple "mold" for the resin using masking tape. The glue on the masking tape acts as an excellent mold release, meaning that the tape peels right off after the resin cures. I did my best with the tape to make the profile that I wanted, but it doesn't have to be perfect. You just need to create a scaffold to build on with subsequent resin applications.

RRpiller4.jpg

I poured a layer of resin on the tape. Then I laid down a single thickness of glass cloth, and topped it off with more resin.
I later decided that I should have over-lapped into the good area of the original trim more, which I did during a later resin application on a different piece.

RRpiller5.jpg

After removing the masking tape mold. The piece on the left is finished except for sanding and shaping. The piece on the right had an air bubble and a void that I filled with left-over resin while working on a different piece, and then it was also ready for sanding and shaping.
The resin that seeped under the masking tape is a good thing, further stabilizing the old plastic and integrating the old with the new.
Again, note how badly deteriorated the original pieces are.

RRpiller6.jpg

The finished repairs after spray-painting with SEM color coat.
The SEM is remarkable stuff, and is much easier to use than paint. I really, really soaked these pieces in order to fill in the cracks, but it still looks really rough. I considered using Bondo glazing compound, or some other compound or surface filler to skim coat the entire piece, but decided that would be too much time and material and trouble, especially for a piece that you can still buy new or on eBay.
Anyways, I'm happy with the repair, and it sure looks a lot better than it started out.
If you had an absolutely irreplaceable plastic piece that needed repairing, this would work. With enough time and patience, and using glazing and finish-filler compounds, any plastic piece could be made to look new.

I'll show a couple more repairs that I made, and will talk about the materials that I used and how I used them in up-coming posts in this thread.
 
Lpiller1.jpg

Here's one more repair that happened so quickly that I never had time to take a "before" picture. It's the left-side A Pillar Trim from a 5th generation El Camino, with a missing triangle-shaped piece of material.
I had some left over resin from working on one of the other repairs, so I just real quick slapped a couple of pieces of masking tape on the piece, laid down a coat or resin, added glass cloth, and topped of with more resin. I have literally spent maybe 2 minutes so far.

Lpiller4.jpg

Here's the result with the tape mold removed. I still have to fill in the edge and the tip of the triangle with more resin, but now I have something to work off of, where before there was nothing.

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Ready for paint. I probably should have used some Bondo glaze on it, but since this part of the trim is only visible if you look through the windshield, I thought that I could get away without it. Also, I found that feathering edges is tricky, and you can easily overdo it, because you're not feathering into hard steel like on a body, but into soft, crumbly, aged plastic.

Lpiller3.jpg

The finished repair. I would say that I spent about 30 minutes on this piece. Some are probably thinking "yeah, and it looks like it too." With more time and more materials, such as finishing fillers, this could have been made to look absolutely perfect, but that's not what the El Camino that these pieces went in is about.
 
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My tools and materials. I can get West System products locally at the West Marine store, and they are pretty widely available elsewhere.
The real advantage of this system is the pump dispensers. The ratio is 5 parts resin to one part hardener, by weight or volume, but the pumps do the measuring for you -- you just use one full pump of each. This eliminates measuring, or weighing, or messy pouring, and is great for making big batches.
For the repairs that I did in this thread, I only needed very small batches. I take a small plastic 3 ounce dixie cup, weigh it, pump a little resin in, weigh again, subtract the cup weight, divide by 5, and add that much hardener. You can make extremely small batches -- I have made them as small as 5 grams, but you need a scale that's good to a tenth of a gram to do this. I can literally pump one drop of hardener into the mixing cup at a time until the scale balances at where I have set the necessary total.
I have only ever used the 205 "fast" hardener. I've done some really big projects with it -- I first bought it to coat a pretty big outdoor wood table to make it waterproof -- and the fast still gives plenty of working time. Big batches cure a lot faster, so when you make the tiny batches needed for the plastic repairs that I did you get even more working time.
I bought that resin and hardener over ten years ago, used about half, and have been using the rest ever since -- it's still good.
Anyways, I'm not really selling the West System, but I am sold on the pumps. It is well worth finding a system that dispenses in this way, if there are any others out there. A gallon may seem like of resin and expense, but you'll use it for the rest of your life.
There are a lot of fancy additives available. In the past I have used the filleting materials in my pictures (405 and 407 -- these are fine powders) to thicken the epoxy to prevent running or to fill gaps.
If you've never worked with fiberglass before, that's a main purpose of the glass cloth -- it absorbs and contains the resin, helping prevent it from running.
 
Okay, so I did the math.
If you get the gallon kit of West System resin with 205 hardener and pumps included, and add for shipping, and add a little more for glass cloth, it comes to $150, and you get almost exactly 150 ounces of mixed resin, so the cost is almost exactly $1.00 per ounce.
I would say that I used about an ounce and a half for all of the repairs in this thread, plus a few square inches of glass cloth, so my cost of materials for the epoxy part of the repair was easily under $2.

trim.jpg

Here are the four pieces of plastic Pillar trim that I repaired, along with the front and rear metal garnish trims. I used two 12-ouce spray cans of SEM to paint everything in this pic. Normally, one can would have been enough, but I had to really soak the plastic pieces to get the paint to flow into the cracks.
My local auto paint supply house sells the SEM for $15 per can, including tax, so I have a total of $32 into this entire repair.
 
Nice write up. I'll echo your thoughts on the West Epoxy System. I used it professionally for 20+ yrs. It's good stuff.
 
Looks good!

A little off to one side of this but still might be related to plastic repairs. Has anyone had an experience with the UV cure glues. I have seen a few adds for the stuff and if it works as claimed it could be very useful. Probably just posting this will get a few more linked to my computer feed!

I believe they claim it was developed as an offshoot of the UV cured dental products. As someone who has a front tooth that has about the lower third of it made that way I can attest to how good that is! And some here might recall that an XS650 was involved in the need to replace the part of the tooth!
 
Nice write up Dog - from my experience there are a few things I’m gonna disagree with though haha. - the point of the glass fiber - it’s not there to keep the resin from running. It’s there for strength. Resin alone has almost no real strength. If you wanna thicken you’re resin get some microballons.

epoxy resin and chop mat is a notoriously bad combo in terms of bonding. Chop mat has a styrene binder meant to be used with a poly (or vinyl) resin.

All resin has a shelf life. If you are placing trust in it, 6 months from production date (not from when you bought it) if there is dust on the jug, move along...

Probably not a big deal with little trim dings but anything of importance use fresh poly. Also, woven glass will also greatly increase your strength even if it’s cheap Eglass that you can get at a big box store BUT mat will work fine on pretty much any auto part just make sure it’s a high mat to resin ratio (50/50 is ideal)

also - A UV cure poly will cure almost instantly when exposed to uv rays (the sun).
 
Nice write up DG, I’ve have laid a lot of glass in the past, it is amazingly easy to form into complex shapes, it is surprisingly strong and easy ( if incredibly dusty ) to finish. Good job! :thumbsup:
 
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