Plastic repair

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ProctorSilex
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Plastic repair

Post by ProctorSilex » Sun Mar 09, 2014 11:29 pm

I have had to repair the bumper and tail light on my Miata. Air cooleds don't have much plastic, of course, but I thought I would share the experience anyway. It had structural damage from an accident, scrapes from multiple mishaps, and I wanted to fill in the badge holes. A mounting tab on the replacement tail light had broken off during shipping.

I fixed the structure using this Horror Fright plastic welder. One of the brackets that holds the bumper on at the bottom was partially broken off. The bracket is thin and this air tool distorted it and the exterior surface behind where the bracket joins the bumper. It has been a while, but I am pretty sure I identified the type of plastic from codes molded on the inside of the bumper and chose the fill rods from HF accordingly. The fill rods were hard to join with the bumper, but they seemed to work mostly. I don't know why, but I get the feeling that it is brittle though it has held up to my pushing and pulling on the joint. This thing might work a lot better with practice. It is basically a highly focused heat gun and it does have potential. I wonder about the quality of the filler rod from HF more than the tool.
I do not have a picture of the bracket.

There was a deformation and a scrape at one corner. The scrape had gone completely through at one point. I first hit the indentation with a heat gun and pushed it until it looked right. Then I used Bondo's 280 bumper epoxy repair kit to reinforce the inside according the instructions. It comes with some plastic screen to help. I do not like this stuff. It is hell to get it out of the tube and you don't get much epoxy for your money, but you do get a baby spatula and the plastic screen. I have some filling work to do on the outside where I plan to use Bondo's 806 epoxy instead. It is a different formulation without the doodads, but it comes with more and should be easier to extract. It has fibers in it which the kit lacks.
I do not have pictures of the corner. It is a work in progress and I could take some if there is interest.
I also used the 280 epoxy kit to fill in the badge holes. I cleaned the holes and mushroomed them a little then taped over the outside with painter's tape. I filled in from the inside and finished it off with a piece of screen. I sanded the outside flush. Most of the holes filled well, but some had trouble because, presumably, I did not mix that batch thoroughly enough (giving Bondo the benefit of the doubt).
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I filled in some scrapes with the 280 also and plan to do the rest with the 806.
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I repaired the tail light tab according to this video on cheap plastic repair with a torch. Instead of rolling my own tools, I picked up this HF scraper set which has worked well so far for the outer side (have yet to repair the under side). This worked pretty well and I would recommend this for the structural repair of the bracket instead of the air welder. It will look ugly. I did this on the tail light because it will be covered by the trunk. I have been using bits of the destroyed light as filler. If I had known, I would have used this method to repair cracks in a late model Beetle heater fan box before selling it (heck, I would have kept it). By the way, the only non-rusting screen Home Depot had was aluminium which seems to be fine.
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The car's finish looks pretty rough now but at least it is back in one piece again and not lumpy and crinkly any more!

I hope this info is of some help to somebody.

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Piledriver
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Re: Plastic repair

Post by Piledriver » Mon Mar 10, 2014 4:44 am

FWIW, I have had excellent results with Duro Plastic Welder.
(Nothing works on everything)

I have used it for years in applications that shatter JBWeld (24 hour std variety=strongest) instantly.
It has some give to it.

It's actually sold under several brands, but it will always be called "plastic welder"

This is not some "plastic epoxy" , it's a methacrylic ester based adhesive chemically similar to ~locktite.
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Re: Plastic repair

Post by Ol'fogasaurus » Mon Mar 10, 2014 9:23 am

A couple of weeks ago the 'Truck Tech' show on Spike had an episode on this very thing. Along with PS's and PD's posts it might be worth while to look up that 15 minute portion of the show (http://www.spike.com/episodes/nz5f8e/po ... n-4-ep-002 The second part of the show deals with flipping a Grand Cherokee and that is where the soft bumper repair is shown).

Lee

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ProctorSilex
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Re: Plastic repair

Post by ProctorSilex » Mon Mar 10, 2014 3:22 pm

Searching for "duro plastic welder" was unfruitful, but "methacrylate ester plastic weld" yielded this and this.

I never knew that Spike had useful DIY info.

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SCOTTRODS
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Re: Plastic repair

Post by SCOTTRODS » Mon Mar 10, 2014 6:37 pm

ProctorSilex wrote:Searching for "duro plastic welder" was unfruitful, but "methacrylate ester plastic weld" yielded this and this.
did you price the special gun that squeezes out the stuff in those 2 links? Frickin' $411.00. The Product itself available as "case only" at 789 bux... SheeZ... :shock: :shock:

Rich people toys (Unless you work with the stuff at work... then the shop gun and spare glue is a little cheaper :mrgreen: )

By the way... Shopping ebay may turn up some more reasonable results too.

You can find the Devcon stuff on Ebay, and a gun for real cheap. Less than 40 bucks for a set up.
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Piledriver
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Re: Plastic repair

Post by Piledriver » Mon Mar 10, 2014 11:10 pm

Duro (or Devcon, same stuff made under license) Plastic Welder is ~$3-$5 at any Ace hardware store, or Autozone, probably many other places.
Comes in a cojoined-tube black dual syringe like an epoxy dispenser.

Unless you are glueing up large sections like putting a fiberglass boat together or such, the gun isn't needed.
(The stuff is perfect for jobs like attaching a steel thingamajig to a wood whatsit on a fiberglass thingie)

It is probably the "consumer" version of the stuff listed above.
It is considered a "super adhesive" because it sticks to almost anything, and it is as strong as hell.
(it is also probably the ~original version---I have been using it for >20 years)

Sadly it is only good to 200F, but for most uses, that is not an issue.

Some other stuff that is incredibly strong (and a bit expensive) is the 3M urethane adhesive they install windshields with.
Sort of like Shoo-goo from hell.
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SCOTTRODS
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Re: Plastic repair

Post by SCOTTRODS » Thu Mar 13, 2014 6:39 pm

Piledriver wrote:Some other stuff that is incredibly strong (and a bit expensive) is the 3M urethane adhesive they install windshields with.
I love that stuff... I use the white stuff every now and again. INCREDIBLE hold. Will de-laminate Alclad Aluminum Sheet metal. As long as you prep it right, it's unstoppable. I like the Bostik 1100 personally. Buy it online... If you open it and use any of it... toss the rest in the trash... it cures from exposure to AIR (The moisture in the air, really)

Image
I have found them completely missing more than once. - PILEDRIVER

Some pics of My Powder Coating work
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