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Sajeev
Community Manager

Community Question: That feeling when you stop putting off a task?

This is an update to the original question here, because I finally learned how to weld plastic. The moral of this story is that you must always learn new things, because it makes your life so much easier afterwards!  Wouldn't you agree? 

 

I have several issues with 30+ year old plastic on several vehicles. Or should I say "had" because I finally learned how to plastic weld?  The tipping point for me were two busted parts on my 1985 Ford Thunderbird.  So let's see what happened. 

Time to get meltyTime to get melty

Repair #1 was a little plastic disc that separated from the interior trim panel, which essentially snugs down the panel to the dashboard. 

 

So I fired up the "welder" to see how easy it would be to melt both parts so they would come back together. To be honest, it was so easy! The only hard part is waiting for the welder to heat up, and ensuring you do this in a well ventilated area. 

Plastic is really, really easy to work onPlastic is really, really easy to work on

Repair #2 was a similar issue but using leftover plastic as a patch panel. I cut the patch panel with tin snips, melt/weld into position, and then drill a hole (drill bit) and clean everything up (Dremel tool). 

 

The end result is a factory correct interior!The end result is a factory correct interior!

And here's the end result of repair #2: a factory part that will look better on the Tbird, only because it wasn't drilled to have a cheeseball LED light in it (for an aftermarket alarm). 

 

In theory, I coulda plasti-welded the drilled out hole too, but getting the texture and paint finish to match would have been challenging. Maybe next time? 

12 REPLIES 12
DUB6
Technician

   I salute you for tackling this project, Sajeev!  I've done some similar small plasti-welding jobs, but generally only in places that are hidden from view when the piece is installed.  Doing a visible dash panel is indeed bold.  I certainly agree though, that the texture matching is real rub - the actual welding is usually pretty simple.  Thicker stuff is obviously more forgiving than thin, which can easily warp or disfigure with the heat.  For really thin stuff, I typically just count on glue.

   I have - and I considered myself extremely lucky - used plaster-of-paris to "mold" the texture on a part, then placed the mold on some filler in a crack or hole, thus imparting the texture looking pretty close after everything has set up.  Lubrication to keep the mold and repaired surface from bonding together is key, and it can affect the look, and even contaminate the filler - so again, I've shied away from trying it on an area where the patch is very visible.  Guess I'm kinda chicken...

   Paint matching a colored molded plastic part is an entirely different animal.  Fortunately, many paint suppliers now have technology to scan existing colors and digitally analyze the spectrum to find what formula they need to create a match.  In the old days, it was just throwing darts at a board and lots of time and generally wasted paint.  At least you have a fighting chance now if you have a good supplier with good equipment close by.  Will probably cost you a few bucks, but might actually be less expensive than all the failed experiments with the old eyeball methods of years ago.

   The one thing I've not seen mentioned in most videos or write-ups about welding plastic that I think is important: some of the softer, more pliable plastics will become very hard and brittle after the melting phase.  So an area that needs some strength under flex conditions might just crack in the repaired area upon use.  I found this on fixing a gas cap that was pretty soft, and after I welded a crack, it broke after only a few uses because it had to be tightened down on the filler neck.

Sajeev
Community Manager

Thank you for your kind words, and the feedback! I especially like the plaster-of-paris idea. The brittleness isn't an issue this time, but now I see why the kit came with metal mesh...it was for cases just like that I assume! 

Rob1
Instructor

A talent learned Sajeev kudo,s looks great vintage plastic drives me up a wall look at it wrong and its just pieces on the floor and yes a vehicle that you have not owned from new many add ons over the years leave unrepairable holes /slots which can render the piece unsightly if not unusable the ability to repair to not noticeable is huge.R

TonyT
Instructor

Getting the paint color to match isn't that difficult these days with all of the speciality paints available, and you may be able to recoat the entire panel so the match is not an issue. The texture is indeed a different story, but this has worked for me in the past: Find a section of whatever you are repairing that is intact. Tape off a rectangular section of it with blue or green painter's tape and apply a thin coat of Vaseline to the exposed area and mix up a small batch of your favorite two-part epoxy. Apply the epoxy to the coated area, pressing lightly to ensure good contact. After it dries overnight, CAREFULLY lift it off and you should have an impression of the surface.  After you have repaired the hole, counter sink it a bit. Mix up a bit more epoxy and fill the hole. Allow it to set up (just tacky to the touch) for about half an hour and then press your previously made "mold" onto the repaired area. Presto, matching texture that should match the rest of the panel. Clean the panel with some rubbing alcohol, prime and paint. Practice on some scrap pieces you brought home from the salvage yard until you are happy with the results. It won't be perfect, but it will look great from three feet away once painted.

JHaydon
Intermediate Driver

Nicely done!

 

Does learning to weld metal count?  I had been begging friends to patch and re-patch the original, rusty, 30-year-old exhaust header on my racecar for several years before I finally took a torch welding class and bought a bunch of tubing... and a year or two later, I finally dusted off the tubing and got to work. It took me about a month of evenings and weekends but the result (A) fits and (B) still hasn't cracked.  I was so proud when I finished a 100-mile road race with MY header still in one piece!  

Sajeev
Community Manager

Not only does that count, it is far more complicated (and takes more practice) than what I had to learn. Great job! 

DUB6
Technician

Here, here!  One of the most handy talents any car-nut can develop is welding.  Thousands of applications (mine, my wife's, and those of 876 of my non-welding friends who found out I have a welder) have gone on my table. 😁 Tackling headers as a first project is TRES BOLD!  Sounds like they were well done...

DUB6
Technician

   I had a plastic welding job just yesterday.  A '97 Toyota 4-Runner had obvious coolant spray inside the engine bay.  We discovered a hairline crack along the front of the upper radiator tank - which is plastic!  Since finding a replacement rad on a Sunday was sketchy, I drained the coolant below crack-level, dried it, did a little prep work and plasti-welded it.  Is it a good long-term fix?  Nah.  But since the owner drives only about 1 mile to work each day, the car seldom reaches much temp, and so pressures inside the system are reasonably low.  It should hold until we can source and get our hands on a replacement...

Sajeev
Community Manager

Great job!  That will definitely work for a short while. 

fstntq
Pit Crew

You may be over thinking this.  You don't need unwieldy heat to melt ABS back together, Acetone or Methyl Ethyl Ketone work great.  (think modeling glue on plastic models)

This tab was 100% detached from the plastic door panel.  "Melting" a small excess piece of ABS in a glass jar gave me the reconnectable media and a few drops of the chemical on the mating surfaces basically preconditioned them to accept the ABS mortar.  The whole can now easily be  lifted by just the once broken off tab.  The process also works great for filling voids of nearly any size.  If you need colors other than black, Legos work great! 20210616_065504_resized.jpg20210616_065519_resized.jpg

Sajeev
Community Manager

Wow this is truly AMAZING!  Thank you for sharing this!  I think I have some not-so-valuable lego products I can sacrifice too. 

fstntq
Pit Crew

just "play" with varying mixtures of the ABS and the solvent until you get the viscosity you want for the mixture.  I use small cut up bits of ABS sheet, 1/8 x 1/8 inch and some old MEK I have had for ever.  I try for JB Weld consistency.  Basically as the solvent off gasses, the ABS reconstitutes and hardens. (both in your working jar and on the pieces you're trying to fix so working time can be short)   

You can also see some other work in the second picture on the lower left.  This process also works well for reinforcing  attachment spots that are weakening and close to breaking. You can Google some good videos on it.