Plastic welding, any tips?

[Lorenz]

Ive been having a go at a spare bumper I bought aswell. It was a bit harder than I first expected and time consuming so you have to be patient and expect it to not work first time around! I got impatient and pee'd off so kinda stopped and will have another crack when Im really keen!

I will find the link to a site with a great DIY on shaving a MK3 front bar, he makes it look and seem too damn simple

[Preen59]

Well if you want to be tight fisted..

From what i've been told by a guy that's done a bit.. Melt the plastic on the bumper and smell it.. Find another piece of plastic to use as a filler rod that smells the same or very similar when you melt it.

Then you just melt the two edges and push the filler rod in and melt it as you go to bond the two parent materials together.

Easy.. :S haha.


There you go. I was helpful and everything.

[madglf3]

You guys should ask rayray the DIY KING, he did his didn't he?

[Mrk_Mickey]

You guys should ask rayray the DIY KING, he did his didn't he?

Yeah he did, there's a writeup on his blog I think! If he comes online tonight I'm sure he'll see this and (shout for joy...) post the link

Well if you want to be tight fisted..

From what i've been told by a guy that's done a bit.. Melt the plastic on the bumper and smell it.. Find another piece of plastic to use as a filler rod that smells the same or very similar when you melt it.

Then you just melt the two edges and push the filler rod in and melt it as you go to bond the two parent materials together.

Easy.. :S haha.


There you go. I was helpful and everything.

Bahaha...sounds just like normal welding! Easy! (Wait...I need to know how to do THAT first )

Yeah I'd love to do some more shaving on my car...it'd be nice to learn how to do properly, too!

[rayray086]

From what i've been told by a guy that's done a bit.. Melt the plastic on the bumper and smell it.. Find another piece of plastic to use as a filler rod that smells the same or very similar when you melt it.

Yep, sounds hicky but that's one of the most important part of plastic welding. Gotta use the same material that you're welding into! A rear bumper for scraps will do well. For DIY plastic welding, it's best just to use it as a way of keeping the panel in position so you can fix the rest of it on permanently without it shifting. Plastic products are created under pressure and certain temperatures so there's no way you can get the same kind of strength.

I just use a soldering iron with a flat-bladed tip. I get decent results by tacking weld points about an inch away from each other so it holds on nicely. I then join the "tack welds" by applying pressure and running the tip right in the middle, going slow enough so it melts it together. Do this all the way around the panel on the front side.

Next is just use a good epoxy bond or fibreglass and work it over the rear. Remember to scuff up the surface for better bonding. Try not to leave any air bubbles/gaps - hot air expands and it could potentially be easier for the bumper to crack later on.

Once that's fixed in place, use plastic filler (I use UPOL's PlastX which I got from VG Autos, pretty much across the road from Seb's workshop) to clean up the front. Plastic filler flexes a lot more than regular filler so it should reduce the chances of it cracking when you move the bumper around. Again, make sure the surface is very well scuffed and cleaned for maximal adhesion.

The bumper I first did was plastic welded the entire way around without any rear reinforcement, with just plastic filler on the front. The bumper's now cracked around the plastic welded part cos it had rubbed against the fence (I fail at driving) and same goes with the rear exhaust cut-out delete as well.

So yeah, just make sure the surface is very well scuffed and thoroughly cleaned before you lay on the epoxy and fillers. It'll help a great deal.

For pic references, search "Joey Russo" in the Mk3 section of the Vortex. You should find a pretty recent topic on a DIY on plastic welding.

[Golf Houso]

Thank you very much for the input guys, some valulable tips there. I've gotten a sheet of a very similar plastic which has a slightly lower melting point than the ABS, which isn't that great but is still ok to work with. I'll start practicing on some offcuts before I attack the bumper

Oh and I've busted my VR lip already, I might have a go at trying to fix that first

[rayray086]

Our front bumpers are PP+EPDM! The grille slats, lower duct pieces and side mirrors are ABS though.

It's not a case of similar melting point either... they may mix around once melted but they might not actually bond together well enough once they reach back to room temperature again! It's all chemistry though.

[DubSteve]

So in turn use front bars on front bars and rears on rears?

[Lorenz]

Rear bars and front bars should be the same plastic, thats what me and Ray have been using

[Mrk_Mickey]

So in turn use front bars on front bars and rears on rears?

rears and fronts are fine to use together, it's just the lips/trim (textured) and the front bar accessories like the grilles and stuff that are different materials.