What does Weld-On 4 NOT stick to?

I need to glue two pieces of acrylic edge to edge. I have Weld-On 4. My question is what do I set the pieces on, while gluing, so that the glued parts aren’t also glued to the surface?

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I generally prop and clamp the bonded areas so they aren’t touching anything. I have, however, used concrete pavers and aluminum foil. A key thing would be to not leave the piece sitting in a pool of Weld-On.

To clarify for your use case: put a piece of something (cardboard, Dradtboard) under each side of the butt join with the joint itself suspended in space between them.

For one project, I cut a slot in a single piece of Draftboard to do that, clamping each side of the joint to the board to hold it with pressure.


I use the lid of my GF to assemble most projects, including those cut from acrylic and using w/Weld-On. I just scrape it down with a sharp razor blade when it starts to get cruddy. Right now you can barely see thru it with all the wood glue that’s on it!

If you are paranoid, however, you could always used the crumb tray.


I’ve done that with wood glue. Maybe I’ll grab a piece of glass and try that. Thanks!

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Unfortunately, the pieces are too small to support that way. I should have mentioned that. That’s good info for larger pieces though.


If they are really small, you might have an issue getting them off the glass without breaking them apart. You only need the smallest drop of the solvent.

Note that laser-cut edges are not straight. There is a taper from top-to-bottom, so for joining parts, as with inlay, it’s often best to flip one part relative to the other.


I just set these on a concrete paver and applied the Weld-On with a needle applicator:

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I use a silicone mat I have for soldering. Nothing sticks to those. You can also bake cookies on them :grin:
There are also ones for “crafting” that should also work well.

Soldering Mat Heat Resistant 932°F Magnetic Silicone Electronic Repair Mat for Cellphone, Laptop, Computer, Heat Insulation Pad for Soldering Iron Station15.9” x 12” (Grey) https://www.amazon.com/dp/B075M7PQZX/ref=cm_sw_r_cp_api_fabc_XejUFbYDMJ0NN


Oh, now THERE’s a thought!

I have some of those BBQ cooking mats - I bought as a liner for the bottom of my countertop oven.

Now if I can find the unused ones…

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I have found that there is one thing that will in fact stick to silicone mats and that is CA (cyanoacrylate) glues. I ruined a couple of different silicone mats and molds that way.

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Holy Guacamole, that is awesome on more than one level

CA Glue won’t stick to wax paper. Found this out by happy accident.


Absolutely nothing sticks to UHMW tape, including the solvent glues. (Tested with SciGrip/WeldOn 16). They will peel right off when dry.

You can lay a strip of that down underneath the seam and reuse it over and over again. (Which is good since it ain’t cheap.) :slightly_smiling_face:


Glass is ideal–though I’ve not tried using the lid as @eflyguy has, but I had a piece meant for use in a picture frame that came in quite useful to put on my work bench when using the Weld-On 4.

For trying to clamp together pieces, maybe have some small pieces of glass cut to use between the piece being welded and the clamp/brace?

Though glazed tiles may work, too since the fired glazes on many tiles is very similar to glass. And pieces of those maybe easier to work with than glass!


I use Acetone to join Acrylic. It’s a true solvent, no actual adhesive. Surfaces mated together melt and merge and the Acetone evaporates and I’m left with a joint that’s generally as strong as the surrounding plastic. To join at right angles, I’ve got a set of adjustable-angle corner clamps. Set 'em at 90º, clamp the pieces making sure the seam I’m going to bond is straight and gapless, then I hold it so the seam is vertical and I get a drop of Acetone and run it down the inside angle of the seam. If it’s a long seam, I might drip another drop or two further down the seam. Wait 10 minutes, remove clamps, parts bonded. Since I’m not clamping the parts to anything except themselves, there’s no worry about them sticking to anything. But the Acetone isn’t glue, so unless I go nuts with it there’s nothing for anything foreign to stick to.

I’ve tried to break Acetone joined pieces and often times the break occurs someplace adjacent to the seam, the seam itself doesn’t fail.

My wife’s nail polish remover can be used in a pinch, but “industrial” is best. And the stuff is cheap.


That’s another good idea. I already have some glazed white tiles.

I will have to remember this for that future. Unfortunately, I’ve already purchased the Weld-On.

if you have the same experience as me, it’ll evaporate out of the can before you need it again :slight_smile:

Someone recommended drilling the tiniest hole in the inner cap vs removing it and then using a squeeze bottle needle applicator to get it out of the can and apply it with the least possibility of future evaporation.

Acetone I always have around for cleaning metal projects I work on and that doesn’t seem to evaporate out of its container.


Need a disclaimer with this stuff.
It became popular to have around with 3D printing, for smoothing prints and cleanups.

It is liquid napalm that gasses a flammable vapor.

Safe to use, as long as you have no open flames around and use it sparingly.

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I have used it on tin foil, and it doesn’t seem to stick to that.