Weld-on #3, 4, 16 also work well for solvent welding of PLA. Main ingredient in them is Methylene Chloride aka Dichloromethane aka DCM and it works for solvent welding a variety of polymeric material including PETG.
DCM is being widely banned in consumer products (e.g. Paint Strippers) due to health concerns and I think Weld-On is not listing the Acrylic glue line-up anymore.
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Just bought some of the Weld-On 16 in a tube from Amazon, and I’m pleased to announce that it indeed welds together PETG. It qualifies in my book as worthy for the job. I don’t think I will be able to pull it apart without breaking one of the pieces, and that’s my standard. However, it did not work on the PLA (not for me anyhow). Warning to anyone who gets a tube of this: When you remove the cap and tilt the tube, the stuff will come running out, not what I expected in a tubed-product. So just be ready. Yep, I wouldn’t be surprised if it gets banned. Just about anything that works gets banned.
As @JonRaymond and @Josh-3D can confirm, the stuff has a tendency to stick the wrong things. Fast and non-discriminant, made all the harder if your wife is overseas calling you and the dogs are getting excited as she was on speakerphone 
Acetone assists in dissolving CA enough for separation, and should be automatically added to your amazon cart.
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The link I put above from @Olias referenced some plastic cement that works with PLA
Maybe I missed it, but why not 3D Gloop for PLA. Use it all the time. Welds the parts.
I use “MEK”, which is a solvent. Works for many, many plastics. Not sure if it’s “universal” but it’s close. The wetted plastic parts melt together and the solvent evaporates and the parts become one.
Can also be used to smooth PLA prints. But it’s kind of nasty stuff (like, you don’t want to be breathing it very much), I only use it in small amounts in well ventilated areas.
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Everything I’ve read about it says that the shelf like is like a hot minute. But, you’re right, I never took the chance to order it based on that. I got the impression that you’d better use it all in a day or so.
Thanks, I’ll put that on my list of things to try.
I have had it last abouty 3 months or so. I order when I know I’ll need a bit of it. Keep the lid tight and should be fine for a bit.
I use solvents, acetone, MEK or Amyl acetate. Some additives in pla allow any of them to work. Acetone evapourates quickly, MEK not so fast, Amyl Acetate is used in food flavourings, and is a bit safer than the others. You can get them all from Amazon, at around a tenner a litre, and get some blunt needled syringes to apply. If you smooth the mating surfaces, apply a drop of solvent at the join, it will wick in.
My son and I have had good results with 2P-10 from Amazon.
Some very nasty chemicals in it. Their own website has a very prominent safety disclaimer that tells you “gloopis not for everyone” and they will offer a refund if you feel unsafe using it. That’s business speak for “this stuff might make you feel sick”. I don’t think i’ve seen such language on other glues.
I haven’t had a problem gluing PLA once I realised how dry it was and used accelerant. However I have had some types of glue and paint not stick to PET. I had to paint drink bottles once, and it was not a pleasant experence (a bottle is about the right size to make scale models of chemical tanks).
Another thing you can use for superglue (CA) accelerant is baking soda. The glue will stick to that, and it will stick to the model.
Solvents and glue work very differently.
If you have the option, solvents will generally result in a stronger bond.
But solvents tend to be chemicals that are nasty to work with.
For ABS I use plain old Acetone. Works as well as any of the more “hard core” solvent options. But there are plenty of plastics Acetone won’t act on, or won’t act on very strongly, where something like MEK will.
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Did you try any of the various “plastic adhesion promotors”? I’m going to be filler priming and painting various prints made from different filament types. I’ve never done it before, so this is entirely seat-of-the-paints. Anyway, since the primer filler and topcoat are both SprayMax 2K, I decided to maybe improve the bonding by spraying on some SpraMax Plastic Adhesion Promotor (which is only 1K, but from a cursory survey it seems like pretty much all such products are 1K) and crossing my fingers in hopes that everything will stick well enough that I’ll never have to re-do it in the future.
I’ve already ordered the shaker cans, so I’ll know for certain one way or the other after they arrive in about 10 days.
SpannMagoo is correct with the 3dgloop. If your talking about welding acrylic together this is basically the same thing with pla. You’ll break other layer lines before you break the 3d gloop attachment point. They are a smaller company so sometimes they’ll be sold out but justs wait a week and they’ll be restocked.
I sprayed it with spray putty, it was fine after that.
(Vallejo and Citadel paint sprays weren’t sticking)
Acetone is great for dissolving cyanoacrylate glues but people ought to be as careful as possible to not get glue on fingers to where they need acetone. The reason is acetone messes with lipids in the skin and helps other chemicals cross the skin barrier. In other words it can help transport cyanoacrylate glue into the body.
It’s not a huge effect apparently, and cyanoacrylate glues are used in surgery now, but still something to be careful about.
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