What do I use to glue plastic that's safe for the inside of a hot car?
July 4, 2015 3:47 PM   Subscribe

I have a bunch of Lego Minifigures in the back window of my car. I live in Los Angeles, and when my car gets too hot, the plastic in the Legos expands and everything starts coming apart. I want to glue each figure together so I'm not constantly having to reassemble them, but I don't want glue that would give off harmful fumes when in those hot car conditions. I've tried basic craft glue so far, but it doesn't seem to last very well in the heat. Any thoughts? Thanks!
posted by dithmer to Sports, Hobbies, & Recreation (10 answers total) 2 users marked this as a favorite
I think LEGO have used MEK (Butanone) and gamma-Butyrolactone, which are solvents that basically melt the parts together at the surface.

So generally, you want a solvent-based ABS glue. Most solvents won't give off further fumes after drying is complete - any residual chemicals are extremely volatile and will most likely evaporate into the open air within a few hours.
posted by pipeski at 4:03 PM on July 4, 2015

Sugru. It is magical.
posted by Maarika at 4:12 PM on July 4, 2015 [1 favorite]

2-part epoxy would probably work. It will emit some smelly chemicals for a few days, but I would just open the windows.
posted by H21 at 4:20 PM on July 4, 2015

Solvent type glues work pretty well, such as old fashioned model airplane type stuff. PVC pipe glue works pretty well, too. Cyanoacrylates (Crazy glue) also work well.

Solvent glues "dry" by the volatiles evaporating. Once dry, it'll take a lot of heat to make them give off fumes. Similarly, cyanoacrylates, once cured.

Other things might work pretty well, too, such as silicone, rubber cements, polyurethanes, pretty much anything that will work with rigid materials and plastics. But the solvent glues and Crazy glues are probably easiest and cheapest, and common.
posted by 2N2222 at 4:26 PM on July 4, 2015

Maybe the glue they sell to glue your rearview mirror back on?
posted by luckynerd at 5:05 PM on July 4, 2015 [2 favorites]

If you don't like the weird solvents, you could use aquarium caulk, which is silicone and uses acetic acid as the curing agent. Its melting point is effectively it's burning point, so it's no danger of coming apart. It will, however, tear and is goopy to work with.
posted by plinth at 5:41 PM on July 4, 2015

I'd second pipeski's recommendation of using a solvent, like MEK or even acetone to melt the pieces together but for one caveat- they will affect the appearance of the figures if you're not careful (i.e. they can make the shininess go away if they run.) For attaching lego pieces maybe set the bottom piece in a very shallow bath of the stuff, just enough to cover the raised pips or whatever those round dots are called, for several seconds to a few minutes, then remove and push the upper piece on carefully. Test this out with some scrap lego.

Cyanoacrylate (super) glue might also work, but I wouldn't recommend using the home versions, they're all very brittle when dry and might not do well when the pieces start expanding with the heat. If you go to a local hobby shop they have formulations that have rubbery versions of the stuff, which I imagine would be better suited for this. There's also an instant hardening spray available at the same shops, usually right next to the glue. You put the glue on one piece, spray the other, join, and it's pretty much done at that point. I say this because another disadvantage of working with CA glue is the fumes will cause a whitish powdery coating on whatever you're trying to glue wherever there are any organic oils or whatever (read: fingerprints) present. The advantage to using the spray is that the fumes seem to dissipate MUCH faster. Again test on spares to be sure it will work like you want.
posted by mcrandello at 7:29 PM on July 4, 2015

I would recommend Weldbond glue. I've used it many times for various projects and it's amazing. Similar strength to super glue but does not bond instantly. Non toxic, no fumes.
posted by Lay Off The Books at 7:36 PM on July 4, 2015

MEK is definitely the answer, I've been repairing cracked or broken Legos for years with it.
Nasty stuff though, be careful with it.
posted by Confess, Fletch at 10:20 PM on July 4, 2015

The answers here are split between glues and cements/solvents, and I think it's useful to understand the difference:

Glues bond to the surface of the two materials. Glues are awesome for porus materials, or other places where the surface has enough texture that the glue can infiltrate and physically grab on to the material. Sometimes the glue is stronger than the original material (wood glues are often stronger than the adjoining materials), sometimes it's weaker, but it's always limited by the adhesion of the glue to the surface.

Plastics are usually very smooth, so glues don't generally work well on them (although some glues have solvents in them that work as cements, but...):

Cements and solvents become the material. With plastics like you're working with, if the surfaces are clean, the solvent melts the plastic, then evaporates away, leaving you with a solid piece of plastic in the middle. This is a weld, the material is now continuous.

Lego appears to be an ABS plastic. If you go to your local hobby shop and get the brush-on liquid cement for ABS or dual plastics (they've generally got one just for styrene, and then one for styrene, ABS and other), which will probably be MEK or GBL or something else involving chloroform, on a clean surface that'll give you a joint as strong as the original.
posted by straw at 10:19 AM on July 5, 2015 [3 favorites]

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