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I want to glue together several sheets of polystyrene (just a prototype / research project). I choose extruded polystyrene for its extra strength compared to expanded.

However, I am not sure sure which glue would make a better job at gluing. Since the surface to cover will be quite big, I prefer a cheaper glue, but still good.

I expect the final structure to be as light as possible, so I assume that cements are out of question. Also, the curing time should not be too quick, I might not be able to move so fast.

Note: I might embed meshes of glass fiber into the glue, for reinforcement.

Since I am not in the US, please provide me with:

  • generic description of the glue;

or

  • international brands of glue.

To estimate the volume of glue needed, do you think that the thickness of the glue is very important? Unless it is too thin, of course.

Any other hints / advice are highly appreciated.


I searched on the internet, and:

  • the descriptions were too generic, so I still do no know what to buy;
  • the brands were totally unknown to me.
  • Can you provide an example of how the end product is to be used? Different adhesives or alternatives may depend on whether your combine sheets are holding weight, or expecting shear force vs. compression force, or whether they'll be carrying any weight at all. – user24 Nov 22 '19 at 17:26
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Polystyrene is attacked by many organic solvents, so I'd rule out all solvent-based glues you haven't personally tested. Different compositions can be sold under the same name in different countries, or can change over time, and very similar names can have different ingredients.

That leaves you with two options; I recommend the second:

Water-based glues: These will give you a low-strength bond on polystyrene, but if you have a large area of a fairly weak material that might not matter. PVA (white craft glue, wood glue) would be one type, latex (e.g. Copydex brand) would be another, but you'd need to be sure you were getting a water-based product (many other glues with latex/rubber in the name are solvent-based). You'd need to use a thin layer, and drying times would be longer than expected, because you're relying on water evaporating and it has to escape.

Hot glue: Cool melt hot glue is plastic, which is melted and applied to one surface. This sticks well to polystyrene. It cools and solidifies fairly quickly when exposed to air, but extruded polystyrene will keep the heat in, so setting times will be increased. As with water-based glues you'll have to support the workpiece while the glue dries. This should give a stronger bond, as it is better able to fill the gaps in the surfaces. You can get a range of colours, but don't expect to colour-match. With decent pressure as the joint sets you can avoid gluing right to the edge; with a suitable colour the join can be subtle.

  • Actually solvent based glues are used on plastics for that very reason, in melts the plastic and forms a weld, much stronger than conventional adhesives. Water based glues are unlikely to work because it will not bond with the plastic – rebusB Nov 23 '19 at 17:56
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    @rebusB, extruded polystyrene is a form of polystyrene foam. The problem with solvent based adhesives on polystyrene foam is that the foam is almost all air. The solvent quickly makes the surface disappear, so you are gluing a hole. – fixer1234 Nov 23 '19 at 19:06
  • re: water-based glues, there are some that are more tacky, like Aleene's Tacky Glue, that will grip polystyrene foam better than plain PVA craft glue. – fixer1234 Nov 23 '19 at 19:18
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Adhesives that bond well to polystyrene include:

  • Cyanoacrylates – Cyanoacrylates bond well to polystyrene. Use only enough adhesive to cover the joint, then assemble as soon as practical. For best appearance use a low odor grade.

  • Two component epoxies bond well to polystyrene.

  • UV Curable – UV Curable adhesives are an excellent choice for bonding polystyrene.

(Lifted from Permabond website and edited to remove product references.)

I would probably go with a two component epoxy. They are widely available and have a longer working time than the water like Cyanoacrylates. However the Cyanoacrylates may give you a cleaner and lighter weld.

Another advantage to the two part epoxy is that you can embed stuff in it. I do not think you would need to do that to make a stronger bond though as having another material in there may actually weaken the attachment.

Just check the product labels to be sure it will work with the specific materials you are using, and doing a test on some expendable material is always a good idea.

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For simplicity, I'll refer to all polystyrene foam, both extruded and expanded, as "Styrofoam"; the adhesives will be the same. There are a lot of adhesives that will stick Styrofoam together. Most of those will be adequate for an art project where nothing will be under stress. If the glue joint needs to have mechanical strength similar to the Styrofoam, itself, (i.e., you need to "weld" the pieces together to have strength similar to having originally molded a single piece), only some of the adhesives will do that.

The joint strength will be affected by several things:

  • The surface area of the joint. If there is a lot of surface area, even an inexpensive, weak glue, like PVA craft glue, will have a lot of holding strength if you give it time to dry.
  • Drying time. For adhesives that cure by evaporation, a large surface area can take a very long time for the glue to cure. The glue joint is sealed in an air-tight "container" between the pieces, and evaporation happens at the exposed edge after migrating through the glue. It can take a week or longer for the glue joint to have real strength. You will have a strong joint only if you have the time to wait.
  • Surface texture. Some Styrofoam has a very smooth surface and some has a lot of surface texture. If there is significant surface texture, only the high points will be in contact; so it might be a large area, but not much of it is actually touching. OTOH, surface texture provides more surface for the adhesive to grab. That difference affects the type of adhesive that will work best.

    For example, regular cyanoacrylates (super glue, the thin stuff), has the most strength as a microscopic layer between two tightly-mating surfaces. Globs of it filling voids doesn't have great strength. That will work on Styrofoam with a very smooth surface. On a textured surface, it will be an expensive adhesive that doesn't buy you much over something like PVA glue that fills the voids and has adequate time to cure.

Before getting to specific recommendations, I'll preserve here something I mentioned in a comment. If a water-based glue, like PVA craft glue, will be adequate for your needs (and you have time for it to cure), tacky glue, like Aleene's Tacky Glue, will hold better than plain PVA craft glue.

There are several adhesives that haven't been mentioned yet, that are the strongest if you need a "structural" joint. These will create joints that are stronger than the Styrofoam, itself (if you try to separate the pieces, the Styrofoam will break in another spot before the glue joint separates).
There's an interesting test of adhesives joining Styrofoam in this YouTube video. I found the results surprising. Note, though, that the tests were performed after 48 hours. A number of products failed because they hadn't cured yet. They may well have fared better if given sufficient time:

  • Glidden Gripper Primer and Sealer. This is one I wouldn't have thought of, but it is apparently a well-known secret among crafters. It's inexpensive compared to many of the adhesives, and basically welds Styrofoam together. In the side-by-side test I linked to above, it came out the best.
  • Gorilla Glue. It requires moisture for the glue to work. On large Styrofoam surfaces, curing time can be long if you rely on room humidity to seep into the joint. Mist one of the surfaces slightly before gluing to speed things up. If you need to avoid the glue expanding out of the joint, there's a non-foaming version. Otherwise, just apply it sparingly and not too close to the edge, and wipe any that oozes out before it hardens.
  • Great Stuff (and similar) foam sealant. Use a tiny amount because it expands -- a few dots or a thin bead -- and press the parts together before it starts to harden. It may expand out the sides of the joint, so there can be some cleanup if you use too much. Wipe off excess while it's still liquid.

There are a number of other adhesives commonly used, including construction adhesive designed for the purpose and spray adhesive, but they aren't as strong as these three.

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