Are there any recommendations out there regarding the “best” glue to use when joining slabs of polystyrene together? I picked up a can of 3M Super 77 thinking from past experience (not with foam however) that would be the best solution. Later that nite i found that 3M makes a spray glue specifically for foam so i made an exchange. I’m not sure if it’s an issue with the glue itself or the foam, but even after 2 days of dry time, the glue isn’t entirely set. The sections i glued up 12 hrs ago are still able to be moved around. Possibly epoxy (West System??) is the best solution, however will a hot wire cutter be able to cut through that once cured? Or, was the Super 77 my best bet?
I’m curious what you’ve all found to be the best.
I use Elmer’s White Glue.
Thin with water, roll on with 3 inch roller, allow to get tacky, press together.
I also have used the yellow carpenters glues - but find them to be hard when dry. Depending on the size of foam - you can also use dabs of hot-glue in areas that won’t be cut away. If you happen to glue on a cut-line the hot wire will cut through the glue too.
PS - I use stainless fishing leader wire, which will stretch if over-heated - but it’s so much cheaper than nichrome wire as well as being able to find it in sporting goods stores. You just need to heat to point of melting foam - doesn’t have to be red-hot. (for those thinking of trying it) I use an old electric toy train transformer for DC power as it has a regulator already built in for train speed which controls temperature of wire.
Yeah, i was looking for one of those model train transformers a year ago when i was making floats for an RC plane… couldn’t find one at the time and bought one of the commercially available ones at the local hobby store.
I’ll give the white glue a try though - thanks for the suggestion 
You can use a thin layer of epoxy and still hotwire through it OK. The trouble occurs when you have glassed over the foam and are filling and sanding. The “solid” line of expoxy does nor compress like the rest of the foam and you tend to sand through at that position, leaving a depression on the glue line. Need to sand soft and lightly!
It is best to use a flexable type glue. There are glues made specifically for gluing foam, but test them first as I have found one that did not set, but remained soft and tacky.
The latest glue I am using is a single mix (no hardener) polyurethane glue - “waterproof, bonds virtually any material, ideal for woodworking, boat builders quality, sandable and paintable”. The one I am using expands and foams over time - great for gap filling - and if allowed to fully set (24 hours) can be sanded etc. Be carefull as it is not water soluble, and sticks to skin quite well. Very successfull for foam, no trouble for hot wires.!
I found it in a hardware store (Aus) among the other wood glues. (About the same colour and flow as a thick honey.)
Jon
I use the polyurethane glue to glue together sheets of pink foam (or blue foam.) I use it on all kinds of wood projects too. You need to apply some pressure or weight to your pile of slabs, to keep the glue from pushing the slabs apart. You will see the glue seeping out of the seams as it expands and cures. Trim off any glue that seeps out after an hour or so when it starts getting hard; otherwise it’s a sticky mess.
Soaking the bottle in some warm water will help the glue flow better, if it’s too thick. And try not to suck air into the bottle; the moisture in the air will harden the glue in the bottle.
HTH
Ummm - wouldn’t expanding “foam” glues have a tendency to spread the layers apart? With hot glue “dabs” or white glue, there is no need to clamp or weigh down the pieces. Just a thought.
The polyurethane glues (like Gorilla glue or ProBond) are not “expanding foam” glues. They just foam up a little when they cure.
That’s why when you glue two or more slabs together you put some weight (a couple big books, coffee can with sand or whatever) can won them. The glue doesn’t expand as fast as you are suggesting. It expands into the pores ( especially good for wood joints) and makes an even tronger bond. You need some kind of pressure when gluing ANY kind of pieces, even with hot melt or white glue- especially with white glue, as it takes hours to harden and will slide easily without clamps. You need to have a tight joint to get strength, and that means you need pressure or weight.
Are you sure you’re not thinking about expanding foam insulation? People sometimes use it for loatation, and get a surprise when it ruptures the hull at the seams.
BTW- on a F/E website, one person insisted that “moisture-cure” glues would be fatal on a boat as the glue will dissolve when it gets wet- NOT. Once cured, it’s waterproof.
thx