how do you fasten 2 2" x 4" sheets of foam board together? (not on top of each other-I mean end to end, to have a surface that’s 4’ x 4’) I tried Elmers wood glue, but it didn’t work.
Also, how do you fasten it to plywood?
I would only fasten it to the plywood. Lay them along side each other over a sheet of plywood, and use a latex caulk or PL300 to glue them to the plywood. There is no need to glue the foam sheets to each other if you glue them to the plywood.
Now, a question to muddy the water: why glue a foam of 2" thickness to plywood at all? It is plenty strong by itself. Save yourself the expense of plywood.
If you must glue the ends or sides of the foam to make one sheet, I would press bamboo bar-b-que skewers along the edge of one piece of foam, and then shove the ends together hoping that the skewers provide a form of reinforcement…like rebar. Also use the glue, of course.
If you make a benchwork that provides support under the 2" foam at regular intervals, you don’t need to have plywood, nor would you need the skewers, just a few dabs of the glue to keep them from spreading or sliding.
My [2c]
How long did you let the wood glue dry? I have glued foam together with it successfully, but keep in mind, foam doesn’t let air through so glue will take a LONG time to dry. I let mine sit for a week and the bond is now very strong.
ok, that must be it, cause I only let it dry for a couple hours.
I read a forum recently, that addresses the end to end gluing off foam sheets. Create overlapping ends with a razor knife. Cutting the width horizontally into the end of the sheets, one on the top half, the other on the bottom half, so that when they are joined together, they interlock. Sort of like a couple of pieces of tongue-and-groove wood, only with the end of one sheet overlapping the other, instead of a groove. I use Liquid Nails for Projects to glue all foam. It dries a lot quicker than white glue.
I tried to make all the end to end joints fall over a layout support member. Where that wasn’t possible I added a strip of foam under the joint. I used yellow carpenters glue and it works fine.
Nick