If you use the spray foam as I described, dowels aren't going to help much. If your diorame is going to be wider, (longer?), than 6 feet, I would recomend at least a 1x2 frame for structural strength, or two layers of foam overlapping the joint.
Jay
C-415 Build: https://imageshack.com/a/tShC/1
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Thanks everyone for the advice. Would dowel rods inserted in be ok as well for strenght and holding together?
alco's forever!!!!! Majoring in HO scale Minorig in O scale:)
Use Spray Insulation foam that comes in a can like Great Stuff. It's the best foam "glue" there is. I think Gorilla glue will also work, it's essensially a similar formula, just doesn't expand as much.
Apply the spray foam to one edge, then press the second piece to it, maintaining the pressure until the foam has set (6-12 hours). The joint will be as strong as the foam itself.
To keep the two sections together while the "glue" sets up, use some 3" coarse sheetrock screws to "clamp" them together, (you can remove them later). You should also secure the sheets somehow (weights or screws) to keep them flat.Trim the ooze from the joint with a knife after the foam has cured.
If you are attaching the foam to a wood frame, you can use the spray foam to glue the first sheet and "calmp" it to the frame, (run a bead around the frame), then add the spray foam to the joint and the rest of the frame, add the second sheet and screw it down. All the screws can be removed the next day and you'll end up with one solid monolith.
A couple of cautions when using spray foam: IT STICKS TO EVERYTHING! Wear gloves and use eye protection. Put some polyethelene plastic under your work area. Acetone works somewhat to remove the wet foam from skin or clothing, but for the most part you'll have to let it wear off.
We used a lot of spray foam (in 50 gallon drums) at Dunham Studios to build up rock strata because it's hard much faster and easier to carve than any of the so called traditional methods. We painted on thinned lightweight plaster after carving to close up all the air pockets and finished with textured paint and washes. The industrial foam we used cured hard in 20 minutes, so we would spray an area before lunch and be able to carve it after we finished eating. Too bad the canned stuff isn't that fast.
I don't know the sizes of the pieces you're trying to put together so I'll just give you an idea.
Mortise and tenon might work. If they are say 8' long and 30" wide and you want to make it 8' long and 60" wide and you don't want plywood on the bottom. You need a table saw, a piece of 1/4" plywood 3" wide and 8' long and some carpenter's glue friendly to foam. Set the rip fence of your table saw 1" away from the outside of your blade. Set your blade height 1 -9/16. Run the foam through standing on the factory edge for the 8' length, do both pieces. Move your rip fence in 1/8" toward the blade, run the 2 pieces through again, same cut. You should now have a channel on the edge of 1/4" wide and 1-9/16" deep on the 2 pieces. Simply apply glue liberally in the groves, insert the plywood in one grove, apply glue to the foam face of the edge and align the other piece with the plywood and compress together wipe off excess glue with a damp cloth. Maybe stand it on edge against a wall and add some weight on the top edge, let set for a day or 2 and I would say it will hold with no problem.
PL - 300
Use a scarf joint or a lap joint, not a butt joint and you'll be OK.
The mind is like a parachute. It works better when it's open. www.stremy.net
That will work. You could also use masonite.
Ron K.
hmm well that won't work. I have odd pieces left over from a construction project here at the house so all I have is 2". I am thinking of laying a piece of thin wood underneith I guess to glue the foam to.
Mike
You will never get two pieces butted together to hold - too little area for the stresses. You would be better off using four peices of 3/4" doubled and staggered. You could also back up your 2" foam with 3/4" foam; again staggered so the joints don't overlap. I would recommend clear adhesive caulk for gluing the pieces together. Clamp or lay flat with heavy weights until dry (about 24 hours to be safe).
I have 2 pieces of 2" pink foam that I want to glue butted together. What is a good strong adhesive to use. Should I reinforce this joint with something. Planning a diaroma and 2 pieces butted together gives me the width I need..
Thanks for the help