Gluing Styrofoam For Carving

use gorilla glue and just don't apply it close to where you plan to sand. It is foam so it sands as easy as the foam.

 

I use urethane foam. Mix it and try to spread a thin layer evenly between the two pieces and then apply weight.

 

Rough up both pieces apply plaster of paris put them together and lay weight on top, when dry you can cut thru easy and its plenty strong.

 

I'm not sure which glue (or solvent) you use matters all that much because whatever is used will not sand the same as the adjacent foam. But, keeping it away from the "seam" is one okay solution. Assuming you're not using the pieced form for a thin skinned (coldwater) specie as this will be difficult to hide. You can fill it with some mache' also where things are sanded to sort've get the same effect as plaster mentioned above but without hitting the whole form. But, this too will sand slightly differently than the foam but you can blend it out before sanding to help hide. Easiest solution is to buy bigger foam! OR, at least make sure the foam seam is away from the show side.

 

3M Super 77 spray adhesive.

 

The best way I have found is to use the spray foam in a can but there is a trick to it. Lay the two pieces you are gluing side by side and mist one of the blocks with water. Apply the can foam (the type for weather sealing) in a zig zag fashion. Use a piece of cardboard to trowel it around and get everything coated. Then place the two pieces together. The water on the one side will activate the foam and allow it to cure overnight. Use ratchet straps or place some heavy weights on top to keep the joint tight.
The next day you will have a paper thin glue joint that is lighter density than your foam and won't cause the problems that gorilla glue or other things do. It will not come apart.

 

That can stuff works great as fish M said
But when you pull the trigger you better go with the rest on something else
As this is air activated
Now i use two part foam in the same manner
2 lb density for this application

 

The two part foam works well for me. One thing I do is spread it trying to cover all the foam(I use this for 7'+ gar so I have large pieces). I actually let it kick somewhat until it is getting tacky. Then fit the pieces together and work them back and forth to push the foam as even as possible. Then I weight it down. If I put the two pieces together while it is still "raw" it tends to push up in spots and make bulges. It's economical, easy and the seams are relatively simple to carve. As Clew said...2# works best for me and goes a long way. Good luck!!!!

 

If you immediately unscrew and soak the tip and clean out the nozzle end of the can you can save it for another day. I like the can foam as it's a lighter density and doesn't leave a hard line to deal with.