1" ridgid foam board

Loctite PL 300 Foam Board Adhesive.  It doesn't melt the foam yet it bonds very tightly.

It's a good gap filler as well.

It comes in a caulking style tube.

Mike

I glue it to the plywood with liquid nails and fill the seams with plain old acrylic caulk.
Ive used the foam board adhesive (PL300, etc) and it’s fine too, the caulk is just easier to deal with (sanding, carving and painting).
You can also fix everything in place with the canned spray foam, but then you’ll have to do a bit of trimming when it dries.

@pphegena posted:

Hi

I have decided to use the 1" ridgid foam board over the plywood table, there be 3 sheets of the pink board what do you use between the seams wallboard compound or some type of glue ? then i will put the roadbed on top of the foam board.

Regards

Prentice

ultra light spackle , is very light weight , has the consistency of frosting.  works great with  high density foam .  I think its latex based, smooth's out with a little water, cleans up with a little soap and water, can be allied with a putty knife spatulas, brushes and your fingers. I havent used plaster , Sculpta mold ,  or any other cements since the 1980's  when I started using extruded foam back in the 80's

I did not fill my seams.  Maybe I should have.  When it comes time to scenic, I put down a wide strip of painters tape.

Then I paint the foam brown or green.  Then sprinkle on my ground cover.  Then glue on top of that. 

The tape has never come up or separated.

Ron

A little vinyl caulking compound and then duct tape over the seam. I paint the surface a latex earth brown color and then sprinkle with WS fine green and yellow turf while still wet and the seam/tape disappears.