Foam insulation board

Foam is pretty brittle stuff. Unless you make it quite thick, it will be easily susceptible to breakage. It's also easily dented. If you're putting it on a shelf, I would recommend that it be at least 2" thick at the narrowest point and have a fascia made of foamcore or very thin MDF. Even then, I would be very concerned. Once the layout warps, it's all over.

If you're mostly concerned about making benchwork because you don't have the tools, consider buying prestretched studio canvases with 1 1/2" stretcher bars and removing the canvas. Add some precut MDF from the hardware store, and all you need for rigid benchwork is a screwdriver. Another option is buying cradled panels from the art supply store. Your size options will be more limited than surfacing it yourself, but it's done all in one go. A 36x48 inch panel will run you around 70 dollars, and you will have saved significant labour time on benchwork.

I have every intention on building the benchwork for my new layout almost completely with foam - less a 1x2 frame on 16" centres (exactly like moose suggested - wisdom he's shared in a few similar threads)  and then sheathed with 1" foam - LAMIATED.  I will add screw blocks for fascia etc.

Kashirigi's suggestion on using painting stretchers is really clever.  I wouldn't be prepared to rip apart a gallery style canvas just for the wood, but art stores do sell the loose stretchers in 2" incremental lengths.

I didn't know that foam will warp.  I recently built a large rock out of several layers of the stuff for a film I did.  It had to support a 6 foot 7inch tall, 180 pound man and the stuff held up very well for several days and takes.  This is why I figured that if I built it up about 6 inches and placed it onto shelving brackets it could hold up quite well.  I'm also very shaky with wooden bench work so this was my way of avoiding that.  The layout will be approx. 7 feet by 2 feet and at about eye level from the floor. 

I have to agree with Moose though that rooms in apartments do tend to be poorly assembled.  I'll have to take that into consideration.

-Joe 

I was thinking about this thread while buying 'my' foam this evening and I came across a few things that might help.  The discussion has largely focused on how to adequetly support the foam in fear of it sagging.  In the insulation section they sell firring strips (C channel) intended to be set into grooves on the 2" thick pink stuff, however you could slip these strips around the sides of some 1.5" thick foam to create a very rigid edge that would undoubtedly handle any stresses placed on the foam.  Likewise, the drywall section has similar 2" C-channels intended for windows that could also work. 

Much like the j-moulding used on drywall. 

If it's laminated to 6" thick ()and sitting on shelf brackets I'm going all but guarantee it won't sag.  I'm not speaking from experience within the hobby - this is experience gained building/renovating houses.  I think you will have more then adequate support!

As for the firring strips I mentioned, I was imagining that these would allow for thinner benchwork with no fear of sagging.

Heck, I think 4" would be plenty strong - with shelf brackets every 12", rock solid.

Michael
www.modelrailroader.ca

Chances are, your wall studs will be 16" on center, so that will be the spacing of your brackets.   But at 3 layers of 2" (I'd even second the 2 layer opinion), it should be more than adequate, as long as the layers are truly laminated...in other words adhesive bonding all or nearly all of the mating surfaces...spot gluing will not be nearly as strong.  

A while back I played with the idea of building a 42"x76" semi-portable table top layout entirely out of 2" foam.   At that size, with one uncut slab of foam as a base, and a 2nd layer cut for a river and an underpass, it was almost strong enough.  That combination, with my track pinned down and a few tools on it for simulate weight, only sagged slightly over the 76" span, when lifted from the ends...not enough that it was in danger of breaking, but enough to cause scenery and track problems.  I suspect that a 2nd uncut slab of 2" foam properly laminated, with a 1X perimeter glued around the edges, would have been sufficient.  Since height was an issue for me, I opted for a hollow core door, with 2" of cut-into foam on top, instead of adding another layer.