Rigid foam over Sievers benchwork will be plenty of strength for HO. You may have trouble finding 2" foam down here. Lowes and HD only carry 3/4" so you will have to adhere a few sheets together to get the thickness you want.
My 'California Basement" (garage layout) is built out of 2" foam directly laid on 1x4" open-grid cross bracing and I've had no shrinkage problems in the 7 years it's been in existance. It's a fairly large 24x24' layout, and has a trackage elevation change from 0" at my main yard to 24" at the highest trackage point, and it's all foam. Lightweight and sturdy. No problems at all.
I use cross-bracing about every 18" or so on the gridwork to better support the foam, but as you layer the foam, you increase the rigidity a great deal. It's worked for me very well, especially since here in the Central Valley of California we can be subjected to some fairly drastic climactic changes during parts of the year.
Tom
Tom View my layout photos! http://s299.photobucket.com/albums/mm310/TWhite-014/Rio%20Grande%20Yuba%20River%20Sub One can NEVER have too many Articulateds!
My experience with cork has been uniformly negative, regarless of climate. It dried out in Northern Virginia and Eastern Maryland where there was no air conditioning, and it dried out in coastal Alaska (also very wet and humid). It generally took cork roadbed about a decade to dry to the point of crumbling when touched, but I had 3 separate cases bought decades apart do the same thing. My father had the same experience in the mountains of North Carolina (also very humid, with no air conditioning).
Since some others have not had my problems (others have had similar experiences) I have been trying to figure out what when wrong for me. In all 3 instances, the cork roadbed was fastened with nails or track spikes, not glue. In all 3 instances, I never got around to ballasting the track, either. In one instance, I handlaid track on the cork so there was some glue for the ties. In one instance, the cork went dry and crumbly in the original box.
My conclusions are that gluing cork roadbed to the foam or plywood, and gluing the ballast to the cork serves to partially or mostly seal the cork, substantially reducing the rate at which it dries out. I also suspect that many cork users actually have the drying occuring, but as long as they don't cut or try to work the cork, never know how dry it has gotten - remember it took a decade in my experience. Dried-out cork looks the same as fresh cork until it is disturbed.
In contrast, my handlaid track on unsealed Homasote never had any problems - despite moving from coastal Oregon (no A/C) to Gulf Coast Florida to East Coast Florida (no A/C) to Indiana basement over a period of 9 years. Of course, this track was ballasted so the top of the Homasote was pretty decently "sealed' by the glue for the ties and ballast. And the Homasote was glued to the 1/2" plywood ribbon subroadbed.
my thoughts and experiences, your choices
Fred W
Ten years ago I built a modular model of Sitka AK for the US Park Service. The construction of the 2x5' modules consisted of two pieces of 2"foam separate by 1x4 pine frame around the rim. The pine was screwed at the corners and the foam was glued using Liquid Nails for Foam . The modules have been on constant display for ten years with no detioration except for the normal bumps and grinds from moving them around. The whole 10x17 display is mounted on folding sawhorses purpose built. I got the Idea form an early 90s N-Scale mag. BILL
I use foam roadbed over a 2-inch foam base - no plywood. I'm in Massachusetts, and the layout is in a "living space" climate-controlled room. My layout's wood frame rafters are 16 inches apart, and I have no problems with sagging, as the foam is quite stiff.
Does anyone have any problems with cork roadbed in humid climates? I'm just throwing this out as a possibility, having no personal experience.
It takes an iron man to play with a toy iron horse.
With the 12 inch grid spacing under it, thick foam should be rigid enough. The only downside is that it doesn't give any way to securely mount anything to the underside. Since my switch point drives depend on screweyes for guides, I have a thin layer of plywood under the foam. It also provides something solid to screw risers to if you go for cookie-cut roadbed under multilevel track with connecting grades.
I have heard that foam alone is noisier than foam over plywood, but I cannot speak from personal experience in that area.
Chuck (Modeling Central Japan in September, 1964)
Thanks for the feedback. I do plan on using the cork roadbed. I've got to give some thought to groundthrows versus DCC controlled turnouts. My layout plan would certainly accomodate reaching for groundthrows no problem.
Tim Fahey
Musconetcong Branch of the Lehigh Valley RR
Just go with the foam and use latex caulk to adhere it. The benchwork you are using is much better than mine and I use the wrong foam and have not had a problem. Only problem you have with foam is if you lay track right on it is the turnout controls. I caulk cork roadbed down for the track which I caulk in place and I am using grownd throws.
I would at least use 1/4" plywood under the foam board. My reason is to give some rigity to the foam. Also if you want to add a lake or a river you are going to need something as a base for the bottom of the lake or stream bed. I do not know your layout room, but if some heavy should fall from a high shelf you can punch a hole in your layout. Just my opinion. Best of luck to you.
Thanks, I probably wasn't accurate enough in my original note. This will be a permanent layout. I'm just using the pre-built modular benchwork but it will be bolted together. Thanks for the feedback.
I don't see any problem. Many have built on 2" foam with only minimal framing successfully. Since you are doing modules make sure your subframe hitches together tightly and that the foam comes right to the edges. You could put a facing around the foam to protect the edges if they are going to be moved much, just have your scenery simple so it can be cut and repaired easily.
Have fun,
I didn't want to hijack anyone else's thread. I'm planning a layout in Florida in a garage. I've heard all of the warnings but it is the only choice I have. I will have a room built in the garage with at least a wallmount air conditioner. My current layout is based on HO modules and just has plywood, cork roadbed and then track. I'm wanting to use 2" foam for the scenery possibilites. I'm thinking that if I just use foam and skip the plywood base that I would help to reduce any warping concerns. I'm using Sievers benchwork so the "ribs" are 12 inches apart. Are there any downsides from eliminating the plywood layer in this instance? Thanks.