I have used the cork over 1/2" ply for decades. It always works. When short on funds I have tried OSB (a bad idea) and particle board (a really bad idea).
I once built a small switching layout (actually, more like a diorama) on foam insulation with a light wood framework. That worked really well, but I used sectional track (it was HO) glued right down on the foam with Liquid Nails.
If I were going to do an alternative, I would use the foam. But I don't know how you would attach cork road bed. Contact cement won't work. It will dissolve the foam. Liquid Nails (they make an adhesive specifically for foam insulation) might work, but making sure you don't have any humps or bumps would be a challenge. With full profile ties (see below) you might glue the ties right to the foam. A scale 9" thick tie holds spikes pretty well.
As for thinner plywood? Sure, but you will need more supporting benchwork. With 1/2" you can have supports every 24". With 3/8" or 1/4" I would think you would want supports every foot. So I can't really see the advantage.
One other point, with plywood, you want to be sure and use "AC" with the "A" side up, especially if you are planning on handlaying the track.
My ties are scale 9" X 60". Pretty typical for a "heavy" narrow gauge railroad. Lighter narrow gauge, like logging operations, would use smaller ties.
Stan, You're in Mass. and can buy sheets of the 2" thick blue or pink foam 2'x8'. Put this in a light weight frame. Then just use a vinyl caulk to glue the ties down. No need to spike the ties down. You can add cork if you want but it really isn't needed.
The good part with the 2" foam is you can carve stream beds and gullys into it.
____________________ Dave Mason
D&G RR (Dunstead & Granford) in On30 “All tyranny needs to gain a foothold is for people of good conscience to remain silent.” ~ Thos. Jefferson
“Those who hammer their guns into plows will plow for those who do not.” ~ me
Ma and Reg and others have it right, foam is a great material. That being said, cork adds stability and raises the track up slightly. Foam, cork, or both work great! I would caution buying cork from online though, unless it's meant for model railroad use. You need the cork particles to be small and tightly packed to be sturdy enough for the trains. Some lower grades of cork don't do well for model trains.
As I said, good luck with the railroad!
Last edited on Sat Jun 17th, 2017 06:03 pm by jtrain
Sorry Stan, didn't even know that vinyl road bed was an option. If it's not terribly expensive, I'd recommend laying a section of track using that section to test the different road bed options then use whatever you like best.
It would be pretty hard to go cheaper than cork though.