Skip,
I guess it's a good thing I didn't read the instructions; I used the WS plaster cloth and stuck it to my 2" pink foam with no problems.
Don Z.
Research; it's not just for geeks.
I get my plaster cloth from the art supply places like Michaels and A.C. Moore, and my foam from Home Depot. They all play nicely together.
Does Lowes have the blue stuff? One's made by Owens-Corning, and the other by Dow, but they're the same, chemically and structurally.
But, consider this: Why not rough up the foam? The real world is not flat, not even over very short stretches. I cut and gouge my foam, and use the scraps to build it up in other places. These "microhills" and "microvalleys" are only a few scale feet high, but they make the terrain look much more realistic. When I'm adding a larger lake or stream, I save a bit of the Envirotex and add it to ditches and small-scale depressions. You might not notice these details at first, but on second glance they add a lot to the scenery.
It takes an iron man to play with a toy iron horse.