I plan on creating a Great Stuff background... but since the foam isn't water proof, what happens when damp plants grow on it or it gets sprayed with water? Will it shrink?

When I make it, I'll be spraying the foam onto plywood (hint... hint... new viv coming up ), and then covering it with a thick layer of black GE II Silicone, is the silicone the reason it can resist water?

The background (and false bottom) I made in my Tomato frog (now houses chubby frogs) vivarium worked good, but for one, the chubby frogs would burry down 6+" until they got the the top of the false bottom, which I was afraid of them hurting themselves on the abrasive screen, so I removed the fasle bottom, and as for the background, well the frgs (and I) had no use for it, besides it was my first background and didn't work out that well.

Thanks,

~Royce