Wow, great score on the cork, Anna. Every year or two, I buy myself a big slab of cork, about 18in. x 30in. and the last one I bought cost me $37. I break off right-sized pieces and mount orchids on them happily. The only down side is, the orchids probably need to be watered more often when they're mounted, at least until they're well established. On the up side of that argument is that it's nearly impossible to over-water an orchid mounted on cork. Here in FL with our high humidity and sometimes daily heavy rain, that's a great thing. Not so great for people growing inside their houses, although in your greenhouse it will probably work well, too.
I have Phals, Catts, and Brassavola types mounted as well as my little Howeara. At first I mounted them traditionally, with the cork piece vertical, but now I suspend them with string, and mount the orchids on them horizontally like a raft. They hold a bit more water this way, and I think they look prettier, too. I use the hollow side of the cork facing upwards as the 'dish' for the plant, so you can still see the nice cork bark texture on the underside.
