Inorganic, non-porous mounts?

[Flowers]

I'm not sure if this is the right section for this thread, but here it goes anyway:

I need an inorganic, non-porous mount for some of my Pleurothallids. I'm currently using tree fern, and I really don't like it. Sure, moss grows on it pretty good, and it looks nice for a while, but I'm getting sick of the slime and fungus that grow on/in it. It seems like, no matter what I do, I can never get it looking un-sickly. Most of the mounts I've seen of other peoples well established, fantastically grown plants look super clean and healthy. What are they doing that I'm not? So, I've decided to try and move away from tree fern. Does anyone have an idea of something inorganic, that the plants/moss can grow on, but not in? I also want it to look at natural (color wise) as possible.
(I hope this post makes sense, it seems a little on the rambling side to me.)