I just wanted to update this briefly. I just finished experimenting with a method of using concrete for a background in an aquarium. While it wasn't made for orchids, the method provided some nice satisfactory results for a background. The porous parts on the top that are exposed are currently filled in with the moss I use and I'll be planting some orchids on it.
Planted Glass Boxes: Aquarium projects: planted and bare
I think this process would work great for anyone wanting to build a drip wall and incorporate driftwood into that. If I do any smaller terraria I'll definitely look into it. There's a number of dyes you can add to the concrete patch kit to make an appealing color to you. The texture is also very nice and I think would work well for planting.
As I mention on the blog, I'll be in Panama the next few months and I'll update the blog as I can, but with 'field inspiration' instead of home gardening. I hope you will continue to check in.
Lastly for those of you hip to facebook, here's a link to the Planted Glass Boxes page. I encourage you to "like" and spread the word to those you think would be interested.
https://www.facebook.com/pages/Plant...04687772900296
Good luck with your terrarium gardening projects.