John - I initially used the Tetra brand, as it was carried at Home Depot, and black... and it wicks water. If you check their website, it is listed as an open cell polyurethane foam (it took some digging...). I'm sure that there are other brands out there that are in fact closed cell (besides Great Stuff), but I couldn't find them.
If used in a primarily aquatic enclosure, that shouldn't be a problem... but I used it in a paludarium with a fairly large terrestrial area, and a waterfall. It took three complete tear downs and re-builds before I figured out what the issue was.
Also - Great Stuff has a black foam, as well as a black Pond and Stone foam. I strongly suggest sticking with them, unless you are making an entirely aquatic set up.
As for axolotl's question -
Youtube is your friend... I'd suggest checking out the following:
- SerpaDesign
- Slithering Salamander Scapes
- Biotope Gallery
They all have great builds, with very useful commentary. It's a deep and useful rabbit hole...
Aquarium safe silicone and either sand or rock dust/fragments looks great, both emersed and submerged... I also like the look of rubbing/pressing is ABV or coco fiber as well. Play around with it, and you can make something that looks great and very realistic.
Cyanoacrylate (super glue) is a good adhesive as well, and is plant safe when liquid, and critter safe when cured.
I would stay away from grout and liquid cement - depending on what you're doing, I doubt that they are ultimately critter safe.