Great Stuff

I am planning my first terrarium. I went by wal-mart yesterday to check to see how much they had of what I needed. I was surprised.
Anyway, they have the Great Stuff expandable foam I have seen mentioned several times in terrarium construction. I have a few questions about it.
I want to shape it into waterfall. I plan on coating most of the foam with black silicone, then co-co bedding. But I hope to shape out sort of a rut that will carry the water diagonally down the side and spill out a few inches over a small pool at the end of the aquarium. It is the surface of this rut that I am concered with.
How does this stuff hold up when water is ran over it? Does it contaminate the water? Should I coat the places where the water is going to run with something, like mortar or silicone?
Also, speaking of silicone. I have read several places to use black silicone to hide the false bottom and to help keep things in place. Is there anything I should be aware of when I buy silicone? Does some silicone have things in it that are bad for frogs or plants?

[Arklier]

Great Stuff is a sealant used for stuffing up cracks and holes in houses. So it has to be waterproof. People use it for drip walls and stuff like that, so I doubt it will effect the water in any way.

As for silicone, just make sure you get 100% silicone. They sell stuff specifically meant for aquariums at the pet store, but it comes in tiny tubes that are hard to work with, and it costs an arm and a leg. You can find aquarium grade silicone in caulking tubes at http://www.fantasticfrogs.com. Or just do what I did and buy normal 100% silicone caulk at the hardware store. It was only $6 for the tube. While it says it's not for aquariums, I don't see how that could be possible if it really is 100% silicone, so take that with a grain of salt.

[Ridge]

You can use the Silicone II product made by GE to cover the foam, it is the best silicone available and is harmless once cured. I hope you are patient though since the foam is not easily shaped (when being sprayed) or covered with silicone (when dry) if you have never used this method before. Spreading the silicone so that it is competely covering the foam is difficult but possible. There are other products out there that you can use also. True the foam is waterproof when intact but when you do cut and shape the foam after it cures, pourous areas will be exposed and may allow water through. You are better off using a bicycle tire intertube or cut a piece of PVC pipe to shape your water channel and then silicone gravel to that to hide it.

[Arklier]

GE Silicone II is what I was referring to in my post. It's great, and much cheaper than the specialty aquarium caulk. Then again, I'm not caulking aquariums. I use it for sticking stuff to the walls of the aquaurium, not sealing it. If I were actually building a viv from scratch, then I'd go with the specialty stuff.

Anyway, as for Great Stuff, I've worked with that too. It is very difficult to shape, because it's extremely sticky. Even when it just comes out it's got the texture of warm chewing gum. My suggestion would be to get some large tongue depressers from the drugstore or something else disposable to shape it as best as possible. You will not need silicone to coat it, as the surface is very tacky for quite awhile. Shape it, then sprinkle dried Bed-A-Beast or other coir product directly over it. Black Jungle has a tutorial on their web site showing how to do it.

[*GREASER*]

Arklier have you skiped the silicone step and aplied the coco bedding right to the great stuff, Or do you know people who have? And how did it work?

[mindcrash]

I skipped the silicone step and applied the coco bedding straight to the wet great stuff. Worked just fine for me, and looks great.

[Arklier]

Originally Posted by *GREASER*

Arklier have you skiped the silicone step and aplied the coco bedding right to the great stuff, Or do you know people who have? And how did it work?

I haven't personally used it for a whole background. I've used it to stuff cracks in tree fern panel backgrounds, and sprinkle coco bedding over it.

great stuff is polyurethene foam and thus is an alkene so contains only hydrogen and carbon atoms but is it completely non toxic?

i have found shaping pre cured great stuff an exercise in futility. powdering it with coco works well, but beyond that i would not stick anything, branches, driftwood etc, into the greatstuff. when the greatstuff expands it is due gasbubbles expanding within the foam, when i tried sticking driftwood into the freshly applied goop it changed the way the foam expanded, and seemed to deflate the foam making the finished product was more compact and stiffer than my desired effects.
I like the pvc idea for the river bed. It may appear a bit unnatural being completely straight, but there are design ideas im sure you could employ which would lessen this effect.
good luck and keep us posted on where you take it

You can silicone gravels on top of the pvc pipes to create a more natural flow for the water.