Quote Originally Posted by John View Post
Emily, I'm a newbie to this background business and I've spent the last day doing some research. I've read conflicting things about bentonite. People say it will crack if it dries out. Is this true? Do you have to worry about it cracking? Any info you have to offer would be greatly appreciated.
If you have not already read these threads, there is some good information and pics in them

the deal with calcium bentonite - Dendroboard
Bentonite clay/ kitty litter - Dendroboard
Bentonite clay - Dendroboard

I once left out some bentonite for a month or so, it was extra I did not use in a tank, and later when I found it it was rock hard and inmalleable. Originally it was mixed with water but since it was not in an enclosed space, the water had evaporated out and binded the mix together. I added water to see if it could be used again, but it stayed hard and sharp.

Depending on what kind of tank you set up this could be a good or bad thing, if its for a more temperate species or a desert species you could mold a background and then let it dry out and you would get a rough textured surface. I'm not sure how well it would hold up long term, the dried out clay I had cracked but did not loose its shape at all. In a tropical enclosed vivarium you don't have to worry about it cracking. Even if its not super humid, when you first make the mix it gets saturated and it takes a while for the moisture to leave the clay, even when not in a viv. If you are worried about it cracking, misting it regularly would most likely prevent this from happening. Currently I have 5 tanks with bentonite backgrounds, and I have not had problems with any of them.