I was looking for something to loosen up a container soil mix and accidentally bought fuller's earth ( I was trying to get traction grit). The guy at the farm supply place said that it was fine for that application. Well, a year later, I don't think it was such a good idea. The stuff seems to have caused those pots to drain poorly in heavy rain and it seems to be clumping tagether like wet pottery clay. What is this stuff, and is it good to have in a container/potting mix?