I hope I haven't opened a Pandora's box with the suggestion that gypsum will amend clay soil. This was many years ago and I used it on a cubic yard that was used to fill a raised bed. I don't remember how much was used but I was buying it in five pound bags so it couldn't have been too much. As I mentioned in my original letter, once I mixed it in. I could pick up a handful and pour it out like sand. I also remember reading an article from a botanical garden that had a huge bed of clay. They didn't even mix in the gypsum but applied a layer over the surface and it worked it's way in. I will try to do some research since some members apparently tried it with no success. Cherry G