why do you want clay in your stalls ? I have clay dirt. It does not drain. It hold the urine, its the grossest dirt around. It is slippery when wet, then it dries like a brick. It gets on your shoes and weighs a ton. If it dries in a hoof, you can barely pick it out..
My stalls started out with about 8" of sand on top of clay soil. Over a few years the moisture from the clay and the horse's hooves have made a fairly solid floor but nothing like cement. It is easy to clean. Urine seeps thro altho I'll throw a handful of diatomaceous earth on the pee spots. This helps absorb the urine until I get in there to clean.