This clay material is basically straightforward stuff once you get a handle on the composition and that is a matter of experimenting with it weather you buy a pre-mixture, fabricated product or dig it out of your backyard. I have made it up with many different constituents. Depending on application I'll throw about anything in there including cow dung, hemp fiber, flax, straw, linseed oil, lime, pine tar, blood, piss, horse hair, glue, milk, eggs. Critical is the amount it's going to shrink when it dries and so the aggregate is the crucial factor. That is, the amount of sand for example.