I saw some threads last year about adding lime to clay to stiffen it up in order to build a patio above. How much lime do you use? Do you till it in and then run the compactor over it? Anything else I should know? In the past we have just dug down extra deep and replaced clay with gravel. It seems like where people have clay it is bottomless-several feet or more deep, and we still have shifting problems sometimes when we use our current method.