Im going to need alot of fill for the new shop Im building. I was thinking of just using sand, because of the insul board for the slab. Would sand be alright? This is first time building a barn, and doing a radiant floor. So I wanted to make sure I dont make a record for most mishaps. Would a 4″ slab be alright or more? It will have a backhoe and 1 tons at most inside. Thanks guys