I'm putting a small pump house inside an old barn under a floor. the ground is moist and climate does freeze during the winter season. what type of stone should i put under the concrete and how thick should i make it? The slab floor is only going to be about 4'x4', how thick should i make the slab? it wik have about 4 or 5 runs of block was on the slab. Can anyone tell me the best way to do the concrete work please?