I have an old house(1830)and the basement still has the old dirt floor from when the place was built. I want to concrete over the floor and use the space for storage. The walls are mortared stones and bricks-in good shape. What is the proper construction of a concrete slab? Is it heavy plastic sheeting, then sand, then gravel, then concrete? Can I just use sand instead of gravel? I will have to pump it into the basement space. Probably using Fibermesh concrete mix to make it strong.