It's a good idea but I would have thought as @julianf wants to store machines in the space, and head height is at a premium, laying a membrane and 4-6 in slab on top is probably not so great and the existing floor possibly sucks up damp, digging it up is more likely the best course.If it's compacted stone already and depending on the weight of the machines going in there, can you just concrete over it?



