subfloor void

I have a subfloor void in a room which has a unused fireplace of a 1930s semi in the north west of england. There is lots of white deposit on the subfloor void and when I dig the floor the ground is like clay. Is this deposit mould or salts? I cant see any on the underside of the floorboards its...

We recently discovered that ground floor living room of our Victorian terrace house is a concrete slab, under which is a layer of DPM, then sand, then soil. When we opened it up, we were expecting to find a suspended timber floor, with a void providing ventillation (this is what the neighbours...