Concrete floor

[jackflashh]

I am planning to fit a concrete floor in a single basement room of my house (the existing floor is incorrectly done). I thought I had the jist of what was required with a sizeable layer of compacted hardcore under about 100mm of reinforced concrete. However one of the builders I have asked to quote has thrown my ideas a bit, as he says he will need to keep digging out soil until he gets to subsoil. This could be quite a long way down! I had thought the concrete "raft" would sit on the hardcore and soil, and because load/area = force would mean there would be very little force projected onto the soil (other than the weight of the materials themselves).
Is he confusing this with a strip foundation for building on or have I understood this completely wrong?

 

[Deluks]

Habitable basement? Or storage/damp/dead bodies/spiders basement?

Anyway, 150mm hardcore, well compacted (can get away with 100mm if the ground is already firm, which having already had a floor on it, probably will be.)

Then about an inch of sand to blind it off, damp proof membrane (possibly pointless if the walls are damp but) then 100mm of concrete, A142 reinforcement optional (but makes it really tasty!)

If this room is in use, damp proofed etc then insulation will be required between sand/concrete.

What's existing floor?

 

[jackflashh]

Well the floor was never fitted properly 15 years ago, the builder ran out of cosh and just threw down some gravel and covered it with visqueen, ran some mortar around the perimeter and dropped some 4X2s on it then chipboard flooring (it is dry). It's been sinking for about 10 years (about 1" at one point), so now it's time to get it done correctly. The original spec was for a concrete floor.