Replacement concrete floor

[Tristar]

Sorry about this, I mis-posted it under the wrong forum:-

I am about to replace a floor in an 1890's terraced house. The undersite is solid clay. While I appreciate that up to 18" should be removed to be ideal, what is the depth of slab that building control will accept? I plan to use a good levelling layer of sharp sand beneath the 1200 DPM on the clay, I then intend to use 70 -75mm of insulation. If I finish with a 4" polished concrete slab, I'm hoping to get away with only going down about 10". I shall have an insulating layer around the edge of the slab and be sealing the joint to wall with synthaprufe.
TIA

 

[noseall]

100mm compacted hard core.

25mm blinding (if you are really fussy with the stone).

80mm celotex.

100mm trowelled slab.

Tot 305mm.

You could pinch a bit on the hard core layer at your own risk. But why bother.

 

[Tristar]

Thanks noseall,

You don't thiink the clay will be solid enough to just take the blinding layer? Its as much about digging down and clearing the clay as anything, it is very difficult to dig out. My local builder who does these all the time says even the houses were built without footings on the clay layer, which I can confirm, so I was hoping a good blinding layer might suffice.

 

[noseall]

Clay is fine until the water content within begins to alter.

Characteristics of clay ensure that it is one of the most susceptible substrates to volume changes when water is subtracted or added.

The hard core layer may help counter this.

 

[Tristar]

Point taken, I will follow the advice.