earth floor advice

[ringer]

Hi all,
The floor of the lounge in our house is quarry tile over earth. i'm sure it's not been touched since it was laid in 1902.
We need to level the floor and and either reuse the tiles or lay a good quality wooden floor.
Its been suggested that I dig out the floor and replace with concrete, If this is the best way what depth of concrete would be suitable?
Being a bit lazy I want to know if there is anything anyone else can suggest to safe me a lot of spade work?
Thanks

 

[noseall]

i think digging out is the right answer. even with a decent hard core sub-base, most solutions involving membranes, insulation, sub floor etc require a minimum tolerance of 100-150mm or so.