I am currently renovating a 1847 French stone farm house.At Easter I dug out the internal floor (2.5 m X2.5 m) to asingle story out house attatched to the main house.My intention is to lay a slab, dpc, metal the floor, insulate and lay a 70 mm concrete floor. However, The stone walls are laid directly on mud ( no suprise there) which I have obviously exposed by 25 cm.
My question is do I continue with my plans or do I gently ( 1 metre at a time) remove the mud footings by half the thickness of the 600 mm wall and back fill with concreate .
All advise and comments will be greatly received.

Steve Mac.

Get the structural floor in fast.

You do not state how far the mud will below/above finished floor level. There are two threats: rising damp in the walls and instability stemming from your excavations. Putting in a concrete floor incorporating a DPC will very probably exacerbate damp walls as damp can no longer evaporate from the floor surface so the water table will rise.
Stability will probably be unaffected providing the mud is below finished floor height, has not been disturbed, and the concrete floor is laid without delay.
However, unless you are confident there is no danger of rising damp, then you probably need a DPC in the wall, so may have to excavate and under-pin anyway, incorporating a DPC.