Weak Concrete Base to House

[jonesnick]

I have been stripping out a 1930's semi, and found that under the rotten wooden floor is a concrete base. The concrete base is approximately a few inches deep laid directly onto soil. When the house was built they ran joists in the concrete to fit the wooden floors to which have eventually rotted, and reduced the strength of the concrete base.

I have now dug out the joists and completely removed the wooden floor. I now have a number of deep gullys in the floor which I need to fill.

Therefore what is the best way to fill these holes (bearing in mind there is soil at the bottom of them)? I also want to strengthen the floor, i.e. make it more damp resistant. Would I need to lay a new concrete base on top of the existing base and then a self levelling screed damp screed? Any comments would be greatly welcome.

 

[Symptoms]

Nick - if the thin slab is generally dry (they usually are) and the only areas of concern re. damp are the joist trenches, then the fix is:

fill the trenches will concrete - use the bags of ready mixed stuff and pour in dry, it'll go off if the soil is moist.

roll of 4" wide DPM routed below position of new joists then place the joists on top.

build the floor as per the original.

If you've got enough space consider suspending the joists off the base on joist hangers.