Updated: for slab problems

[bsr]

Hello

On removing the skirting in a room I have found this hole. It is approximately 25mm x 25mm wide, 75mm high at the highest point. There is a noticeable breeze coming through it. I can feel a damp proof course under the screed; I can push a tape measure 120mm down below the floor level.

Any suggestions what I should do? A bit of foam to block it and forget about it, or is there something more serious to be looked at? Is it simple poor workmanship or something more?

What seems strange to me is that the hole appears to be in the inner skin, starting above DPC and finishing below it, yet there is no sign of cavity insulation in the hole (the wall was insulated with blown fibre).

I haven't filled it with mortar because I don't want to bridge DPC without getting some advice.

If it makes any difference, this corner is where an 80s extension joins to the original house. I have a nearby crack in the screed that runs the full length of the floor.

Thanks


bsr

 

[noseall]

It looks to me like the result of poorly constructed/compacted sub-base that has shifted slightly and allowed material to fall in it. Common amongst those who use large units of hard core without using finer stuff or a sledge hammer nearer the top.

I'm surprised you can't see any polythene though, even for an 80's job. It should be visible going under the internal DPC.

Filling it locally with say a cement grout will only yield limited results. I'd be more inclined to fill it with foam as there will likely be voids of a similar nature all over the floor.

 

[stuart45]

I'm surprised you can't see any polythene though, even for an 80's job. It should be visible going under the internal DPC.

It was common practice in the 70's to cut off the DPM flush with the slab to make it easier, so it was continued with some into the 80's.
BRE used to recommend 3 coats of black at the wall/slab junction to stop any damp at this point.

 

[bsr]

Thank you, I have noticed the same issue in another corner. I will foam both.

Next issue... The screed has cracked at the junction of the two extensions. Part has become loose. I lifted it, and it is 20mm thick over a piece of timber!

I suspect the house had a patio door across the back and when the extension was added the builders put some wood across the cavity and screeded onto it.

The rest of the screed seems to be in good condition. Can I repair the loose patch with some patch mortar or do I need to do more? I can lift the timber and concrete if I need to but don't want to be making work for myself!

 

[Ian H]

Might be better to clean the screed off and put 20mm of timber over the timber.

 

[bsr]

Noseall, you were spot on. I removed the loose stuff today and I have a sub base with roof tiles and bits of wood in

Seems disproportionate to dig up the whole screed since it's mostly sound and stable, so patch repairs will have to do. I am planning to use epoxy mortar for a strong finish.