Bulging concrete floor in utility/cloakroom

[tobydog]

Unfortunately we have an issue brewing and it's been going on since we moved in.

Our small utility/cloakroom is a single skin brick (lined) lean to with a tile roof. It's 11ft x 7ft. The floor is tiled but I had a dispute with the surveyor after we moved in 11 years ago that he didn't pick up a damp issue in the floor during the survey. Despite numerous arguments, in the end he repaid his fee of £700 and we both moved on. At the time the floor was flat but overtime the central part has started to bulge, particularly at the toilet end. Also, I have to keep filing down the bottom of the entrance door from the house each winter as it keep catching. I put this down to swelling of the wooden door but I wouldn't expect to have to take something off every year.

I removed a fair amount of the cement floor where it butts up to the house soleplate plinth to give it some breathing space but noticed that the whole floor sits directly onto the soil below. Oddly, at one point there's a large void.

My question is, can I fix this problem without digging up and replacing the whole floor? It's not bad enough to justify that and it would need to be a limecrete floor as I wouldn't want a plastic membrane up against the main house plinth. Can I do a localised fix just were it's bulging? Self leveling screed isn't really an option due to the toilet and fixed built in cupboards. We could live with it but it's obvious in the toilet area and I feel I'm only putting off the inevitable for when we finally move.

Thanks

 

[RBailey]

Have you got any plant roots getting underneath and causing the push up?
If so killing them may help arrest / slow the problem.

Cheers,
Richard B.

 

[tobydog]

Hi Richard. We have an 8ft hedge quite close and it's been there some time. Not sure what it is but it has tiny leaves and isn't invasive. I doesn't look capable of lifting a concrete floor. Added to the fact that the floor tile grouting feels damp, my bet is still on the slab sitting directly on damp soil. A classic bulge inducer! Thanks

 

[88v8]

Is the room newish?
Perhaps there was a tree on the site and the soil is expanding now the tree is no longer taking the water.

Are you on clay? Clay expands & contracts with moisture.
Is there a leak under the floor... soil pipe, old/new drains, water feeds?

The floor must be jolly thin to be bulging.
I think I'd have it out.

Ivor

 

[Zebra]

Someone's tunnelling in?

 

[tobydog]

Hi Ivor. No, the room has been there for many years (50 - 100?) but has very shallow footings which might be part of the reason the floor is regularly damp. There were some sizeable holly trees next door but they have since been removed having died and blown down. It's noisy here today because the stumps are being ground out. The floor issue was there before they came down. The soil is generally free draining loam.

I've since had a better look under the slab (through a gap I dug it out alongside the main house plinth) and the slab actually looks to be just 2" thick at that part and sits on a very thin rubble base. No wonder it's moving.

The underground void is at the end where the outside door is, but the larger swelling is at the other end where the toilet is. So it could be a gradual leak underground around the u-bend but that doesn't explain the overall central swelling. The part directly next to the u-bend is actually fine though.

We're not talking about a big swelling. It's a shallow mound but enough for the grouting in the centre to come out and the tiles to pop off the bitumen sealer.

It probably does need to come up but it would be a real pain with partition walls and built in storage that sits directly into the floor. Could I cheat and just remove the central part where the problem is. I realise that would be a partial (bodge) fix but we haven't got the budget right now for a full excavation and a limecrete floor.

Zebra - no groundhogs or rabbits.

Thanks

 

[stuart45]

Sulphate attacks have been known to do this to concrete floors.

 

[tobydog]

Stuart - yes, I understand that concrete can react with sulphate contained in certain hardcores that used to be used as floor bases. My sister's 1930's house had to have the lounge dug up after it started growing upwards!!

From what I can tell, the thin slab is just sitting on a thin layer of broken tile and brick.

 

[stuart45]

Some bricks contain sulphates, especially if gypsum plaster is on them from internal walls. Normally needs a fair bit of moisture added to the mix.

 

[george2019]

Chemical attack is possible but the removal of the holly leading to clay heave seems a bit more likely.

In my experience loam doesn't extend much beyond narrow bands or in topsoil. Is the subsoil more clayey?

If you live in a blue area on this map I would suggest that clay heave is the most likely cause:
https://link.springer.com/article/10.1007/s10064-019-01621-z/figures/1

Also - you had a go at a surveyor for missing damp in a period house? Seems a bit harsh. Can usually safely assume it's all damp...

 

[tobydog]

George - The floor was moving before the hollies came down and it's been a very gradual process. They were also sitting at about 2ft above our driveway level behind a retaining wall. I have a feeling it might be the toilet piping under the floor although there is very minor bulging at the other end at the other end of the cloakroom so no answer for that. I'm ignoring that bit for now.

I've attached a photo. The toilet is immediately behind the door.

When I dug out our garden pond I went through top soil for about 6 to 8 inches followed by a progressively more sandy / light clay mix as I went down 3ft. Also, when a mouse / mole dug a tunnel in one of our flower beds recently, they shoveled out pure sand. Thankfully no problem clay but some of our neighbours have the occasionally heavy seam.

The problem with the surveyor was more to do with attitude. I could tell something was up soon after we moved in. He said he was experienced in older period properties but I've had more comprehensive and helpful Homebuyers reports on modern houses. Lesson learned but this is our first period home (1640's thatched timber framed!)