Replacing concrete floor slab, costs?

SameOldRoundabout

Has anyone had to replace a floor slab? We were aware there had been fairly significant internal settlement to our new house, and upon removing the carpet the original slab is cracked and very sunken. I’m assuming that it’s at its maximum sink now as there is earth about 20mm under the slab, if that. 

Does anyone have a rough cost to have it dug up and reconcreted? It’s about 2mx6m. The other half of the house (Living and dining room) has also sunk but is suspended flooring over a large void. Not sure what to do about that, I guess pack the joists up after the hall is concreted?! 

TELLIT01

No idea on cost, but if the suspended timber floor is also settling it might be worth considering replacing that with a concrete floor at the same time.  Massively disruptive if the house is occupied but a good long term solution.

SameOldRoundabout

Yeah, that’s something to consider, I’m just worried about costs spiralling. So far everything we touch uncovers more big problems 😭 Part of the whole owning-an-old house thing I know. 

FreeBear

How old is this house ?

From what you've said, it suggests that the slab forms the hallway - If so, any stairs to complicate matters ?

You are probably looking at four or five days to break up the slab, dig down sufficient for hardcore/insulation/concrete, and then another couple of days for everything to set. Then you'll want to allow a week or so for the finishing details such as plaster & woodwork repair/replacement. As for cost, really difficult to put a figure on it.

As for sagging suspended flooring - You really need to understand the reason for the "settlement" (same for the concrete slab). It may be possible to jack up the joists and insert packing pieces where they rest on sleeper walls. But if the foundations of the sleeper walls are inadequate, it may require more work. An alternative to pouring a new slab to replace the timber floor is block & beam - Would isolate the floor so that it would no longer be susceptible to any further settlement if any occurs. 

SameOldRoundabout

Freebear, thank you. Stupidly I hadn’t even thought about the time it’d take and the fact we won’t be able to live here while it done really will we?! Oh dear. The house is Edwardian, so over 100 years old. There is indeed the staircase in the hall. The house faces down a steep bit of hill, we think the settlement was caused by localised ground movement towards the bottom of the hill, which added to multiple now remedied issues (ivy and holly in the soil next to the house, a dried up stream running down the hill not too far away etc) . Most of the outer walls have been rebuilt in the 90’s (in fact right now we’ve got Helifix anchors going into one that hasn’t due to lack of lateral restraint causing bulging) and there has been no sign of any more movement since then, our surveyor was confident movement was historic and not ongoing. So it’s really a question of repairing what damage has been caused many years ago. I am a bit terrified though as we keep uncovering issues, rotten upstairs joists due to blocked air bricks, some windows which looked sound are actually rotten upon close inspection up the scaffold etc. 

Suz1949

Kitchen/diner and hall floor to be renewed with dpm and screed, £3660, plus £500 for two skips with permits.  The house was built 90 years ago and the flooring was Terrazzo.  It's cracked and is uneven everywhere stated.  It's a terraced house and the front room doesn't need doing as it has floorboards.

FreeBear

SameOldRoundabout said: The house is Edwardian, so over 100 years old. There is indeed the staircase in the hall.

Can I try to convince not to put a concrete slab down - A building of that age will (probably) have solid brick walls. Any moisture collecting under floor will be pushed in to the wall and cause damp problems. If you can, a suspended floor with good under-floor ventilation would be the best solution. This would allow any moisture forming to dissipate through the air bricks rather than up the wall. Done correctly, you could still benefit from having insulation fitted, and it shouldn't cost any extra.

SameOldRoundabout

FreeBear said:

SameOldRoundabout said: The house is Edwardian, so over 100 years old. There is indeed the staircase in the hall.

Can I try to convince not to put a concrete slab down - A building of that age will (probably) have solid brick walls. Any moisture collecting under floor will be pushed in to the wall and cause damp problems. If you can, a suspended floor with good under-floor ventilation would be the best solution. This would allow any moisture forming to dissipate through the air bricks rather than up the wall. Done correctly, you could still benefit from having insulation fitted, and it shouldn't cost any extra.

Oh really? That’s interesting. The walls are 18 inch thick solid stone. (Well having seen the internal skin, solid stone and rubble!) Currently in place is a slab of what looks like concrete, about 25mm thick, topped with the original tiles. It’s very badly cracked and degraded. Under that appears to be hard packed soil/ground. Would it be a bog standard builder to ask or someone specialist?

FreeBear

SameOldRoundabout said:  Currently in place is a slab of what looks like concrete, about 25mm thick, topped with the original tiles. It’s very badly cracked and degraded. Under that appears to be hard packed soil/ground. Would it be a bog standard builder to ask or someone specialist?

Quite likely rammed earth & clay topped with a limecrete (early concrete, but lime used in place of cement). Terracotta or pamment tiles usually laid on top. If the tiles were in good condition, it would have been worth preserving...

I would suggest talking to the guys over at Mike Wye to discuss your options - Digging out the existing slab and replacing with a layer of foamed glass & limecrete would be one possible solution. Not a job for a "bog standard" builder unless you have total control of the process and final say on anything/everything. Most of them are of the "bung a bit of cement in" brigade which you don't want anywhere near your property.

Mike Wye may not be available at the moment, so some light reading for you that might help the decision process https://historicengland.org.uk/images-books/publications/eehb-insulating-solid-ground-floors

SameOldRoundabout

Thank you again freebear. We’d hoped to save the tiles, as they’re perfect in the porch but in the hall they are all destroyed. The previous owner has spent 20 years attempting to patch the floor with self levelling or small bits of cement. They’re either cracked, missing or destroyed nigh on everywhere. Very very disappointing.