Basement Flooding - Tanking Fail - calling PigletJohn

[52andblue]

Or anyone else with Damp / Flooding experience please?

I have an 1880 Sandstone 4 story house (originally basement and ground floor, top two floors built and completed in 1880)
The basement level is totally below ground at the front & 2/3 below at the back inc windows. There is a back door at g/level, & 3 steps down.

When we purchased in Aug 2006 the tanking work which was commissioned by the sellers (as a provision of their own mortgage - they bought and sold in about 9m! after a divorce they said) was still wet. It was 'DPM' with a concrete topping'. It had a 10 yr guarantee.

It has failed.
There were damp patches on the walls and damp smells in the first year. We called the contractors back. They were so aggressive that I thought they were going to hit my then husband. They repainted a wall and tried to charge extra. With hindsight I should have called insurers.

The main problem is that the floor has joins in. When the water table is high water ingresses through those joins. It has never been more than an inch, it is not every year, we have put up with it and not claimed on insurance. Now however, we have 6" in the basement. I am not sure if we can claim on the insurance, I will need to speak to them.
We don't live in a flood area / near a river but the lane at the back can flood under the cottages behind us doors annually. Our water comes up through the floor, not under the back door as we have a good drain outside the back door so we are not subject to 'local flooding' at all.

My worry is: we cannot have the current flooring drilled up. We live here, & it would be massively disruptive / not poss to move out. The house is sandstone blocks, and there has been historic movement over the years (not serious but don't want to cause any more!).

Is there anything that could be done, to make it worth an insurance claim, to layer over what is already there please?

Tagging @PigletJohn . He does have so much knowledge.

I don't understand how your floor has been laid. If it was a poly sheet with concrete over it, the concrete is only to hold the sheet down with its weight to stop it floating up. The poly should be in one sheet, or lapped and taped. My neighbour did this, as water comes up his cellar floor at high tides (but omitted the polythene so he still gets a damp slab). I suppose if the water was greater than expected it could push the slab up.

If it was meant to be a waterproof concrete, it would be laid in one slab, with reinforcement, to prevent it cracking.

Do you think the water is coming through the walls and lying on top of the slab?

I think I might be looking at addressing the source of water. Are you in an area with a high water table? If not, water labs can test a sanple of the water to see if it is from a watermain (chlorinated) or a sewer (contains soap) or a ditch (contains leaf matter) or a spring (don't know). Your water and sewerage company probably has, or knows, such a service, as they are often used to identify leaks.

Do you know what the subsoil is? in some districts you can excavate a sump and put a pump in it. This is not done in clay soil, because the water will wash the clay into the sump, and pumping it out will leave a cavity. A sump does not involve taking up the whole floor, maybe a pit about a foot cubed.

Sometimes it is done uphill of the house, to intercept water running towards it, or a ditch is dug to divert the water round the house.

You probably need a local chartered engineer with experience in flood and water defences.

painting waterproofing on the walls often fails because water pressure pushes it off. Modern practice is to lay a floor with a void under it, and walls spaced off the structural walls, in the expectation that water will collect behind and underneath and can be pumped out.

There are two rooms (15x`14, and 12 x 16) there is also a long corridor connecting them and two large cupboards. All are divided by internal walls going down to the ground with original wooden skirting and architraves, none of which were removed when the tanking was done. So no DPM was run under the interior walls in the basement although the water doesn't seem to be coming from there especially but in the gaps in the cement that can be seen. The products used were Biokill Crown coatings. (SBR bonding agent, salt neutraliser, cementitious tanking, expoxy bonding, expoxy tanking, membrane system'). That;'s all I know I am afraid.
The cement was applied in a hurry and is not flat and has big ridges in. The contractor fell out with the previous people and didn't 'finish it to his usual standards' he said when he came back (before he got aggressive). Plus he said they 'refused to remove the wooden architraves and skirtings so he couldn't fix behind it'. I don't know?
The floor has a join between each room and corridor where concrete has been laid in stages. This gap is only really around 2mm wide but the water just pours in. The water comes up through those gaps and floods the floor it is worse at one end of the basement but the whole thing filled 6" deep in a few hours at the weekend.

The local soil is 'alluvial, possibly mixed with brown earth' but probably not clay. The original basement floor was soil and the original road was level with the basement but it was raised about 1 metre around 80 years ago and tarmacked.

Presumably a sump would involve drilling up a metre of the floor and that then being unusable as floor from then on? Plus cost £££££ ?

found a better map - its definitely Alluvial soil

you can put a hatch or lid over the sump so you don't fall down it.

your tanking doesn't sound much good.

'High water table' - there is a small stream running under the lane 4ft behind the basement- the local water co says the pipe is adequate and its the councils responsibility, the council say the opposite ... when it rains hard the water bursts up out of the drain, floods the lane a and goes ybdwe the doors if the cottages across the lane.
But its really a Qu of how to improve the Tanking I think ?
Am in Scotland so dont know if Chartered Surveyors the same here?
Would the 1st port of call be the Insurance co?

you could give them a try. I don't know.

Ok, thanks.
I think I need to understand better what different kinds of tanking are available and might be suitable.
I'm not sure whether to start a new thread for that or to call in Surveyor first (as presumably he won't advise about tanking and I know what type of water it is, and where it is coming from)

If you are sat on alluvium, it’s an old river course / floodplain. Likely highly permeable, hence the rapid rise and fall of the water table.

British Geological Survey (BGS) have a large library of borehole records freely available on their website. Good place to find more detail of local geology and historic ground water levels. Environment Agency also have some (few) active ground water monitoring points.

@Geekygeek - thank you. Yes the local village river is around 1/2mile away but has never flooded our part of the village in living memory. It might have been different in the geological past though!

I would have a look here
www.heritage-house.org/damp-and-condensation/all-about-the-pca/property-care-association-rising-damp-and-facebook.html

I have seen damp sellers made worse by tanking etc, remember who ever built the house would have dug it by hand and checked the water table etc. Friends have recently had issues as next door got rid of the sump pump and tanked his seller causing the water to flow in to his.
Usually its best to have a sump and let the water in keep the seller vented and all usually well

It really does not sound as if your damp proofing was effective. Any gap, even 1mm, is plenty for water to get through. The fact the damp proofing does not travel behind skirting boards is batshit. Tanking is called tanking because it creates a waterproof tank, not a bit of cement here and there . Water will always find a way through any gaps.

What do you use your cellar for? Your choices are: (1) accept that it will sometimes have water in it which will be worse after rain and dry in Summer (2) put in a sump pump which will keep the water level down or (3) re-tank your cellar.

Unless you really need the space as living space I'd avoid (3) as it is likely to cost a lot and if your current tanking is crap it may all have to be removed, so messy too.

I lived happily with option (1) in a previous house and I just accepted that was how that house worked. It was built in the early 1700s so had been doing it for a fair few years. Trying to keep the cellar dry would have been more harmful to the house. I lived there 8 years with no problems.

(2) is the option many people take and is reasonably cheap. Excavate a small sump in the lowest part, sit an automatic floating pump in it and you are done.You need power and somewhere for the hose to drain to. My area has a lot of underground streams and old houses and this is the option most people have taken. Your cellar will not be living room standard but it should stay pretty dry.

@Funf
@JoannaDory

thank you for your suggestions!

I'd prefer to have the cellar as living space yes (bought the house because of it, aiming to run a business from it so need dry storage space (not client facing space) but tech den space for Teens too)

I really don't want to drill up what's currently there. There are 3 stories of big sandstone block above it with huge heavy chimney stacks etc so I'd be very nervous of drilling affecting structural integrity?

So I thought I could either try to put a further layer of Tanking on top of what is there ? as the breach is via 2/3 hairline floor cracks in an area around 2msq where the corridor turns

And / OR install a sump (but assumed that would cost thousands?)

difficulty with just 'letting it do its' thing) is that it can go 2 years without water ingress, then fill 6inches deep in an hour. This can be in summer as often as winter, so I can't keep much in the basement and go away even for the day with things as they stand so that's really depressing and limiting. As it's the whole reason I bought the house and I need to use it to start a business and I can't move then I've got to do something to improve it as this is the worse it's ever been.

If you want a habitable room down there, I reckon you'd need to take up and relay the floor in that room at least, and line the walls.

You'd probably have a pumped sump for the other rooms, and powered air extraction to prevent damp diffusing into your habitable room. You would need a better contractor. Pumping will reduce damp and stop flooding overall, if the ground is suitable.

Taking up the floor and lining the walls enables you to improve headroom and insulation.

Quite honestly - you need a civil engineer to advise. Possibly one who understands drainage and structures too! I’m married to one so they do exist.

My mum had a similar problem many years ago. You will probably need to move out. It’s vital the work is done though. It’s no different to digging out and tanking all those new basements in London. But a structural engineer needs to advise too. You are not taking out walls but you could be strengthening foundations. You really need qualified advice for this. It’s vital in my view.

Your Insurance should be helpful in this too and they will need a report from an Engineer who knows what they are talking about. This isn’t a minor issue. The previous work was not good enough for the current conditions. A 10 year guarantee rather says it was a temporary fix!

Ugh...
don't like the thought of the house crashing down on top of me @PresentingPercy but don't think that's likely?
The basement (was ground when built) and now ground floors are pre 1880 (prob about 1820?) earth floor and single story sandstone. Then the top 2 floors were added in 1880. The road was raised around 1970, making the basement fully underground at the front of the house and half underground at the back. It will have been subject to flooding on and off for all that time i expect. The previous people had the Tanking done as a condition of their mortgage funds, but failed to pay the contractor 100% of the money so there was bad blood going on (plus they did a poor job and were cowboys when they visited us). There is some structural movement to the house but it is old and we had a full survey done and it raised no issues in 2006.

You don’t really know what foundations you’ve got and you don’t know where the water is coming from. I don’t think the previous “tanking” was good enough and you need expert advice from a consultant. As you would if your GP wasn’t sure about an illness. Speculating here isn’t going to solve anything. Looking at every contributing factor and designing adequate solutions to meet modern day rainfall and water levels is what’s needed.

@PresentingPercy
I agree with much of that and appreciate your input.
I don't think it compares to modern London basement excavations and wall removals so I was giving some more details in case helpful.
I agree that a Civil or Structural Engineer on site is best (I do know where water is coming from so that is at least a start, though water Co and Council both refuse responsibility so thats a can of worms)

No it’s not a wall removal but living below ground level always needs designing to take account of ground conditions. It’s never cheap. No one wants wet walls and damp smelling living conditions.

Yes, I see that @PresentingPercy
Thank you for your suggestions.
Sounds like I need both a structural engineer and a civil engineer then?

I would speak to any local Civil Engineering consultant that does smaller works. They often have a structural branch. Let them decide who’s best for this project. DH is Fellow of both institutions but I think he’s a rarity these days. I thought civil in the first place when you talked about drains. But Structural might be better for sorting out the design and any remedial work. Just talk to a few and see what they say.

If you do get work done, do please take some photos and let us know how it went.

Thank you @PigletJohn and @PresentingPercy.
I do appreciate the good advice and
I will let you know if things progress.
(thanks also to @Funf and @JoannaDory)