Damp patch on kitchen floor

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Hi all, newbie poster but been lurking and reading loads since buying our 60’s build end of terrace that needs lots of love back in mid-June!

I’ll try to keep this short, but looking for some advice (will call in a pro if needed, of course):

2 weekends ago we ripped out the old kitchen to prepare for a new one being fitted end of Aug, incl preparing a new floor, sorting out the electrics and re-skimming the walls. Upon pulling out a base unit I noticed a slightly damp patch on the floor beneath, but it dried up literally overnight so assumed it was due to something being trapped under the base unit and not allowing airflow.

Fast forward to yesterday, we were just working on getting some of the old tile adhesive off the walls and we noticed the damp patch was back in the same spot. Bare in mind this has been uncovered for the last 2 weeks, we’ve not noticed it before and is in plain sight as right by the front door.

The waste pipe runs down this corner and is boxed in (typical of all houses on this street) so we removed the bottom panels to get a better look. The boxed in section was packed with old sponge and stuffing similar to what you’d get in a stuffed toy, and full of debris like newspaper strips/bits of wood/an old lipstick(?!) and just lots of dirt and build-up from goodness knows how many years. We cleared it all out and checked for a leak in the pipe by running the shower and sink taps, nothing showed up. It didn’t get any wetter.

Checked outside - there is a small patch of repointing that needs doing on the external corner. We cut away an overgrown bush to have a closer look and saw nothing on the outside that suggested any issues - the brickwork and earth was bone dry and seems to be below where the DPM would be.

Also to note, there’s no dampness on the internal walls around this floor patch, apart from a little bit that must have seeped up - no more than an inch or so. Nothing higher up, and nothing on the ceiling.

Could it be the waste pipe has a slow, undetectable leak around the seal where it goes into the ground? Or could it be the little bit of pointing that’s degraded?

As I said I am happy to get someone round to take a look, but conscious of “damp proof experts” selling silicone injections. Pics attached (and please ignore the old water damage on the green wall - this is from a burst filter tap pipe that has since been removed).

TIA, and apologies that it’s such a long post! Some pics attached, including outside.

Taken yesterday after clearing out the debris:




5619FAB5-15DC-45B0-B279-185EC12986B5.jpeg
3878B8CE-FD77-4BF4-90F4-22E55E0C0B2C.jpeg


Outside:
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This morning:
8B4BAF8B-601E-4E43-B6C8-5F81A6BD0FBF.jpeg
A747E844-1300-4991-908C-D0FAB0B837A2.jpeg
 
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JohnD

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yes of course you have a plumbing leak.

is this a concrete floor?

or a chipboard floor with a void underneath it?

clean the above-floor pipes very thoroughly and blow talcum powder over them from the palm of your hand. the tracks of any water runs will then be easy to see. Also clean off the green verdigris on the water supply pipe coming up through the floor and blow talc on it.

the leak might be above where you are looking, and water might only escape when you empty a bath or flush a toilet.

the duct usually contains water pipes as well as the soil pipe so it might be one of them.

A tiny leak in a water pipe buried in the floor is not rare, and can cause a lot of persistent damp.

Avoid sealant paints and silicone injections which are useless.
 
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Hi JohnD,

Thanks for your reply. As far as I can tell the floor is just concrete - to the left there is the waste pipe for the sink/washing machine that emerges from solid concrete. Survey prior to purchase stated concrete flooring for the ground floor.

We have had a plumber round to move some pipe work prior to the new kitchen being fitted and he also removed an old water softener. Would it be worth getting him back over to look into this, or will it need a different tradesman?

Will try to get some talc today to see if that highlights anything, good tip. We do not have a bath installed (shower cubicle only atm - bathroom reno is next year’s project) but can’t say we’ve noticed any leaking from that pipe when showering / emptying full sink / flushing toilet.
 
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Update: had our plumber come out to take a look and he identified a slight hairline crack in the cement collar at the back of the stack pipe which is allowing water to seep through slowly, causing the dampness and why we can’t really spot it when testing flushing etc.

Going to remove the old cement and re-do it, hopefully that’ll fix the issue. He’s satisfied there’s no problem with the mains water pipes, and there’s no leak he could detect from further up the stack pipe even with rigorous testing - it’s dry as a bone all the way up.

Also not helped by the state of the pointing in that external corner that happens to be on the DPC, so going to be looking into that too.

Thanks for the suggestions!
 

JohnD

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I can't see a cement collar. can you show me?

soil pipe comes in lengths, and each fits into a socket of the one below. Unless the pipe is blocked at the bottom, and full of water, I wouldn't expect a leak out of a socket.

Is the socket at the bottom brown fired clay, like an old brown teapot?

the pointing may have been eroded by long-term leakage, though I only remember seeing that on old houses with lime mortar.
 
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Here it is - think it was obscured by the wooden frame in the original pics. I can’t get a clear photo but there is a crack at the back in the cement (?) where that darker damp patch is showing. Currently airing it out by keeping the window and door wide open so it has dried off considerably already.
98267DE9-5FAF-46C7-B1F6-AEB42E208D4D.jpeg
 

JohnD

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ah yes, that is the socket of a salt-glazed clay pipe

mind you don't crack it. I think it may already have a crack, facing the camera, which may continue under the floor. I suppose you could put your hand throught the access point and have a feel or squirt a hosepipe and see if it leaks out.

it has evidently been leaking for a long time.

you may be able to scrape the mortar out.

the joint is fundamentally inflexible and has no give in it to accomodate movement due to expansion or settlement. It would be quite difficult to repair, being in an internal corner and set in concrete. I am a DIYer and have done several outdoor ones, and a couple set in a floor with enough working room to excavate. The outdoor ones are much easier. If it is only the socket you can get a plastic repair piece that slides down into the old pipe, and the plastic pipe above fits into it

have a look under the nearest manhole cover to verify waste is flowing away freely.

carry on with the clean and talc test in case there is water coming from above. It seems to be round the back.
 
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Cheers, really appreciate your input :)

Think we are going to leave this one to the pro - we’ve enough to focus on at the mo with other bits and bobs that need wrapping up (and this kitchen has given us enough grief, I’d probably take my stress out on it and completely destroy it leaving us in an even bigger mess ) - I know he’ll do a decent job, he’s done loads of work for us so far and it’s all been stellar, he’s highly recommend in our local area and looking at his reviews it sounds like he did a similar job not long ago.

Re: checking the waste flow, he did mention he’ll check that when he’s back before he starts the work on Weds but will double check with him to make sure.
 
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check that copper pipe in photo it maybe pinholed .
Crack in cement collar i doubt you would be getting that size of damp patch i would def be looking higher up the pipe
 
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Our plumber has thoroughly inspected them. We’ve tried the talc trick, nothing coming from higher up the stack pipe or on the copper piping.

Suspected blockage at the base which is causing water to seep through the couple of cracks in the collar as it backs up slightly. It hasn’t got any worse over the last couple of days despite high volumes of water flowing through from showering etc.

Plumber is coming over tomorrow to look properly, he couldn’t get the access cap off as it has seized (seems the previous owner did not look after the property at all) so will be looking to replace that.
 

JohnD

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I think the water is on the wall behind the pipe, and is soaking into the socket where it touches.

This would be a leak above.

See how the damp level is much higher on the plaster behind the pipe.

Strip off more of the duct box for a better look.
 
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Morning! Further update, thought I’d post in case it helps anyone else in future experiencing the same issue.

Definitely no leaking from above, as said before the stack pipe and surrounds are completely bone dry. The dark patches on the walls are not damp, it’s just filth and discolouration. Our plumber chipped off the concrete collar and uncovered a can of worms - total bodge job by the previous owners.

There was a crack in the clay pipe (below floor level) but instead of fixing it properly they patched it over and put an extra clay collar on (not fixed in place, just left loose on the opening of the clay pipe) and then cemented to secure it to the PVC stack pipe. Instead of the plastic pipe fitting into the clay pipe, it was just left to swing side to side over it.

Plumber said he can concrete it again but it won’t guarantee the issue won’t happen again in a year or two, so got a drainage specialist in to take a look. Camera survey showed the crack in the clay pipe extends almost the whole way along vertically, and there’s some root growth causing more cracking. It’s these cracks that are letting the water seep into the ground around it, so it’s coming up through the floor in our kitchen that way.

Pipe is being fully replaced today and we’ll be good to go! Thankfully it’s only a small amount of internal work and the rest is external, so minimal disruption.
 

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