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help identify this damp/condensation patch


johnhenstock83

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hello,

 

I think I'm going mad here, I might have discovered the source to unlimited water out of nothing...

 

damp.thumb.jpg.2e72db04e95823fc7a1937ff47aa6622.jpg

 

when building our extension, we ripped our old kitchen out, including all pipes/cables/flooring. the floor is a concrete slab, probably uninsulated, but in good shape. for weeks, it was bone dry, despite builders working in/outside. the location in question is not near any old or new/existing pipes, valves, drains and so on. I seem to have a patch of damp that just won't go away, no matter what I do. I used an electric heater to evaporate it, it came back the day after. It's right under a brand new stud wall (2x4 timber, rockwool, plasterboard, skim) and doesn't contract/expand. since there's nothing underneath and it was always dry until the walls were built, I can only imagine it's condensation, but the location is weird.

 

can someone give me an idea what it might be and why it won't go away? it's not wet, just a bit cold/damp to the touch.

 

thanks

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22 minutes ago, johnhenstock83 said:

It's right under a brand new stud wall (2x4 timber, rockwool, plasterboard, skim) and doesn't contract/expand. since there's nothing underneath and it was always dry until the walls were built, I can only imagine it's condensation, but the location is weird.

Rule no 1, when something has changed, ask what has been done.

 

It was dry.  You built a wall.  It is now wet.

 

could there be a pipe under there not far from the surface, and a fixing (nail or screw?) holding the sole plate for the new wall has penetrated the pipe?

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there are no pipes in that location, I know that for a fact, but could it be that they drilled too deep in the concrete floor and created a link between the ground and the inside of the house?

 

it's a 1950s house, I don't think it has a DPM.

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Take a look outside, where is ground level compared to your DPC?

 

If it's not a 150mm below, that could be where the water is entering. Ours was pretty close to dpc for a while and we had similar.

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More info needed.

The wet floor is an original floor, but has only recently shown damp?

Was this area under kitchen units? What is on the other side of the wall? New or original?

Is it dry on the other side?

How far does the damp extend?

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yes, it's only been showing damp since the stud walls have been built.

 

this specific area wasn't under the kitchen units, but between ripping out the old kitchen and building stud walls, we're talking weeks in which there was nothing there, no damp either.

 

the entire area is the original floor, it's just a divider wall creating a downstairs cloakroom. pipes are far away from damp patch and not connected yet, so they're not leaking.

 

more or less dry, the patch is the corner you see and potentially under the stud. not much to see on the other side.

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In the words of Sherlock Holmes and ProDave 

When you have eliminated all which is impossible then whatever remains, however improbable, must be the truth."

 

I'd suggest airing the place until it is naturally dry then see if that is sorted. Might just be a wet slab from the building works.

What floor surface was there before?

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no pipes above the stuff wall. besides, the patch is only on the slab, in a corner, not anywhere else in/on/around the wall. could the stud wall, where it's been fixed to the floor slab, have caused a leak? i.e. the builder drilled through the slab and created a hole between the ground and the house?

 

I doubt it, as the builder is very experienced and all the work he did is sterling, I'm sure he knows not to drill though the slab or a potential DPM, but you never know.

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The scenario you describe I can’t imagine it’s anything other than a water leak from somewhere, somehow.
 

My experience is that a tiny  water leak takes quite a while to manifest itself and the water is coming from nowhere near where the damp patch is appearing. Our similar damp patch was half a meter from the slow and steady drip drip and not under the wall where the drip was coming from. 

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Do you have any faulty rain water goods on the other side of the wall?

 

soil on the other side of the wall?

 

the existing wall may have been able to breathe out the moisture before the new wall was built?

 

 

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so just to clarify, this patch is in the middle of the original kitchen, on the slab, nothing new has been built near it, other than 1.5 stud walls (timber, insulation, plasterboard). there are no pipes nearby, nothing is dripping and everything else is bone dry in and around the patch. if there was a leak, I'd probably see patches on the new plaster (it's very dry), or any spot in the vicinity.

 

it seems like the patch is slightly smaller now, so as long as it's not growing, I'm "happy", but I just can't figure where it comes from. maybe there's a cold patch in the slab and it attracts condensation. since it's just in a corner, it probably doesn't ventilate properly.

 

the mystery continues...

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the previous flooring was vinyl, fairly thin "plastic" flooring with something that looked like rubber on the back. you are right in that it would've concealed the damp patch if there was one, but before starting the construction work, we removed all of it and the entire floor/slab was bone dry, even during construction. again, this is INSIDE the original house, the extension has nothing to do with it. no changes were made to the existing slab and aside from those stud walls, nothing has been changed.

 

had this damp patch been there for a while, we would've seen it straight away after removing the flooring.

 

I'll give it another few days, it seems to have contracted a bit, but if it was just a wet spot (let's say from washing the slab or anything else), I'd expect it to be gone by now, it's not a huge patch. even the newly skimmed walls (drywall / plaster) dried up in less time or the screed in the extension. this seems persistent, but there's nothing fuelling it. no leaks, no pipes nearby, no ground on the other side of the wall (shared, covered alleyway, concrete at least 150mm below DPC). the only change from dry is the stud wall which was made with brand new, dry materials (stored inside).

 

I'll keep posting until I find out what's causing it, like I said, it might go away, but the duration tells me there has to be something there. either drilling through the slab when installing the wall plate or a cold patch that creates condensation, otherwise it would dry in half an hour...

Edited by johnhenstock83
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Do you have a water meter? See if it spins with all water switched off - or take a reading, make sure no water is used and see if it has moved over night?!

 

I know you are certain there are no pipes, but would you bet your house on it?

 

What are the water table levels like, could they have gone a bit deep putting in fixings, and created a route for ground water to come up? I would assume not but I have seen something like this where the house is built on a hill and water coming into the property was an easy route.

 

 

Edited by Carrerahill
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no water meter, but no water pressure loss either, everything operates as usual. bathroom is upstairs and sits on an old wooden floor, any drip would be properly visible on the white downstairs ceiling. ceiling dry, walls dry, pipes dry, I am 100% confident there is no leak. it's simply impossible for that location to be affected by any leak, physically impossible. even if there was an undetected leak, those water drops would have to travel to exactly that spot and that would leave traces or cause damp along the way.

 

house is on a plain, no hills, no rain lately, no DPC breaching, damp patch is too far inside the house to be affected by anything outside anyway.

 

weird, isn't it? if the builders breached the floor slab, I'd expect the damp patch to grow substantially, not cause a bit of (extremely slowly) contracting surface humidity (more like a cold, slightly damper than dry patch) as opposed to proper wet.

 

weird, isn't it?

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