Mystery wet patch on dining room ceiling

[EcclefechanTart]

Today I discovered a big wet patch in the middle of my dining room ceiling. Above the dining room is my bedroom. I located the corresponding place on my bedroom floor and pulled up a floorboard - to find a bunch of wires for the electric wall socket, a load of dust, and nothing else. It's not wet at all in the bedroom and the wet patch is nowhere near pipes, or an external wall.

It's a mystery. Any one have any explanations?!

[CheeseBadger]

Water can be quite cunning like that. It tends to choose a hidden and unexpected escape route. I'd be looking for leaks from the inevitable nearby upstairs bathroom. The route between there and your dining room ceiling may be around or under a joist. If you have plasterboard ceilings I'd be surprised that you haven't found the cause from your sensible sounding investigation. If it's lath and plaster, all bets are off and you should treat every piece of plumbing in the house as a murder suspect.

[EcclefechanTart]

Oh god, it's lath and plaster. You've frightened me now! The bathroom is at the other end of the house altogether though.

[HarrietSchulenberg]

Central heating pipe? Ex-inlaws' central heating leaked through their bedroom floor into the dining room ceiling. Pipe wasn't visible on first inspection as it was under a joist or something, more part of the dining room ceiling than the bedroom floor, iyswim.

FIL did a temporary fix with plumbing tape until they could get a plumber to replace the pipe.

[EcclefechanTart]

Hmmm...interesting. Couldn't see any pipes but, as you say, it could be hidden, and would explain why it seemed dry under the floorboard. Would the central heating start leaking randomly while switched off (since March) though?

[HarrietSchulenberg]

If there's water in the pipes, and there will be unless you've had reason to drain them, and the pipe deteriorates, it will leak. Could be a pipe joint seal that's leaking too.
Disclaimer: I am not a plumber but have a very leaky old house and ex-inlaws who are good at DIY.

[EcclefechanTart]

Right, while MN was down I have been exploring further! I pulled up the floorboard again and the one next to it but I simply can't find any pipes. I can see the backs of the laths and plaster but nothing else apart from wires. I am stumped.

I have also remembered that when we moved in a couple of years ago, there was a smaller stain on the dining room ceiling in the same spot, but it had dried out already. This is obviously a long-term thing, but I'm damned if I know what is causing it.

[Seeline]

I once had a leak from a water pipe - it was like you get with a hose. Just a tiny hole, with the water in a tiny jet arcing out. It took me ages to work out what was causing the soggy patch on the carpet in the middle of the room. The pipe was the one leading from the radiator, so not even under the floor boards.

[LowlLowl]

Wet patch on the CEILING? I'd say someone has been being rather acrobatic. At least its not possible to sleep in it.

[dingit]

Have your dc spilt anything? I knocked over a glass of water in our loft bedroom, which went through the floorboards and stained dds bedroom ceiling below.

[wowfudge]

Is it actually a stain which is now showing through the paint?

[blaeberry]

If you get a water stain on the ceiling then you have to seal it before you paint (get stain sealant from diy shop) or the stain will gradually start to show through.

[EcclefechanTart]

This is no joking matter! I am terrified of the idea that my lath and plaster will collapse. I read another thread somewhere that said you could get a rough idea of the mess it would create by putting your head in a 60-litre bucket of soot and shaking it violently

I did wonder about DC spilling stuff, but I don't think so as they don't have food/drink upstairs. And wouldn't it be wet under the upstairs floorboard too?

Hmmm...I see what you mean about the stain showing through. Good thinking but the ceiling actually feels wet to the touch, and I'm almost certain it's a good bit larger than the old stain.

[wowfudge]

Right - it could be a very fine spray of water which is running down the back of a pipe/cable/bit of wood. If you've looked but couldn't see anything, try looking across a wider area and also try turning on taps, the shower, etc in the bathroom as it could be water being drawn through a pipe rather than sitting in one if it's a very small leak.

[fiorentina]

We have had the scenario that the window sealant at the top wasn't properly sealed. The water from heavy rain came in and travelled along the beam and then out the light fitting. Could it be something similar?

[EcclefechanTart]

I am resurrecting this thread because I still need your help!

The patch is still there, in fact it seems wetter and has spread slightly. But I am absolutely flummoxed as to the cause. In the bedroom above, I have been under every floorboard anywhere near the damp patch, and there are no pipes, and everything is dry under the boards. I can see the backs of the laths and they all feel bone dry.

The radiator pipes are about 5 floorboards over, and they run the opposite direction (and also seem bone dry). The patch is nowhere near a window. It basically extends across the width between two joists, is wettest right in the middle, and doesn't spread beyond the joist at either side. The joists themselves felt complete dry when I took the floorboard up in the room above. There is nothing else under the floorboard.

What the hell can it be?? I don't even know what kind of professional I should call to look at it. If it were a leaking pipe, I would call a plumber, but I don't think it is that. I am at an utter loss.

[EcclefechanTart]

It's not possible, is it, that we spilt something there months ago, and that it's dried in the bedroom and under the floorboards, but has stayed wet on the actual ceiling down below?? I am scraping the barrel of ideas now.

[capsium]

Could you put a large piece of coloured sugar paper over the area, under the floorboards? This would mark with any flow of water and you can then work OT which direction it is coming from.

[capsium]

Out not OT. Typo.

[EcclefechanTart]

That's a good idea. I will put paper down there tomorrow morning. I can't imagine it will get wet though! Everything under the boards was so dry.

[TheCountessofFitzdotterel]

I suppose if there was any reason the patch was colder than the surrounding ceiling then it could be the air condensing on it? That's no help though as the only reason I can think of for a random cold patch in the middle of the ceiling is a ghost.

[MisForMumNotMaid]

You mention in your initial post that there are wires above the damp patch. Any chance that moisture could be tracking down the wires and the low point in the wires is above the patch?

We had a slight drip from our bath and a stain on the kitchen ceiling below. Ours was more of a pool of water as it turned out. I drilled a tiny hole in the middle of the damp patch to allow the moisture to trickle out before filling a month or year later and repainting.

What about putting a small light dish like a plastic lid above the damp patch but below the floorboards ideally with something like a piece of newspaper in (the ink will smudge if it gets damp) where as tiny amounts of water might just evaporate before you see them.

[pestilence13610]

Follow those two joists to the edge of the room, nay all the way to the external walls. If those joists meet another one, follow it too sooner or later you will meet a pipe. Water sneaks around under things, the leak can be at the other side of the house.

[EcclefechanTart]

Thanks for the suggestions! I will try both newspaper in a dish, and sugar paper, in the morning.

I felt the wires (well the plastic cable, rather) and it felt dry and was covered in dust, so I don't think water can be running along it.

If the water were coming along the joists from a pipe, wouldn't the joist itself feel wet? They were both dry. (And - this is what I'm really mystified by - why would it choose that particular spot to make damp?)

[PigletJohn]

has the L&P ceiling been overboarded? Water can run on top of the plasterboard underneath the L&P.

In the middle of the wet patch, poke a skewer through the plaster so water can run out. Put a bucket under it.

[pestilence13610]

That spot must be a tad lower than other spots.