What could cause this damp patch?

[springmachine]

Weird damp patch on internal wall.

Showing up on both sides. Isn't coming from ceiling and doesn't come up form floor.

This photo was taken a year ago.

The damp comes and goes and with a dehumidifier running isn't too bad, but if the dehumidifier is off for a few weeks it comes back.

Any ideas?

(Damp specialist cafe round and told me it was rising damp and the house needed tanking)

Does the patch reappear when it rains or after? Are there any pipes in the wall? What's outside, above that wall?

I've been told no pipes are in the wall

Above is bedroom and bathroom - no plumbing work on the wall above though.

I've had roofer out to check roof and chimney and he says all is ok and if it was water penetration from roof I would see damp upstairs.

you say it's an internal wall, so it isn't penetrating damp.

Show us a pic of the other side please.

How old is the house, and what was it used for before it was a house?

What caused you to have it replastered?

How thick is the wall?

Is there, or has there ever been, a bathroom or kitchen in either of the rooms?

Who told you there are no pipes in the wall, and why do you believe them?

Have you looked under the bath above? Is there a shower, or radiator or something on the wall upstairs?

Beware of rising damp treatments salespeople! There is a school of thought that rising damp is a con. Anyway, rising damp, if it does exist, generally doesn't rise much more than 1.5 metres apparently, the damp there looks much higher?

Do you have a concrete floor OP? We had very similar damp caused by a leak in a pipe buried under a concrete floor. We were fortunately able to cap the pipe off at each end and run it in the ceiling instead.

@user1484830599 funny you should say that. At the time the damp patch appeared we had a leaky mains pipe under the concrete floor on this side of the wall.

Or insurance company excavated it and it was capped and then dried out with industrial fans for 2 weeks.

@PigletJohn

Attached is a photo showing the other side of the wall which has been lining papered which you can see has bubbled in the same sort of area.

The wall was the original external wall of the 1900's house. The extension is a kitchen.

The thickness of the wall is shown in the second attached photo.

The reason it was replastered is the Kitchen was ripped out along with the tiles that left the walls very patchy

@phoebemac

A damp specialist had been around and told us the whole ground floor needed tanking and cement rendering after pointing his moisture meter at the walls.

Funny thing was the house had just had a mains water leak at the time so yes, thing were a bit wet, but other than this one weird patch, we've had no other damp issues and the walls have been skimmed and painted throughout when we moved in a year ago.

I'm very distrustful of damp specialists who have damp treatment to sell

When it was last plastered was the proper plaster used? We had a similar problem in a house as it’d been plastered with something called Carlite (I think) which absorbed any moisture in the air. Get a plasterer to take a look at it.

We ran a dehumidifier over winter which mostly kept any damp from reappearing but when it's off for any length of time it slowly creeps in.

I've had the roof checked, the gutters checked, and I've been next door and all is ok and water tight, maybe it is rising damp?

My only issue with that is I really disbelieve rising damp can occur in a house that's stood for 120 years without any prior issue.

A issue that's possibly only been around since a pipe spring a leak.

I've just had an idea - could it be that the wall had soaked up some moisture from the leaky pipe, the wall was then skimmed and didn't dry out enough, and then maybe it's just never quite dried out and any extra moisture from condensation in the air is attracted to this particular area?
Long shot !

Another long shot is that there is still a leak somewhere 😱
But we had everything tested and the mains were re-routed to solve the issue

@llangennith it was plastered this time last year, pretty standard basic skim coat as far as I know but no idea.

He's working on a family members house so I could get him to come back and take a look

I don't mind getting it hacked off and reskimmed if I can be sure it's not going to reappear again (I've been repainting over it periodically to make it appear occur)

U'd pull at least some of the plaster off, on both sides, to see what's behind it. I see now it used to be an external wall. The shape of the wet makes me think there is a forgotten old pipe with a slight leak. V ery common in an old house. More so if the room had previously been a kitchen, but if a bathroom is above it, water will be running up to it in some way, and might be dripping down. If there had previously been a fireplace, there could have been pipes between a back-boiler and a hot cylinder.

Otherwise, water might be running down inside the wall (less common).

Did you say it happens after rainy weather?

Have you got a water meter?

The height does not conform to rising damp, you can forget that.

@springmachine - just a thought, was it replastered with gypsum plaster? I have read that using gypsum plaster instead of lime in old buildings can cause damp issues. If you google you'll find some info.

ps

I can't work out the layout from the pics. I think the damp wall is 9" brick, formerly an external wall, and I think there is another wall perpendicular to it.

If there is a water pipe, it is probably in the internal corner, where it could easily be concealed.

There is a horizontal crease in the plaster on the inside, where something must have been - was it an old worktop? Or is there a cable or pipe behind it?

I see a thermostat on the wall, is that close to the damp patch?

Can you draw a plan of the ground and first floor, showing the position of the bathroom fittings, pipes and drains in relation to the wet patch, and where the roof for the extension meets the old house?

Rough floor plan just sketched out showing the damp wall and where it is located in comparison to where the mains pipes are

I realise I confused the location due to posting up the two later photos which were taken last night after it's all been decorated and a kitchen installed.

The initial picture was taken a year ago after removing old kitchen.

Attached is now what that same wall looks like close up. It's been painted but you can see some flaky fluffy paint coming off in a few patches

The grey painted wall is the lounge side of the room inside the original 1900's part on the wooden floor.

I think the reason this wall is showing a different shape of damp is because years ago someone else damp proofed the old part of the house up to 1m high and so the damp is just above it.

Then again, since the leak the skirting board on that particular wall has shrunk and cracked slightly. This has since stopped, but the section in that area does need replacing

That looks to me like that is moisture from the leaking pipe having been retained within the old external wall and not having been dried out properly (two weeks is not a long time to dehum a room for with very old thick walls).
I think you're going to need to strip the plaster off and dry the wall again properly - would be worth contacting the insurers and saying damp has recurred because of it not being dried properly and let them find the problem and sort it out

When you replaster you need to use lime which breathes. I'd say it's water trapped behind if there's definitely no pipe work.

@unadulterateddad

That's what I originally thought, surly after a year it would have gradually dried out through the plaster?

I would ask insurance to come and sort it again but I changed companies at renewal this year

Il get a pipe and cable locator just in case

I've been told there is definitely nothing in the wall, but who knows?!

I see the water pipe now goes upstairs in the extension, but before it was built, there must have been a pipe going upstairs in the old part of the house. mAnd ptobaly one running down to the original kitchen.

Before the extension was built, where was the kitchen sink?

Are you able to examine the concrete floor to see if it is dry?

Can you lift a floorboard in the old part of the house close to the wet wall?

Treating or tanking a wall doesn't cure damp, it just hides it.

The sink position in the extension remains in the same place as it is now

Itl be hard to check the concrete floor as the floor is laid but in the original house we've had it carpeted so it should be easy enough to pull that back and inspect he floor and underneath I assume?

yes, but also check the bottom of the walls round the room as the new floor will (should) have a DPM

Do you know where the kitchen sink used to be in 1910?