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)

Is there some sort of sump forming under this wall? Water getting into a “hole” under the house and tracking up the wall? Have you had cameras up the drains?

I am amazed that a boiler is damp. They are usually warm. I would also guess that the 70s extension wasn’t brilliantly built either. What water is being retained under the extension in the soil? I think a bit more actual digging and soil investigation needs to go on under the house and I would worry that there is another leak and the water is tracking back to the base of the wall. I think you need a qualified surveyor and not a salesman.

Ditto the comment about leaking pipe in a concrete floor - an old buried radiator pipe turned out to be the cause of a damp patch on the floor/wall in our living room.

I had an almost identical problem in a basement flat.

It was centred around the thermostat. We couldn’t work out where it was coming from until we talked to the lady upstairs (who was also our landlady). She had a new washing machine fitted in the kitchen which was almost above the damp.
The pipes hadn’t been fitted properly and the slow drip had worked it’s way along the brickwork until it got to where the wiring for the thermostat had been chased into the wall.
There it worked it’s way down the chasing until it reached solid brickwork again where it spread out.

Ive spent most of the recent weeks reading up on damp, rising damp, leaks, leak detection etc

After hardly getting a wink of sleep i feel like I have exhausted all online resources last night and feel more confused than ever. The information out there is so conflicting.

The facts as I know it:

1 - we had an under floor mains burst that leaked over a period of a few days causing a flood under the house approx 12 months ago which insurance dried out for just 3 weeks, didnt replaster and said it was fine and closed the claim.

2 - generally we have not had issues since other than this one patch of wall at approx 2m heigh not drying out.

3 - it does not smell

4 - it is not cold to the touch

5 - general hygrometer readings are now stable

6 - there is no mould appearing

7 - the damp has not spread in all that time the patch is the same size

8 - the wall is internal, and solid brick no cavity.

9 - i have had leak detection company round who confirm not a plumbing issue

10 - i have had a plumber round who says it is not a plumbing issue

11 - i even got a roofer round (just in case) to check flashing and any roofing defects and he says it is all sound

12 - damp proofing company thinks is rising damp and says that rising damp can go higher than 1.5m in the right circumstances

13 - neighbours house adjoining us is empty and dry

14 - this damp patch only appeared after the leak in the floor occured

15 - i have gone through photos from when we initially viewed the property in 2016 and there was no sign of damp on that wall on either side.

16 - the only time the house has smelled even slightly musty is the weeks when the floor was wet due to the leak

17 - reading online tells me in places that rising damp can rise up above 1.5m in some circumstances

18 - other online sites say it cant and is usually kept low at skirting board height

19 - a lot of websites done agree that rising damp even exists

20 - if it was rising damp wouldnt this have appeared a long time ago?

21 - it doesnt seem to be affected much by the weather, it was there in winter, its there now, its still there after all the storms this weekend and no more wet than it was a few weeks ago during the heatwave

22 - there are visible salty deposits, these brush off and reappear again once painted. if i brush them off on the non wallpapered side of the wall i can see the plaster underneath looks dry

23 - thermal imaging camera from yesterday showed that the wall was warm, no cold spots

So I am confused.

Do I continue to strip off the wall paper and plaster and assume that underneath the wall just needs to breath properly and once it is replastered the salts will stop attracting moisture to it?

Do I continue to be concerned that the wallpapered side of the wall is continuously mildly damp?

Could this be that its just holding onto the water and the salts are self perpetuating the issue?
Or is it that there is something else causing the wall paper to be wet?
Do I give in and give the job to the damp specialists that oh so want to inject my walls and tank it?

Of just slap some paint on it and move?

When it was joined to the extension could the flashing at the join be damaged?

@SimonBridges tempting! But we want to stay here medium term at least

@bionicnemonic extension was done in the 50's with later addition in 70's.
Roofer has checked flashings and all fine

Maybe 12 months isn't long enough for a thick solid wall to dry itself out after hefty mains leak 🧐

It hasn't had 12 months though because it has been re plastered for most of that time?

Nope I guess not. 12 months since the leak.
It was replastered approx 10-11 months ago

Forgot to mention - the plumber that cane out to do the leak detection charged me £144 an hour and took 1.5 hours and couldn't give me an answer at the end of it.

Having spoken to other people apparently that's a ridiculous amount.

Feeling a bit ripped off

if you're still getting salt efflorescence, it is still drying out.

pencil round the damp patches and photograph them so you can see if they're getting larger or smaller

If you set a household fan to blow against the wet wall (not a fanheater) it will evaporate the water off faster. You have to ventilate the room very well to get rid of the water vapour in the air. You will know it's working when the windows are no longer misty in the morning.

Any wallpaper should be stripped off as it will delay drying.

The wall should not be painted with vinyl emulsion, which will delay drying. Dulux Trade Supermatt is porous and is made for new damp plaster to dry out (it is not very durable but can be mixed in various colours. White and Magnolia are ready-mixed and cheapest.

As a rule of thumb, a brick wall is said to dry out at the rate of about one month per inch of thickness. This is usually walls that have been soaked by rain during build; if water is still soaking up from the floor it will continue until the floor is dry. Poor ventilation delays drying. Open doors and windows speed it. Heat is not the key.

"Do I give in and give the job to the damp specialists that oh so want to inject my walls and tank it?"

no

that doesn't stop the water, it just hides it for a bit.

You might consider taking the skirting boards off. If the water is coming up from the floor, as seems likely, then the wall will be damp behind them and may cause rot. Hacking the plaster off behind the skirting will allow some of the damp to dry out before it can rise so far up the wall. Plaster encourages damp to rise up by capillary action. Plain bricks and mortar slow it down at every joint. Skirting does not need plaster behind it.

I suppose to make it look better you could slosh some Supermatt onto the bare bricks, but bare is always better for drying.

Assuming there is no water still leaking below the wall, it could be that this wall just has not dried out. It was replastered way too early in my view. The damp may well be in the bricks and the salts leach from the bricks. If you look at new brickwork, you can sometimes see white salty deposits on external brickwork.

I think I would hack the plaster off and expose the bricks. You will get a much better idea of what the bricks are doing as the weather and human behaviour varies. You can monitor the bricks and test for damp. Human behaviour is more important than the weather. How the wall functions as as something that “breathes” should be monitored. Some plaster traps in damp from the bricks. If you take it off, you are giving the wall a better chance to recover. Many would suggest at least 6 months or even a year.

I would stop wasting money by getting all and sundry out to look. Monitor it yourself if you are certain there are no leaks from anywhere.

Some historic house surveyors do not agree about rising damp however a leaking pipe near a wall will cause damp! Part way up a wall, it may be the bricks as I have suggested.

I would also check how the extension joins with the house. Is it watertight everywhere? Is any brickwork letting in damp because it’s poorly aligned?

The roofing is fine but is there anything else external above that bit of wall? In our old house with a similar extension we've had water coming in around a window and through an air brick

@PigletJohn the damp mark on the wall paper hasn't got bigger or shrunk over the last 12 months but maybe the wallpaper is just holding onto it?
I say wallpaper, but it's lining paper that's been painted in farrow and ball.

The other side is plaster skim coat with kitchen white paint.

As it is a formally external Victorian wall it is about 250mm thick of solid brick no cavity.

Additional information I have found out -

The kitchen side painted white is where we replastered. Reason for replastering was to make good after the removal of tiles and wood chip paper from that side of the wall.

The grey lounge side had previously before our ownership been damp proofed up to 1.2m (about the level that the damp starts to appear)
This I guess explains why the patterns of damp appear slightly differently to each side of the wall.

The skirting board to the grey wall was original solid wood skirting which showed no sign of rot 12 months ago but started to shrink and crack. This has since stopped and is no longer shrinking or cracking further.

We were getting moisture on the windows until we were given a dehumidifier.

I started running this around September last year and since then there is no condensation.
I bought a hygrometer which I keep in the room next to the damp wall which stays steady between 45-55% even now when I'm only running the dehumidifier occaisionly.

I pulled up the carpet around the damp wall and inspected the floorboards - all look good and solid.

@BubblesBuddy

Thank you. This all makes perfect sense.

It's a thick wall with skim coat over old skin coats so probably not drying out well at all

The kitchen unit against one side of it probably isn't helping.

Although I am surprised the fillet panel against the wall hasn't blown by sucking up some of the moisture but it might just be such a tiny amount still left in wall ?

I found a photo that shows the lounge fully decorated and carpeted fresh and the kitchen with the industrial fans on. Meaning it hasn't actually dried fully by the time we decorated

have a look under the floorboards.

It seems the water is either coming from underneath, or an undiscovered leak above.

Or, if it is just a sodden wall drying out, taking off the wallpaper and skirtings will help.

removing the plaster would help more, and you may see where the water is coming from, but is more drastic.