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)

Unfortunatley no idea about the location back then. I've been in neighbours houses with older kitchens but the kitchens were still on the rear extensions.
I assume at some point a kitchen might have been in the actual old part of the house?

Would a house this age have dpc?

very likely to have had a slate DPC, two bricks higher than the ground level was when the house was built.

Might still be visible near the front door.

If you can find airbricks, it might be on top of them.

Ok.... I have been busy making further investigations.

What I have found out is that above the damp wall is the bathroom where the boiler is. The pipes from the boiler bend within this wall on the upper floors to feed the radiators to the upstairs bedrooms.

Where I could see the pipes enter the wall there is no sign of leak, but I couldnt get further in to see if there is any possible leak to where the pipes bend.

Possibility maybe?

The boiler since we lived here is 10 year old cheap baxi that has been on the blink and we have a plumber who has come a few times to replace parts.

We want to extend so have it in the plan to replace the boiler for something suitable when the additional bathroom is installed and therefore putting up with having to reset the current boiler on a regular basis.

It loses pressure approximately once every month enough for it to need topping up and resetting, and also has a fault where it 'kettles' when running the hot water for any length of time.

Ive contacted a few more damp specialists and surveyors.

The surveyor wanted a few hundred pounds for basic survey.
The damp specialist I chose to call was one specialising in heritage properties and using breathable solutions.
I had high hopes, but when I explained what was happening he was just talking about coming out to take the skirting off and remove the carpet to investigate the DPC, and also wanted to charge for the survey too.

I have a hygrometer that I keep on the floor next to the wall. Which is showing a current level of 56% humidity.

This fluctuates throughout the day depending on if Ive been cooking or if the windows have been opened, so not too sure its much to go on.
Generally its pretty stable though and apart from over winter, I havent had the dehumidifier on and there is no condensation appearing on any windows.

Not too sure if this gives much more of an insight @pigletjohn...

Im planning on getting the heating engineer out again and thinking about just getting him to replace the boiler as its problems are increasing with age, but this wont solve the leak if there is any ....

I'm no expert but a boiler that needs repressurising regularly indicates there is a probably a leak somewhere in the system. I'm willing to bet a leak on a pipe connected to the boiler is the source of the damp problem.

@wowfudge
This would explain why the damp patch wasn't visible when we viewed the house or when we initially moved in and only cropped up when we started using the heating.

Prior to that the boiler had not been switched on for around 2 years so was not under pressure ...

The fact there's a chemical damp course would explain why the damp is coming to the surface halfway up the wall. A tiny leak on a central heating system can cause loss of pressure over time. It's also likely to get progressively worse. Have you had the floorboards up upstairs to see where the boiler pipework is and if you can see signs of a leak?

Boiler man came out today to fix old boiler (needs to be replaced but that's another story)

He took a look at the damp patch and tried to inspect the pipes but couldn't see any sign of a leak above that wall.

I think we are going to try and strip back a bit further but we are still stumped

Insurance company are coming out to survey for repairing the damage to the walls but obviously we want the cause of the damp to be solved first so it doesn't happen again.

It's all making me a little be anxious that we don't seem to be getting anywhere with it

Hmm. Did the boiler man do anything re: the loss of pressure? Will be interesting to see if that is stopped by whatever he's done or it carries on happening.

He said that there were a few points on the boiler where water was escaping (so slightly that no puddles were forming)
That he said it could be the reason for the pressure loss.

Surely that water didn't just puddle and stay there? Presumably at least some of it evaporated then will have potentially condensed somewhere. It's been warm the last few days so I wonder if it less obvious where it might have been tracking? Plus warm air holds more moisture than cold.

Sorry - you've said no puddles, but it must have gone somewhere?

There is a part of the boiler that's wet to the touch, the drips have calcified and crusaded up and underneath is a ply board panel, where there is a slightly darker patch where I guess some drips have sunk into.

So it's a minor leak but not flooding (badly explaining myself)

A minor leak, especially over time, can cause the damp you've experienced. For calcification to have happened then it's been going on for a while. If you're in a hard water area, the minerals in the water will be bubbling through the plaster too.

Update further to recent investigations - leak detection company came out today.

Confirmed it's definitely not coming from any pipework. There are no leaks on the system other than the boiler itself which isn't causing any damp.

They came out with the damp meter which concerned me a little and it's red loft and beeps went crazy all over the wall (no surprise) but also over the bottoms of pretty much every wall on the ground floor.
He said we have damp.
This is strange as no other walls have any visible damp, it's not wet to the touch and there are no tide marks or shadows or even any musty smells in the house.
He started pulling back the carpet and said it smells damp under there.
I couldn't smell anything and it looked dry to me.

He then got his thermal imaging camera out and it showed cool spots at the bottom corners of the wall, but where the damp wall is it was red and as warm as all the other walls on the house.

That's where it stumped him.

He suggested that the plaster gets stripped, it gets left to dry out properly, and then replastered and decorated.

"damp meter which concerned me a little and it's red loft and beeps went crazy all over the wall (no surprise) but also over the bottoms of pretty much every wall on the ground floor"

The meter is a visual aid used by people who sell dampproofing to convince you that you need to spend some money. It is usually misleading.

I'm all in favour of pulling the plaster off. If there is a wet patch on the concrete floor on the inner part of the house, I'd still suspect a leak. Might be drains if there is some way of knowing it is not plumbing. Did they use a noise detector? You haven't got a water meter, have you?

If the wall has been treated against damp, and if the floor is concrete and has a dpm, the water may be visible where it can get out, not where the source is. That might be why it's soaking up into the bottom of the walls. With a wooden floor its easier to take some floorboards up and have a look, a sniff and a feel.

He didn't use a noise detector.

The concrete floor in the kitchen was visibly dry when the flooring went down.

He used his damp meter across the floor and said it was reading dry.

He did pull back the carpet in the old part of the house and pulled up floorboard which you could see the ground underneath which appeared dry.

There are air bricks front, rear and side.
They are clear and above ground.

He did say that the thermal camera made it appear that the wet wall was actually dry underneath and he thinks that the previous leak had caused hygroscopic sales in that wall and the wall should have been stripped bare to dry throughly back then.

He thinks if we strip it now and make sure there's nothing else untoward underneath that a fresh coat of plaster should stop anything reappearing.

He said the wall looks wet but there are salts that you brush off and underneath the plaster looks light pink and dry

The neighbours had had issues with drains not long after we had the original leak.

This was all sorted so drains are now clear on the row.

We have no water meter.

At one point his diagnosis was that the moisture was coming in through next door but I've been next door.
They are all stripped back to bare brick, no plaster wiring or plumbing or flooring and they are dry as a bone.

I had hoped hiring a leak detection company that he would have a noise detector.
He said he could pressure test the heating system but as the boiler is faulty it wouldn't make much difference.

When the original leak was found last year (the mains leak under the floor) it was found with a noise detector.

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 think as long as you declared the claim the new company should take the claim on.
Alternatively if the damp stems from the leaking pipe (which sounds likely) shouldn't the original company who did the repair come back?

The new company seem happy to take the claim on.
I'm now thinking the old company should come back and sort it.

It could have been so easy for them as at that time there was no kitchen installed, no carpets down and we hadn't decorated

One thing I am confused about in peticular is when the man held his damp meter up to the other living room walls. Walls which show no sign of being damp at all, don't feel cold or wet, have no flaky paint or any issues but we're high readings on his meter.

I said to him that they are visibly not damp and he said that they are as the damp meter says so.

How can that be?

it's a sales aid.