What’s causing this damp?!

[Holls81]

We have a real head scratcher.

There’s a small patch of paint that peels off in the top corner of our chimney breast. (Original patch was a couple of cm.)
(downstairs in the lounge.)

I sanded the paint round the area right back to where it stops flaking off.

The plaster underneath looks darker and the metal beading down the edge is rusty in a small patch.

Now, we asked a roofer to check the flashing and he said that if it was a problem with the flashing then the problem would also be evident upstairs (which it doesn’t seem to be.)
Structural engineer came out for something else and while he was here I asked his opinion. He too had no idea other than that it could possible be a flashing issue.

We’ve had a lot of rain over the past couple of weeks and the patch doesn’t seem to have changed (ie looking wetter or drier.)

when I sanded the area, down the side in a small gap in between the cupboard and the side of the chimney breast, some wall paper came off which seemed a little damp but not mouldy. (This is not a cavity wall)

Is it possible that condensation could be causing it where the air can’t get in to the little gap and the wet wall paper, that has seemingly always been in there (we’ve lived here 10 years and haven’t ever had wallpaper) might have been holding the water and not allowing the plaster around it to dry?

I’ve heard @pigletjohn might be able
to shed some light?!

not sure what else to try!

*I should also add that the dark patch on the plaster is my greasy finger print from the other day 😫

Is each flue vented top and bottom?

I can't see the fireplace. Is it bricked up in either room?

Does the room above contain water, such as a shower or radiator?

Does the chimney look damp in the loft?

You don't drape wet washing indoors, do you?

Thanks for getting back to me @PigletJohn

It’s a working fireplace with a log burner and a lined flue.

The room above is my daughter’s bedroom and the fireplace is not bricked up. (It’s not used though)
She has a radiator in her room but not above where the damp is.

we have a loft room and the chimney is behind the plaster board so we can’t see it.

we have a dehumidifier for when I have to dry washing indoors but i very rarely do. (Especially in the summer.) (If I do, it goes in the smallest bedroom with the dehumidifier on and the door shut.

Ive been taking photos daily of the patch to see if they get lighter or darker when it rains etc and it doesn’t seem to change too much. However, last Sunday we had a roast dinner and the wall went much darker and I think it must have been due to the condensation as it felt wet to touch and then lightened up again by the morning. I’ll send you a better photo of the corner edge and the little gap between the cupboard and the side of the chimney breast.

Tape a piece of clear plastic or clingfilm tightly to the wall.

If water forms behind the plastic, it is coming from the wall.

If on the room side, it is condensation.

What a great idea. Thank you.

If we continue to not be able to find the source, how do I go about painting it?! Do let really want to leave it like this!

If the galvanised metal corner bead has gone rusty, your water problem is bad enough that it needs fixing, not hiding.

What is in the cupboard? Can you take it down?

What is on the other side of the wall?

How far away are your Gaggia machine and your tropical fishtank?

The cupboard just covers the electricity meter. My husband is taking it off the wall today to have a look. There is no back to the cupboard and the wall inside it looks good with no signs of damp.

If we’ve asked a roofer and a structural engineer with no answers, who would you suggest next?!

Honestly, it’s driving me mad so I really appreciate that you’re taking the time to answer. 🙂

The other side of the wall is just our outside wall.
It is rendered with a small crack but that’s way lower than the wet patch. The engineer said he very much doubted that that would be anything to do with the damp bit.

I have something very similar on my chimney breast on the place I’ve recently purchased. We had a specialist heritage damp survey done - and were told it’s not the roof or any kind of leak but hygroscopic salts that have ‘infected’ the brickwork. They suck in water from the air so look worse when humidity in the room is higher.
The previous owners had tried replastering but it started to show through quite quickly.
I sanded back the plaster, used a dehumidifier for a month and then treated the walls with a salt inhibitor- very smelly!
Once that dried out I used a Zinsser sealer and primer and have painted over with matt emulsion. It’s not come back but it’s only been a few weeks.
In the long run we might need to do something more drastic but as it’s only a patch and apparently not causing any structural issues I’m trying the quicker fix!
I found this link quite useful:
https://surveyor.tips/understanding-salts/

@Karmatime thanks for your reply. Is yours in a similar place to mine? The plaster defo does look worse when we’ve cooked or something but it constantly looks darker than dry plaster. Doesn’t feel wet to the touch but maybe a little cold.
I’m just in a quandary with what to do.
obviously I don’t want to live with a bare patch of plaster in the living room but not sure which trade to ask next.
it’s so frustrating.
we have an old cottage and have had a couple of walls tanked over the last ten years since we’ve had the house and wondering whether that might be an idea.
I know it would then stop the water from getting in to the house but I don’t like the idea that it’s still getting in somewhere!
will it do damage to the brick etc?!
so many questions and I’m not sure who can answer them for me!

I have often heard hygroscopic salts talked about, but never seen them myself.

The colour of the plaster, and the galvanised beading, show that the chimneybreast was replastered in fairly modern times. I suppose there might be residues from old coal or gas fires soaked into the brickwork.

How old is the house?

Hi @PigletJohn
We had the chimney breast re plastered about 7 years ago as it was damp in places. The guy said he was going to damp proof it but tbh I think he was a cowboy. Couldnt get hold of him afterwards 🤬
we redecorated after a few weeks but the plaster on the area in question seemed to take ages to dry out. Every few months or so after we’d painted, I’d see a tiny little line, like a water mark but wondered if it was just still drying out. it wasn’t til we re decorated with a different paint that the paint all peeled off back to the plaster.
The wood burner was already in when we bought the house but we got the chimney lined for the burner at the same time that we had the chimney breast replastered.
(completely different company- this time with a certificate and lots of recommendations!)

Aha

So there was a source of damp that remains.

@PigletJohn oooh do tell!
you’ll have to explain it to me like I’m a child! Do you mean you think it’s been coming in externally all this time and still remains?

How old is the house?

Do you think there might once have been a back boiler, with pipes in the chimneybreast heating a cylinder above?

How old is the house? It's important as old houses need to breathe.

Tanking suggests damp issues in the past?

Also gypsum plaster has been used?

What's the render outside- cement or lime based?

Is the render painted?

I have seen old lime pebbledash that comes loose and holds rainwater in a pocket.

Another possibility is that water is running down the flue

If you can't see the chimneybreast in the loft (I think you may have to) take up a floorboard upstairs and look at the brickwork for signs of damp, and in the void for plumbing.

Or did it take a while to dry because of condensation?! 🤷‍♀️

*goes out to buy some clingfilm
to stick to the wall 😂

Why don't you want to tell us how old the house is?

It’s rendered then has something called tyrolean (I think) over it. Was like it when we bought it.
House is 1880

Sorry missed that! And completely missed the other poster ask it too.

1880 (this part anyway)

@SquishyGloopyBum
thanks for replying.

House is 1880

we had a couple of the walls damp proofed (rising damp we think)

what’s gypsum plaster please?

Not sure about the render to be honest.
we looked at having it redone recently and the guy said it’s render then covered with something called tyrolean (I think) 😫🤷‍♀️

Stone or brick?

Have a good look at the outside wall in case there in an old bracket fir a washing line or something that might have created a defect, and see if the chimney is well bonded into the wall with no gaps or movement.

See if a cable goes through the wall.

Go out with an umbrella on a rainy day and see if water runs down the wall.

Gypsum plaster is a modern plaster made from gypsum. Old houses would have had lime based plaster which was breathable.

Rising damp is actually very uncommon and tanking is quite an invasive measure.

I think you need to go back to basics and get a specialist surveyor who knows historic buildings. They need to look at the whole house.

Don't keep throwing good money after bad. Your interventions such as plastering and tanking may make things worse.

@SquishyGloopyBum oh gosh! I hate the fact that we may have made the house worse 😫
will the damp proofing that’s been done have damaged my home?
We had a preservation company come round and they suggested the damp proofing round the bottom of the walls as the walls were
extremely damp at the bottom (on the damp reader.)
The problem I have, (and I don’t think I’m alone in this) is that I don’t know about buildings or their problems That’s why I pay a company or tradesperson.l should I need a service. The thing that I find really frustrating is that everyone tells me something different 🥲😫

Many "damp experts" are in the business of selling silicone injections.

They will not repair any of the faults that cause damp.