Damp patch on inside of chimney breast wall

[Mamabear256]

Hi everyone

In the colder weather/rain this damp patch appears on the bottom of this chimney breast wall. It stays there until summer when it’s hotter and it seems to then dry up and look a lot better. Last year when we noticed it we looked outside on the outside of the wall, some of the brickwork had gaps in it where cement should be. So my OH filled these gaps in with cement, however now the weathers cold and raining again the damp patches are back. There are 3 patches roughly this size. The one in the pic is on the chimney breast wall (it sticks out), and the 2 other patches are in each corner of the wall on the left hand side of the chimney breast wall right next to it. Does anyone know what it likely to be causing this?

Is it a working fireplace or has it been blocked up?

My parents had damp at the bottom of their chimney breast after they had the chimney blocked up. Apparently it was caused by poor ventilation in the chimney itself.

Just a cracked chimney pot can let plenty moisture in. Also, how is the guttering? Clogged gutter can cause water to pool and then soak the front of a building, and eventually it will penetrate and show as damp spots on interior walls.

Best to get a proper tradesman out to run their eye over the entire thing.

It was a working gas fireplace, although the lever broke on the fireplace last year so we haven’t used it in a year but it’s not blocked up

As pp said, blocked chimneys need ventilation fitted. It’s poor quality work if it’s not fitted and it’s easy and cheap to fit retrospectively

Ok, in that case, worth fixing and using

I wouldn't have thought not using it would be the issue? As the fireplace is still not blocked up, it’s still open. We’ve just not used it?

Also to PP - I am not really sure about the chimney and the condition it is in, or even the guttering. I think we’ll have to get someone in to have a look at that. I’m pretty clueless with this kind of stuff

If this isn't an exterior wall then it won't be guttering, but if there is damage to the mortar on the chimney stack, then it's also possible some of the bricks might need replaced. If the smooth face is lost from a brick then it will permit water ingress itself, not just through the gaps in the mortar between individual bricks.

If there are multiple patches of dampness at different heights on the same piece of wall, then it's not coming up from below, and as it's a chimney breast, it screams water ingress.

Sorry yes it’s an exterior wall

The damp patches are all at the same height, sitting right on top of the skirting boards in the corners of the wall

I’ve actually just noticed another patch on the other side of the fireplace too

How old is the house?

If it's pre-ww1 the chances are the cement has sealed in the moisture and is making the damp worse. Older properties were built using breathable materials in the pre-plastic age so lime mortar should have been used for repointing.

Either water is getting in or it can't get out.

The first implies something is wrong with the flashings or pointing on the chimney.

The latter is the classic using cement plaster instead of lime.

I had a longstanding damp patch on a chimney breast, solved almost immediately by repointing with lime plaster.

It could be the flashing round your chimney breast has come away. Get a roofer to have a look.

Can you see where the damp proof course is on the outside of the chimney wall? If you stick some pics up we might be able to see it and/ or work out of the gutters are leaking.

So we’ve hopefully got someone coming to look at it this week. Just waiting on a call back to arrange a time. The exterior part of the wall is on my neighbours side so I’ll have to ask them if I can go into their garden, I’ll try do that tomorrow.

Does anybody know if it is dangerous for children as I’ve got 2 young kids? I’ve heard of damp/mould being bad for breathing but I assume not at this level?

Now thinking about it it is always noticeable when it rains so I am thinking it must be something to do with water coming down the chimney. As I said before originally we thought it was the external wall bricks as there were gaps on the outside so water could get in last year, but we’ve cemented that up since and it’s come back now it’s started to rain again so I don’t think it’s that now. Unless it’s trapped water from that since then, but surely the damp patches would have still been there in the summer then, and not just appear when raining?

Thank you all so far for your responses!

It's not dangerous unless mould is growing on it. Generally black spots and I can't see any.

Be careful if the person who come round suggests injection damp proof course as they don't fix the actual cause of the issue and can make the situation worse.

Absolutely if they suggest damp proofing show them the door.

If it's always worse when it rains, it is probably the flashings.