Damp patches emanating from sides of chimney brest.

[Edward90]

Hello everyone,

Please accept my apologies on this post as I am not very clued up on the correct terms for things but I will try my best to describe my issue.

I am currently experiencing small damp patches emanating from the sides of 1 of my 2 chimney breasts on the ground floor of my victorian 2 bedroom end terrace. The patches are each side of the chimney breast where it meets the wall. I have drawn a diagram showing this which I will add to this post. Top down view and looking straight at it view. They chimney breast itself feels like solid brick that has been plastered. The surrounding walls feel hollow plasterboard (although this wall still goes to the outside) I have been told these walls are 9 inch solid brick. This chimney breast has been bricked up at some point not sure how long for. No vent has been added upstairs or downstairs but both fireplaces have been bricked up. Neither can I see any vents or air bricks on the outside wall. Could this be the cause of the damp patches inside? Should I add vents to these blocked up fireplaces? If so is it possible to add the vents to the outside wall so I can avoid drilling the inside (Do to not wanting to damage the decorating) I have heard drilling holes into the bricks will be adequate as ventilation and then covering with a vent plate. Would this likely solve the damp patches issue I am having? and does it matter if I dill the outside wall so the vent is to the outside? Or any other ideas would help me massively. There is no leaking guttering or anything on the wall outside it seems pretty dry. Only water it gets is rain, although the patches do get darker when it rains.

Thank you

 

[mrrusty]

First, I assume there is not an open chimney pot! - if so, get it capped first. I have a similar issue which I know 100% is hygroscopic salts in the brickwork caused by burning coal. The combustion products react with lime and create salts which lurk in the brickwork. They absorb moisture from the air (hence show up when it rains and reduce when it is dry). Mine also show up about 1m or so up the wall. I don't think there is a quick fix. I have considered stripping back and rendering in SBR before replastering, or even replacing the salt loaded bricks, but for now I just dust off the efflorescence and repaint.

In the days when the chimney was used, of course, the constant heating kept the issue at bay.

https://www.heritage-house.org/damp...-have-i-got/salt-damage-in-old-buildings.html

 

[ted456]

Can you post pics showing the whole gable wall and stack and the base of the gable wall?
Is the gable rendered?

From either the interior or the exterior the best thing to do is open up all your flues at the fireplaces and sweep and smoke test them all. Remove all debris.
Then, as you make good, have vents/air bricks installed to through vent the flues.
Flue terminals suitable for redundant flues should be used in the stack pots.

The stained areas of thee c/breast cheeks need hacking off, and making good with lime render.
The stained plasterboard can be cut out - then the wall behind the D&D can be examined.
If the gap and wall behind the D&D is OK then make good with neat squares of p/board.