Damp patches on chimney breast sides AND the adjacent walls

[Chelle21]

Hi, thoughts on this please ?

We have an Edwardian house (1908), with an open fire place which hasn't been used in over 15 years. The walls on either side of the fireplace are damp from the floor up to about a meter high, which we assume is where the connecting chimney pots were filled in with cement at some point and therefore allowing no air flow.

When we discovered this we obviously had the chimney stack repointed (lime Mortar), broken bricks replaced, removed all the old cracked flaunching and had new flaunching and new pots with new (airflow) caps fitted. The chimney was swept and cleaned. This was one year ago.

Internally, the fire place still has damp either side (we are assuming this will take an age to dry out properly, and perhaps we should start using the fire to support the drying process ?), but the adjacent walls also have large damp patches, also about a meter high in a square shape with hygroscopic salts appearing through the paint.

Can the damp from the chimney walls spread right across to adjacent walls ? or is the damp on the adjacent walls due to another problem ?

We are thinking about having the plaster removed internally in case it has been patched up with the wrong type (the rest of the internal walls are Lath & Plaster), if the wrong plaster has been used could this be causing external damp to soak in and appear on the inside ? does Lath & plaster stop this happening ? or.....

are we completely barking up the wrong tree and it is fireplace damp spreading ?

The entire wall with the chimney stack and damp problems is an external wall facing onto a large, wide open driveway.

Any thoughts much appreciated. x

 

[Cubist]

Hi Chelle and welcome,
Has the room been heated for any considerable time and is it well ventilated? Water penetration into chimneys may take a very long time to dry out due to their mass. Internal wall plaster, by the nature of the material, will draw damp out of the underlying brickwork and it will appear to spread across the surface to significant extents. Given the work you have already done I would suggest, if you are convinced and happy that no more water is getting into the chimney, to get some heat into the room on a regular basis, make sure the ventilation is adequate and perhaps consider using a dehumidifier to to accelerate the drying process.
Hope this helps and you can look forward to more advice/suggestions from others here who have direct experience of the problem you're seeing.
Cheers and good luck,
Cubist

 

[Chelle21]

Awesome ! Thank you so much for your reply. There is a small radiator in the room but (particularly this winter !) we’ve tried not have the heating on too much as it’s a big house and is costing us a small fortune ! This is why we wanted to start using the fire a bit more (it’s a small 3rd reception room so only gets used occasionally). We’ll get the chimney sweep in then to check it’s all good to use and see if that helps, thanks.
I’ll also invest in a de humidifier as the windows are double glazed with no air vents, so our guess is this is not good for an old house either !

 

[88v8]

The walls on either side of the fireplace are damp from the floor up to about a meter high, which we assume is where the connecting chimney pots were filled in with cement at some point and therefore allowing no air flow.

The stack... how many flues ?

You are referring to one downstairs room but were there were other flues that are now blocked?

If there are closed flues with no through-flow of air they will be damp due to condensation, and need the fireplaces reinstating or at the very least air vents at the bottom in addition to the ventilation caps on the pots. Each flue must be ventilated top to bottom.

Regards drying out, the rule of thumb is one month per inch thickness, after the source of damp is removed.

If the damp is trapped behind paint it will spread sideways. Had the walls been papered you would have a smaller damp patch with the paper peeling off. The contaminated plaster will need to be removed, and replaced with lime plaster which may eventually be coated with something permeable such as limewash or clay paint.

All a bit of a pain.. bodges of the past...

 

[Chelle21]

The stack... how many flues ?
A: 4 flues

You are referring to one downstairs room but were there were other flues that are now blocked?
A: Yep only one downstairs room has an open fireplace - everything else (2 x bedrooms & further downstairs room) has been blocked up - they also suffer with damp patches on the walls.

If there are closed flues with no through-flow of air they will be damp due to condensation, and need the fireplaces reinstating or at the very least air vents at the bottom in addition to the ventilation caps on the pots. Each flue must be ventilated top to bottom.
A: OK - yep we'll do extra air vents

Regards drying out, the rule of thumb is one month per inch thickness, after the source of damp is removed.

If the damp is trapped behind paint it will spread sideways. Had the walls been papered you would have a smaller damp patch with the paper peeling off. The contaminated plaster will need to be removed, and replaced with lime plaster which may eventually be coated with something permeable such as limewash or clay paint.
A: Thank you ! that's what we were thinking we should do but needed some reassurance.
All a bit of a pain.. bodges of the past...A :yep - all makes perfect sense and we are quickly realising 'bodges of the past' have definitely visited our house on several occasions !

 

[malcolm]

Photos please! A good vented chimney cap is the most important thing. I had a chimney that was blocked off at the bottom and covered by a paving slab at the top. There was a tree growing out of it. Put a tile under one side of the paving slab and the tree died. I'm sure the vent on top of the chimney is more important than air vents into the chimney. What do you have there? It's got to be water getting in.