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Chimneys & Fireplaces

Damp on 1st floor bedroom chimney breast wall

I live in a 1958 detached 3 bedroom centrally heated brick house with radiators. The chimney is on the side of the house which is about 10' away from the house adjacent & doesn't get any direct rain on it. The chimney is built on the outside of the original house wall and therefore the walls behind it inside the house are flat (flush). I suffered with problems of damp in the chimney with a leaking stack and so when I got new roof tiles I had the chimney taken off at loft height. The chimney had been a real open fire and I had it swept by a professional chimney sweep. The top of the chimney is open in the loft and sealed from the weather. The bottom of the chimney in my lounge has a decorative only gas fire which has a permanent open vent. I then installed a further 2 airbricks on the outside chinmey wall (one at the top & one at the bottom) which has the original DPC at the bottom.
Despite all of this and experimenting covering (capping) and uncovering the top of the chimney stack inside the loft to increase/reduce airflow I am still getting damp readings (over 44% on damp meter) on my plaster in the 1st floor bedroom on the wall immediately behind where the chimney stack goes up on the outside just below ceiling height and about 1' from floor height. When I have inspected inside the chimney (by looking down from inside the loft) I get these same readings on my house chimney wall nearest to me and the mortar, but not on the side walls or outer wall of the chimney.
The 1st floor bedroom is well ventilated (windows always open).
When I leave the window closed with the room radiator on with the dehumidifier switched on the levels start to fall.
Any ideas guys how I solve this issue it's really puzzling me ?

Ok so since asking the initial question I have removed the plaster off the wall back to the brick. The bricks behind and the mortar show high levels on the damp meter as mentioned and yet to the left and right of the chimney this is fine ?
Would it be worth me having my exterior chimney removed ?

3 Answers from MyBuilder Chimney & Fireplace Specialists

I had same problems on my own home. We tried everything. In the end we had to take the chimney stack out all the way to floor level on the 1st floor, noticed a crack in the brick work. Fixed that And then dpc, batons and damp resistant plaster board. That was 3 years ago and still no signs of damp


Answered 10th Oct 2018

Try putting brick air vents opposite each other on sides of the stack so the air can flow through


Answered 11th Oct 2018

Maybe a little late with thsi but there is a phenomonon caused by tar from unburn material, or using underseasoned timber, leechingv through the chimney structure and depositing salts on the surface. These salts then absorb moisture actually created within the room and presents it back as dampness. This process is called deliquescence.
Desalination of the plaster is needed or replacement of the plaster may be the most expedient route as well as desalination of the brickwork to reduce the chances of it happening in the future.


Answered 13th Aug 2019

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