Chimney breast and damp??

[pieman]

Hi all,

I am after some advice if I may?

We live in an 1877 detached house. We are currently refurbing reinstating many of the Victorian features discarded during the glorious 70's.
We have had every room replastered. I have now noticed on one of our upstairs chimney breasts in a bedroom that there are damp patches appearing on one side of the breast. We last year opened up the fireplace and replaced with a cast iron fire surround etc, I doudt the damp is coming from the roof as the lead flashing around the chimneys was renewed about 2 months ago and the tiles are sound.
The chimney is lined as there is a log burning stove in the dining room below. There used to be a solid fuel boiler that used to be situated where this is, but taken out about 6 years ago.
I recently had a building inspector around and mentioned this to him. He thinks it could be the soot from the chimney has made its way through possible cracks in the chimney lining and is now causing this damp by attracting moisture.
Is this a possibility??
With regards to getting this remidied what are my options. During dry weather the walls appear to dry, would rain coming down the chimney pots cause problems. should I put a cowling on them. Or is there some kind of treatment that can be done internally to fix the problem?
It is only affecting the upstairs breasts to varying degrees, and only on one side, the side that then in the loft is angles toward the centre of the roof, if that makes sense!

Any advice greatly received, many thanks.

Simon.

 

[Goodboy]

It does sound like a 'salt damp' problem whereby the long term burning of fossil fuels has caused deposits of hygroscopic salts to build up in the flue and brickwork and over many years slowly pass to the surface. The hygroscopic nature of the salts (chloride/nitrate, possibly with ammonium salts) will absorb atmospheric moisture depending on environmental conditions, the greater the contamination the greater the water absorbtion - in more extreme cases this will lead to visual dampness but this will depend on the particular finish to some extent. Typically the dampness appears to come and go. (Frequently the finish will actually taste 'salty' but don't let the wife see you lick the surface - she'll think you are totally off your trolly!!)

Rain penetration will usually causes some degree of efflorescent salts deposits to form.

Thoughts:

I have known people to apply epoxy to the affected surface and then decorate over that, effectivly forming a barrier between the contamination and any new finish.

Dry line with suitable material but don't use dot and dab on basic plasterboard - salts may eventually diffuse through in the longer term leaving little damp/stained patches.

Hack the offending materials off and replaster: unfortunately if lime or similar permeable materials are used then some diffusion may occur over a period of time into this from underlying contamination - this is a possibility - and lead to future spoiling.

Just some thoughts if the problem is one of hygroscopicity

 

[Penners]

I doubt the damp is coming from the roof as the lead flashing around the chimneys was renewed about 2 months ago

Hmmm - when did you notice the damp patches? Where they there before the new flashing job was done?

Even the best builders can make mistakes.

Alteratively - if the chimney is lined, are you certain the top of the flue liner is properly finished to the top of the chimney? If rain was getting down in between the liner and the chimney, this could eventually seep through the chimney wall - particularly if it's in a pretty unventilated void.