Damp On Chimney

[Hel92]

Hi All

I’m looking for some advice, we have just bought a semi detached 1940s house and we have 2 chimney breasts in the living/dining area (adjoining wall) that have damp patches.

The previous owners had a damp course in 2012 across the whole wall but the guarantee is void due to only have a photocopy and the company now ceased.

We did have a HB survey which mentioned that it could be down to the 2 chimney pots that are open, there is also a lot of moss growing on the chimney. The worst damp patch pictured is on the back breast that has been closed up but has a vent fitted at the bottom. It has also spread to the alcove wall.

Could open pots be the cause of this or could there be a bigger issue?

 

[blup]

Looks more like rising damp from a bridged dpc, assuming the picture shows the side of the closed off flue. The vent and open pots would normally allow ventilation and therefore mitigate the impact of damp rather than causing it.

 

[Hel92]

Thanks!

Yes that is the side of the closed off flue with vent. What could cause a DPC to become bridged within that location with it being an internal wall with sub floor? Its been injected along the whole wall so does that mean we would need to get it redone?

 

[ree]

OP,
You show a stack with four pots on your side therefore there are four fireplaces - perhaps two on the ground floor, and two in FF bedrooms?
Which fireplaces are blocked off, and is one still in use?
The nearest cowl is a venting cowl, the next pot is open, the third is a metal gas venting cowl, the last pot is open.
Is the gas cowl attached to a flex flue liner?

The stack flaunching & the top courses will need rebuilding - work would have to be done in agreement with your neighbor.
Pics are needed to show more of the roof and the condition of the flashing.

The damaged decorated surfaces are possibly Hygroscopic chemicals coming through from the fireplace and flue?
Remove the skirting board & hack off all plaster back to brickwork - go about 500mm beyond signs of damage. Make good with a sand & NH lime 3:1 render mix,
dont use any gypsum.

The floor boards appear to be affected - go under the floor or lift a couple of boards to inspect.
GF Chimney breast & hearth joist trimming is sometimes found to be damp rotted?
Alcoves either side of the c/b's are well known for joist rot.
Pics of your fireplaces & hearths might help?
So would sweeping all the flues once the pots are secure.

 

[blup]

Thanks!

Yes that is the side of the closed off flue with vent. What could cause a DPC to become bridged within that location with it being an internal wall with sub floor? Its been injected along the whole wall so does that mean we would need to get it redone?

The outside of the wall might be higher than the dpc, thereby bridging it. Or the sub hearth might have allowed damp to rise, again because it is above the dpc (on the inside). An injected dpc would not counter that.

 

[Hel92]

OP,
You show a stack with four pots on your side therefore there are four fireplaces - perhaps two on the ground floor, and two in FF bedrooms?
Which fireplaces are blocked off, and is one still in use?
The nearest cowl is a venting cowl, the next pot is open, the third is a metal gas venting cowl, the last pot is open.
Is the gas cowl attached to a flex flue liner?

The stack flaunching & the top courses will need rebuilding - work would have to be done in agreement with your neighbor.
Pics are needed to show more of the roof and the condition of the flashing.

The damaged decorated surfaces are possibly Hygroscopic chemicals coming through from the fireplace and flue?
Remove the skirting board & hack off all plaster back to brickwork - go about 500mm beyond signs of damage. Make good with a sand & NH lime 3:1 render mix,
dont use any gypsum.

The floor boards appear to be affected - go under the floor or lift a couple of boards to inspect.
GF Chimney breast & hearth joist trimming is sometimes found to be damp rotted?
Alcoves either side of the c/b's are well known for joist rot.
Pics of your fireplaces & hearths might help?
So would sweeping all the flues once the pots are secure.

@ree Thanks so much for your reply!

Yes there looks to have been fireplaces in the 2 FF bedrooms however these have been closed up with no vent but no visible signs of damp upstairs. The GF dining room chimney to the rear of the house is the image attached that has been blocked off with a vent at the base which is the worst affected. I’m not sure if there is a flex flue liner attached to the cowl could this cause issues?

The front GF chimney is open but not sure if it was used. Both GF fireplaces have cement hearths pictured. Will try to get a pic of the flashing and roof

Thank you

 

[ree]

OP,
Has next door complained of damp?
It would help if you could positively identify which fireplace goes with which chimney pot? Some of what you say doesn't seem to match up with what I can see?
A flex liner wont allow flue sweeping. All your four flues probably need sweeping.

If you stand back for context then pics of the FF c/breasts might help?

The GF hearths will be sitting on soil surrounded by a fender wall - wood rot might be taking place. At some stage, if possible, you will need to crawl & investigate all the joists under the floor.
Remove & examine all the skirting boards that show the slightest signs of damage.
Are any gas restrictor elbows present at any C/B?

 

[foxhole]

Chimneys need capping , they allow more rain than simple ventilation can cope with .Remember there used too be heat rising daily from fireplace keeping things dry .
Any damp proof work would have been pointless and fruitless as you have found.

 

[mrrusty]

Of course open unused chimneys cause damp. Stick a bucket or container outside and see how it fills up in the rain - that's how much water is going down the open chimney, As to the issue of salts read this - I 100% concur with this article. https://www.tracebasementsystems.co.uk/post/damp-chimney-breasts