Damp on Chimney Breast

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radgiegadgie

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Hi

I'm seeing damp issues on the chimney breast and external wall in the back bedroom of a mid errace victorian house. On the roof it seems like the flashing on the firewall and pots are the source of the water ingress and I'm seeing damage in the plaster and external wall as a result. If I sort the roof out (assuming thats root cause) what's the action for the internals? Any help appreciated it's all new to me!


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OP,
1. Why not post pics of the chimney stack and the suspect details you mentioned?
2. Have you been in the loft & investigated for leaks and damage?
Lift any insulation & check the ceiling from above.
3. Is it a shared stack?
4. Examine all your chimney breasts and fireplaces for water damage - are any fireplaces blocked off.

5. All flues should be swept clean and vented at bottom & top for thro ventilation.
6. All the damaged plaster should be removed back to brickwork & then rendered with a 3:1 mix of sand & NH lime - & skimmed with, say, Limelite finish. No gypsum plaster to be used.

Read up on the Similar threads below.
 
Chimney stack and firewall above the internal damp area and loft space
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ree said:
OP,
1. Why not post pics of the chimney stack and the suspect details you mentioned?
2. Have you been in the loft & investigated for leaks and damage?
Lift any insulation & check the ceiling from above.
3. Is it a shared stack?
4. Examine all your chimney breasts and fireplaces for water damage - are any fireplaces blocked off.

5. All flues should be swept clean and vented at bottom & top for thro ventilation.
6. All the damaged plaster should be removed back to brickwork & then rendered with a 3:1 mix of sand & NH lime - & skimmed with, say, Limelite finish. No gypsum plaster to be used.

Read up on the Similar threads below.
Click to expand...
Thank you for your detailed reply, I've added some photos of the roof, stack and the internal space from the loft access. It's a shared stack and non of the fireplaces are currently in use in the house.
 
OP,
Thanks for the new pics.
You say the: "fireplaces are currently" not in use - will they come back into use sooner than later or will they remain redundant?
Its probably best just to sweep all the flues and leave the fireplaces as they are.

The loft pic shows old & new water streaks on the party wall. It also shows some very damp looking rafters. Are there piles of insulation & building debris on the joists? Investigation in the loft is needed.

The stack will need to be worked on from both the neighbour's side, & yours.
For a proper job then all the render should be removed, & the brickwork examined.
Near the stack crown some of the brickwork needs replacing/rebuilding.
All the pots need resetting in fresh flaunching.
And, as mentioned above, the pots require ventilation cowls.

The stack flashing is a mess, & probably needs re-doing.
The what looks like one-piece sheet lead draped over the parapets seems to be working except its a bit short at the gutter.
There's a slight possibility that the first course of tiles is at a different plane to the rest of the tiles - if so its because the fascia wasn't fixed high enough.
The tiles might not reach far enough over the gutter & moisture is creeping past & staining the fascia and wall below.
 
Thank you for your detailed reply, quite a bit contributing to the damp problems and to work through from the top down. I'd not noticed the piles of wet lagging, and the damp rafters are a big concern too. Would they dry out and be safe if the roof is weather sealed?

As you say much investigation is needed!

I'd like to add a woodburner in the future but not at the moment - I have a few more pressing issues!
 
With regard to the internal finishes where the crustiness indicates salt contamination, have a read of this https://www.tracebasementsystems.co.uk/post/damp-chimney-breasts which I completely agree with. As an alternative remedy you can use plasterboard fixed with a non-water based adhesive (if you use wet dabs, the salts come through the dabs). You could use foam adhesive, or use top-hat metal battens https://www.siniat.co.uk/en-gb/prod...s/frame/dryliner/siniat-shallow-wall-channel/ The result, whatever you do, is to isolate the surface finish from salt-poisoned bricks behind. I have found drylining using plasterboard is a successful solution and an alternative to isolation membranes.

If you just strip and replaster, the salts may well (will probably) show up again
 
mrrusty said:
With regard to the internal finishes where the crustiness indicates salt contamination, have a read of this https://www.tracebasementsystems.co.uk/post/damp-chimney-breasts which I completely agree with. As an alternative remedy you can use plasterboard fixed with a non-water based adhesive (if you use wet dabs, the salts come through the dabs). You could use foam adhesive, or use top-hat metal battens https://www.siniat.co.uk/en-gb/prod...s/frame/dryliner/siniat-shallow-wall-channel/ The result, whatever you do, is to isolate the surface finish from salt-poisoned bricks behind. I have found drylining using plasterboard is a successful solution and an alternative to isolation membranes.

If you just strip and replaster, the salts may well (will probably) show up again
Click to expand...
Thank you really interesting information!
 
As per @mrrusty 's post, I have worked in houses where the old soot/salts in the chimney stacks absorbed moisture throughout the year and pushed the moisture through the brick over the winter months.

One customer paid to have the whole exterior wall repointed, the flaunches redone and pot caps fitted because of the water stains on the chimney breast. The following easter I redecorated the room and applied SBR to the chimney breast. Later that year, the moisture stains came back. Turned out that it was hygroscopic salts in the soot.

The advice was to hack back the plaster and use sand and cement, but I can see how plasterboard held in place by expanding foam might suffice.
 
The following easter I redecorated the room and applied SBR to the chimney breast
Click to expand...

Yes, I've found SBR (i tried it as a slurry of SBR-cement) isn't a cure as well. My theory based on everything I've personally done is that any water based material + salts means that the salts get absorbed into the liquid water on application and during the drying process, as the water evaporates from the drying surface they get deposited on the surface to cause further problems by drawing water vapour out of the room ever after, and it doesn't make much difference what the material is - dab adhesive, plaster, sand and cement or whatever. I suspect if you can get a coating dry without further salt deposit, it can form a barrier, but it's the drying period that has the potential to just re-create the issue. What seems to me to be a 100% fix is isolation, however that is achieved, with a barrier that liquid water can't cross.
 
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