Damp proof treatment in chimney stack? Advice please

ToneControl

Our chimney stack is on the outside of the flat outer wall, and the roof slopes down to meet it at gutter level

So inside the bedroom below it, there is no chimney breast, and we keep getting water stains coming through into the wall and ceiling below where the chimney is

That inner wall effectively carries on up through the tiled roof and becomes the outside of the chimney, facing towards the roof tiles above the bedroom

Looking in the loft, the course of bricks are visibly water stained, clearly water has leaked down leaching salts and minerals over decades. The visible brick course either side (which do not carry on past the roof tiles) are clean and look recently laid (it was built around 1920). These are normal 1920 bricks, not the exterior shiny engineering kind

We had a roofer up there fixing this a few times, most recently with scaffolding. He's a good roofer, and he has fixed the tiles and flashing. The roof is heavy old tiles on top of a full wooden roof, not just rafters. There is no felt or tarpaulin-type lining under the slate tiles. I wondered if water was sometimes being blown up under the tiles and dripping down.

Anyway, it was fixed in Feb/March, repainted, and we've had a few stains reappearing over the last month

I put a long cardboard sheet under the roof in the loft, and there is no sign of water dripping down from the slates

The only causes I can think of are: leaking at the flashing - but as I say - recently fixed by very good roofer, or water seeping down through the bricks. The roofer checked the pointing, and they are Accrington-type engineering bricks outside, so in very good condition. The chimney is tall and wide, and is capped.

I'm thinking I should have DPC injections into the stained bricks in the loft 

Does anyone have any experience / advice?

Kittyfrisk

Seeing your post reminds me of a situation I came across years ago with similar symptoms.
Turned out to be a condensation issue due to the chimney stack being capped off, thus leaving nowhere for moisture to ventilate.
This site covers it & it saves me typing 
https://www.londondampcompany.co.uk/chimney-damp-the-common-damp-problem-youve-never-heard-of/

more

Assuming the problem is fixed , the dampness in the bricks and  plaster will , in some cases ,  take a long time to dry out .    Plaster and bricks that have been damp for a long time will contain salts that will act like a wick and allow moisture to travel through the plaster and bricks easily. You can't remove the salts , but you  can  re plaster the effected  part of the wall . I would render the wall with cement that has has a water proofer added first and then plaster over it . You could  glue  plaster board on 
wall . You can get plaster board that is made for damp conditions . If this all sound a bit too much, you can paint a barrier on the wall . It actuly works better than it sounds , but it is not a  permanent fix 

ToneControl

more said:

Assuming the problem is fixed , the dampness in the bricks and  plaster will , in some cases ,  take a long time to dry out .    Plaster and bricks that have been damp for a long time will contain salts that will act like a wick and allow moisture to travel through the plaster and bricks easily. You can't remove the salts , but you  can  re plaster the effected  part of the wall . I would render the wall with cement that has has a water proofer added first and then plaster over it . You could  glue  plaster board on 
wall . You can get plaster board that is made for damp conditions . If this all sound a bit too much, you can paint a barrier on the wall . It actuly works better than it sounds , but it is not a  permanent fix 

we used damp seal already, it worked well on the 2 other rooms affected, but this chimney seems leaky still: no problems since March until this last month, so the Damp Seal is OK if no more water enters the bricks it seems

ToneControl

Kittyfrisk said:

Seeing your post reminds me of a situation I came across years ago with similar symptoms.
Turned out to be a condensation issue due to the chimney stack being capped off, thus leaving nowhere for moisture to ventilate.
This site covers it & it saves me typing 
https://www.londondampcompany.co.uk/chimney-damp-the-common-damp-problem-youve-never-heard-of/

well I plan to get a DPC firm in, so they can tell me if it's that

we had the stack repointed fully about 5 years ago, and it is capped, and there is a vent in that room, so not sure it's a ventilation issue

exocet

Does your chimney have a DPC / tray installed?

Dominic

Bricks actually take a very long time to completely dry and will have leached an effervessance    of salts into the plaster but it most probably a condensation issue irrespective of the stack being capped and vented because it forms what is known as a cold-bridge to the exterior.
Capped at top and a single vent in a breast actually does very little as you need good cross flow of air ;capping at top should also have some ventilation in it for airflow.
How many flues in the stack ? 

steveledzep

ToneControl said:

more said:

Assuming the problem is fixed , the dampness in the bricks and  plaster will , in some cases ,  take a long time to dry out .    Plaster and bricks that have been damp for a long time will contain salts that will act like a wick and allow moisture to travel through the plaster and bricks easily. You can't remove the salts , but you  can  re plaster the effected  part of the wall . I would render the wall with cement that has has a water proofer added first and then plaster over it . You could  glue  plaster board on 
wall . You can get plaster board that is made for damp conditions . If this all sound a bit too much, you can paint a barrier on the wall . It actuly works better than it sounds , but it is not a  permanent fix 

we used damp seal already, it worked well on the 2 other rooms affected, but this chimney seems leaky still: no problems since March until this last month, so the Damp Seal is OK if no more water enters the bricks it seems

This suggests to me that it is a condensation problem.  Cooler weather has returned.

more

I live  in a   nineteen thirties house with the  chimneys on the outside , as you describe.  Most of my   neighbours have taken the stack down to below the roof line and retiled the gap . I still use my chimneys , but luckily the previous owner had the chimneys, above the roof line , rebuilt.  

ToneControl

exocet said:

Does your chimney have a DPC / tray installed?

not seen anything like that in the loft.
This house is 100 years old, there was no normal DPC on the ground floor, it has some amazing weird electrical DPC fitted now that uses platinum electrodes

https://www.platinumchemicals.co.uk/products/lectros-electro-osmosis-damp-proofing-kit

ToneControl

steveledzep said:

ToneControl said:

more said:

Assuming the problem is fixed , the dampness in the bricks and  plaster will , in some cases ,  take a long time to dry out .    Plaster and bricks that have been damp for a long time will contain salts that will act like a wick and allow moisture to travel through the plaster and bricks easily. You can't remove the salts , but you  can  re plaster the effected  part of the wall . I would render the wall with cement that has has a water proofer added first and then plaster over it . You could  glue  plaster board on 
wall . You can get plaster board that is made for damp conditions . If this all sound a bit too much, you can paint a barrier on the wall . It actuly works better than it sounds , but it is not a  permanent fix 

we used damp seal already, it worked well on the 2 other rooms affected, but this chimney seems leaky still: no problems since March until this last month, so the Damp Seal is OK if no more water enters the bricks it seems

This suggests to me that it is a condensation problem.  Cooler weather has returned.

not sure, it seems to do it after rain

ToneControl

Dominic said:

Bricks actually take a very long time to completely dry and will have leached an effervessance    of salts into the plaster but it most probably a condensation issue irrespective of the stack being capped and vented because it forms what is known as a cold-bridge to the exterior.
Capped at top and a single vent in a breast actually does very little as you need good cross flow of air ;capping at top should also have some ventilation in it for airflow.
How many flues in the stack ? 

2 flues

Do you mean condensation from the air in the room onto the cooler plaster and brickwork?

boogieman

My stepson had a similar issue, he ended up deciding to have the stack completely removed and replaced with tiles. Unfortunately this made no difference at all, as the rain was actually getting in it at a gap in the flashing at the top edge of the roof and tracking down between the tiles and the underfelt. It then settled at the lowest point, which happened to be the stump of the stack, and made the ceiling damp. 

ToneControl

more said:

I live  in a   nineteen thirties house with the  chimneys on the outside , as you describe.  Most of my   neighbours have taken the stack down to below the roof line and retiled the gap . I still use my chimneys , but luckily the previous owner had the chimneys, above the roof line , rebuilt.  

The roofer recommended taking down the chimney stack as a long term fix
Trouble is the council removed permitted development rights for our house, I'm going to try to get them back

Mind you it's a massive chimney stack, and there are 2 others, one of which is twice the size

ToneControl

boogieman said:

My stepson had a similar issue, he ended up deciding to have the stack completely removed and replaced with tiles. Unfortunately this made no difference at all, as the rain was actually getting in it at a gap in the flashing at the top edge of the roof and tracking down between the tiles and the underfelt. It then settled at the lowest point, which happened to be the stump of the stack, and made the ceiling damp. 

I suspected that, but AFAIK there is no underfelt, so assume it would drip in higher up the roof
We had proper leaks last year on one stack, there was clear water running down the wall, and the roofer fixed the leaks as far as we know, so I'm hoping we have eliminated the leaky roof possibility

ToneControl

It's a hipped roof btw

NPP

ToneControl said:

It's a hipped roof btw

similar here, hipped roof with chimneys on the two outer edges, so rain water running towards them. Previous owners had one of them taken down and I had to get the other one removed because there was no way of getting on top of the leaks otherwise. No more damp patches since it's gone (that was a couple of years ago). 

Kittyfrisk

ToneControl said:

exocet said:

Does your chimney have a DPC / tray installed?

not seen anything like that in the loft.
This house is 100 years old, there was no normal DPC on the ground floor, it has some amazing weird electrical DPC fitted now that uses platinum electrodes

https://www.platinumchemicals.co.uk/products/lectros-electro-osmosis-damp-proofing-kit

Worth a read maybe?
  https://www.heritage-house.org/damp-and-condensation/all-about-the-pca/the-damp-con-collection/electro-osmosis-damp-proofing-systems-an-expensive-fraud.html

http://dampbuster.co.uk/electro_osmosis.shtml
YMMV...

ToneControl

Kittyfrisk said:

ToneControl said:

exocet said:

Does your chimney have a DPC / tray installed?

not seen anything like that in the loft.
This house is 100 years old, there was no normal DPC on the ground floor, it has some amazing weird electrical DPC fitted now that uses platinum electrodes

https://www.platinumchemicals.co.uk/products/lectros-electro-osmosis-damp-proofing-kit

Worth a read maybe?
  https://www.heritage-house.org/damp-and-condensation/all-about-the-pca/the-damp-con-collection/electro-osmosis-damp-proofing-systems-an-expensive-fraud.html

http://dampbuster.co.uk/electro_osmosis.shtml
YMMV...

interesting stuff
We have no damp anywhere in the ground floor AFAIK, been here 8 years, and done lots of work so would have seen it

The house was renovated by a building company who used it as an office in the 80s, I assume they fitted this system

Kittyfrisk

Also if you do a search on "does rising damp exist" then you'll find a world of highly informed professional contradictions.
Who knew that everything you once thought you knew, could be so confusing?
Still, every day's a schoolday... once the headaches cease.

hywelg

Done a bit of chimney  work myself, got 4 stacks on my house. There's two ways for you to get damp in the room below. Rainwater or condensation. If the damp is visible on a ceiling it's extremely unlikely to be be condensation. Open flues in old houses absorbed a lot of flue gas residues over the years and these absorb moisture and the bricks will never dry out your have to replaster with cement render then skim or you can use Limelite.  But these gases never affect a ceiling only bricks in the flue. 

Rainwater can get in in a number of ways. Soakers and flashings have a lifespan of about 80 years. Replacing one and not the other is foolish. Code 5 lead minimum for these. Some roofers/builders use Flashband as a bodge. Won't last. 

Flaunching around the pots or cap can crack with age and let rainwater in. Driving rain can get into poor mortar joints . Solution is to redo the flaunching completely, not just fill the cracks. 

When we did my son's roof last year we took the stack down to below roof level , might be the best solution if you're not using the flues and you think it might be rain getting in.