Damp proof treatment in chimney stack? Advice please

ToneControl

hywelg said:

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. 

it's definitely rain
the damp patches got much worse recently
And a massive wet patch appeared in one room this week, smack bang above the old fireplace location
I suppose that patch must be coming down from the pot at the top of the stack, or the flaunching, there is one crack in that but it's a stain bigger than 1 foot square, 10 or 12 feet below

In both rooms some gets into the whole wall across the width of the stack, and a bit into the ceiling
I've put cardboard above the ceiling, and nothing is dripping onto the ceiling

Our roofer has said he doesn't know what more to do, so I need to find a chimney expert around Cheshire
Any tips for finding someone with more than generic roofing skills?

I'd like to take them down, but currently I'd need planning permission (long story)

ToneControl

ToneControl said:

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

it only does it after rain, it's been massively worse this last week

ToneControl

ToneControl said:

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?

the other roofer/chimney guy who had a look at it says it's definitely not a condensation problem

ToneControl

Paging:    @hywelg @Dominic @exocet ;

any advice gratefully received

 OK

The guys I've had in say the stacks are leaking from the top, I can see a big crack in the flaunching on one of them
We have had scaffolding erected for the stacks, and need to decide how to fix

• Our favourite roofer A, known a long time says take off chimney pots, cover holes with slates, then put new flaunching over the top of the stack, using granite aggregate to strengthen the flaunching and make it last longer, fit airbricks to side of stack
• Expensive roofer B said fit paving slabs + airbricks

Roofer A will do it with paving slabs, it sounds more permanent to me. I don't want to pay £2k every few years for scaffolding to keep redoing it

Any recommendations please?
Roofer A is coming tomorrow to measure up for materials to buy
As it stands I'm planning to use slabs

hywelg

Neither, in order to maintain ventilation in the flue you need to simply renew the flaunching , not just patch it up, and fit cowls to the pots. 

Then put an airbrick in the flue as low as it can possibly go on the outside wall if that's possible,alternately a small vent on the inside wall. 

And there is a good argument to use lime mortar with a coarse sharp sand mix rather than hard aggregate and cement which will crack. 

Alternately take the stack down to the roofline and slate/tile over it. 

ToneControl

hywelg said:

Neither, in order to maintain ventilation in the flue you need to simply renew the flaunching , not just patch it up, and fit cowls to the pots. 

Then put an airbrick in the flue as low as it can possibly go on the outside wall if that's possible,alternately a small vent on the inside wall. 

And there is a good argument to use lime mortar with a coarse sharp sand mix rather than hard aggregate and cement which will crack. 

Alternately take the stack down to the roofline and slate/tile over it. 

all the pots have cowls already

None are in use, and we sometimes hear rain dropping down the chimney on windy days

hywelg

ToneControl said:

hywelg said:

Neither, in order to maintain ventilation in the flue you need to simply renew the flaunching , not just patch it up, and fit cowls to the pots. 

Then put an airbrick in the flue as low as it can possibly go on the outside wall if that's possible,alternately a small vent on the inside wall. 

And there is a good argument to use lime mortar with a coarse sharp sand mix rather than hard aggregate and cement which will crack. 

Alternately take the stack down to the roofline and slate/tile over it. 

all the pots have cowls already

None are in use, and we sometimes hear rain dropping down the chimney on windy days

The rain won't be getting round the cowls, it will be the cracked flaunching. 

All of my chimneys (I have 8 flues on 4 stacks) are either fully open or have half round tile cowls and I get no rain down them at all. 

ToneControl

hywelg said:

ToneControl said:

hywelg said:

Neither, in order to maintain ventilation in the flue you need to simply renew the flaunching , not just patch it up, and fit cowls to the pots. 

Then put an airbrick in the flue as low as it can possibly go on the outside wall if that's possible,alternately a small vent on the inside wall. 

And there is a good argument to use lime mortar with a coarse sharp sand mix rather than hard aggregate and cement which will crack. 

Alternately take the stack down to the roofline and slate/tile over it. 

all the pots have cowls already

None are in use, and we sometimes hear rain dropping down the chimney on windy days

The rain won't be getting round the cowls, it will be the cracked flaunching. 

All of my chimneys (I have 8 flues on 4 stacks) are either fully open or have half round tile cowls and I get no rain down them at all. 

I agree, the flaunching is the problem

We have 3 stacks, the left and right one have 2 flues each, the rear one has 5

this one isn't really leaking these days:

although when we had that storm recently, you could hear water dropping down the shaft (only audible in the night, because the flue is right behind our headboard), I assume this is just wind blowing some rain into the pots through the air vents?
It caused a few small stain spots on the wall, directly in line with the flue


this second stack has leaked loads, you can see why -there are big cracks in the flaunching :

The bedroom below this gets lots of water when there is a big storm, across the whole width of the chimney stack, it takes a few days for it to appear in the room


and then the big stack has been leaking a lot too:

this has deteriorated a lot
my study/recording room gets loads of spooky wind noise from one of these, as well as bloody wood pigeon sound effects, I assume it's the one on the left


So we can now repair them.
NB: No flues are used in the house

I think the Options are:

1. simply repair the flaunching, how long would it last? I should consider it as an option I think
2. cap off the stacks with toughened flaunching and seal flues with slate underneath that
3. cap off stacks with paving slabs

hywelg

Your lucky you only get the wood pigeon audio. We got the wood pigeon. Thankfully the fire wasn't lit!

I wouldn't try repairing the flaunching, replace it. 

ToneControl

hywelg said:

Your lucky you only get the wood pigeon audio. We got the wood pigeon. Thankfully the fire wasn't lit!

I wouldn't try repairing the flaunching, replace it. 

oh yes, definitely, but why not remove the pots and cap the flues too?
and how long does it last, and does granite aggregate make it last longer?

Kittyfrisk

hywelg said:

Your lucky you only get the wood pigeon audio. We got the wood pigeon. Thankfully the fire wasn't lit!

I wouldn't try repairing the flaunching, replace it. 

^ This, although mine was an irate jackdaw... twice.

exocet

If the stack is no longer required, best bet is to remove to below roof level and make good the "hole".

The next best option is to take down stack (assuming that lime mortar was originally used), insert lead tray and then rebuild stack / new flaunching etc. Obviously not a cheap option plus finding skilled bricklayers is not exactly easy nowadays.

As a minimum, completely remove and replace flaunching. Also replace any lead flashing at base of stack where it meets the roof.

In my old house, I had a chimney stack at rear of house (Victorian terrace) that looked similar to yours - capped off chimney pots / old flue from a gas boiler that was no longer used. The wall in the room that it went through was always damp / shiny after any rainfall. A combination of new flaunching, new flashing plus introducing  ventilation into the stack from the bedroom below cured the problem. I would have preferred to have removed the stack completely but as it was shared, the neighbours didn't want to entertain sharing the cost of the work.

imalrightjack

I haven't read the post in full but I'm absolutely convinced that most 'damp proofing' is an absolute scam.  Ventilation and air circulation, coupled with prevention of ingress of water will fettle any issues.  I bought a house two years back with damp at the gable end with a sealed up chimney.  Since sorting out a crack in the chimney and ventilating it, no problems.  I had many issues with a previous house and paid a fortune (I mean thousands) to a 'professional' damp proofing company - all work that had to be ripped out and started again, with their stupid membranes and bollocks.

ToneControl

imalrightjack said:

I haven't read the post in full but I'm absolutely convinced that most 'damp proofing' is an absolute scam.  Ventilation and air circulation, coupled with prevention of ingress of water will fettle any issues.  I bought a house two years back with damp at the gable end with a sealed up chimney.  Since sorting out a crack in the chimney and ventilating it, no problems.  I had many issues with a previous house and paid a fortune (I mean thousands) to a 'professional' damp proofing company - all work that had to be ripped out and started again, with their stupid membranes and bollocks.

there are a load of cowboys out there for damp work, quite true

one of these rooms, however, has water streams running down the wall like tears after it rains, ventilating the chimney (it is already) doesn't fix that

ToneControl

exocet said:

If the stack is no longer required, best bet is to remove to below roof level and make good the "hole".

The next best option is to take down stack (assuming that lime mortar was originally used), insert lead tray and then rebuild stack / new flaunching etc. Obviously not a cheap option plus finding skilled bricklayers is not exactly easy nowadays.

As a minimum, completely remove and replace flaunching. Also replace any lead flashing at base of stack where it meets the roof.

In my old house, I had a chimney stack at rear of house (Victorian terrace) that looked similar to yours - capped off chimney pots / old flue from a gas boiler that was no longer used. The wall in the room that it went through was always damp / shiny after any rainfall. A combination of new flaunching, new flashing plus introducing  ventilation into the stack from the bedroom below cured the problem. I would have preferred to have removed the stack completely but as it was shared, the neighbours didn't want to entertain sharing the cost of the work.

Already did the roof and flashing
These chimneys were too high to do at the time, needed scaffolding

I've talked to the roofer, decided to remove pots & existing flaunching, cover flues with slate, add airbricks, and cover with reinforced flaunching (with grano in it)