Damp patch on chimney breast advice

[Andoy]

Hi

For a number of years there has been a damp patch on the chimney breast in my attic. It only appears after prolonged rain and does not appear straightaway.

Over 12 months ago I had the lead work, pointing and flaunching redone. They also painted Thompsons water seal on the brickwork.

A month later the issue returned.
The pointing was done again and more water seal applied.

Over the next six months the problem slowly came back.

I suspected it was moisture being absorbed by the masonry so had some Stormdry painted on, this did not work.

I have recently sought advice from another roofer who stated it was coming through the brickwork and the solution would be spray some sort of block paving sealant onto the brickwork.

Has anyone had experience with similar issues and would a block paving sealant be suitable for a chimney?

 

[datarebal]

Check to see the cowls are sealed to the pots. Also there looks like there is a possible issue area at the top step to Saddle point .

 

[Andoy]

Check to see the cowls are sealed to the pots. Also there looks like there is a possible issue area at the top step to Saddle point .

Thanks. The lead work/pointing was rechecked recently and I was advised it was fine. I will have a look at the area you pointed out. The cowls have also been checked and are sealed.

 

[^woody^]

Pattern seems more like a flashing problem

 

[tell80]

All the old Flaunching should have been re-newed, and all new flaunching installed.
A new flaunching mix of sand, cement and chippings should be set 150mm min deep at pots or terminals & should smoothly slope to the four edges of the stack top - the stack is "Crowned".

Perhaps the original leak could have been due to any or all of the above thread suggestions - the long streak marks from what was maybe the original leaking can still be seen.

However, I suspect that the thick, black staining & various dark patches are Hygroscopic chemicals that have penetrated the c/breast brickwork? Hygroscopic chemicals obtain
moisture from condensation in sooty flues, & ambient air.
This would fit the pattern of damp showing intermittently.

Sooty flues - badly vented flues - moisture leaking down from the old flaunching - & moisture penetrating into the flues from the original, sodden, stack pointing - all or any of these factors could have created conditions for chemical activity in the flues.

Sweep the flues and make sure they are vented at fireplaces.
Check for any continuing leaking - go into the loft when its raining.
Obtain pics of the flaunching.

 

[Nige F]

All the old Flaunching should have been re-newed, and all new flaunching installed.
A new flaunching mix of sand, cement and chippings should be set 150mm min deep at pots or terminals & should smoothly slope to the four edges of the stack top - the stack is "Crowned".

and you should be - King of sand+lime

 

[^woody^]

However, I suspect that the thick, black staining & various dark patches are Hygroscopic chemicals

Hygroscopic chemicals?

Black hygroscopic chemicals?

Mould growing on surface moisture more like.

The damp, and mould is even on the underside of a rafter

 

[Andoy]

Thank you for all your inputs and advice.

The flaunching was redone in 2020 as was the lead work and pointing.

The chimney is shared with mine being on the right side, the dark patch is from the wood burner which has not been used for a number of years. The chimney was cleaned just prior to this. The dark patches are historic and don’t alter.

There are damp patches on the rafters but no mould. The whitish discoloured areas are where the dampness has dried out.

 

[tell80]

Andoy,
Thank you for the further info.

Ignore the ignorant creepy crawlies who would send you up the garden path just for mischief.
They are life'ss sad losers & must be pitied.

The chemicals attracting damp on the loft chimney breast could have been coming through the brickwork for many years.

How many fireplaces do you have in your house?

 

[Andoy]

Andoy,
Thank you for the further info.

Ignore the ignorant creepy crawlies who would send you up the garden path just for mischief.
They are life'ss sad losers & must be pitied.

The chemicals attracting damp on the loft chimney breast could have been coming through the brickwork for many years.

How many fireplaces do you have in your house?

Thank you! It is just one fireplace. It has not been used for a few years. The vents are open on the wood burner which is attached to the chimney. The damp patches are more on the left side which belong to the adjoining property which has no issues.
The dampness only comes when it rains and moisture can be seen sweating out of the rendering during prolonged rain.

 

[Nige F]

They are life'ss sad losers & must be pitied.

?

 

[tell80]

Just one fireplace for the whole property - thats surprising.
So you only have the one chimney breast with a fireplace - no other blocked off, or redundant fireplaces or missing chimney breasts? A blocked off fireplace in a bedroom?

You have a wood burner in the fireplace, and talk about open vents on the burner - I dont understand. Perhaps you would post a pic of this?

Burners typically have SS flex flue liners, one end attached to the burner it then goes through a Register plate, and then up to connect the top of the liner to a stack terminal/cowl - is this how your burner liner is fixed?

Is the loft used as a bedroom or something?

 

[Andoy]

By vents on the wood burner I just mean the air mixer controls.

No flue was put in, the fitter stated it was not needed.

There would have been a fire place in the bedroom above at some point but it was boarded over long ago.

The attic is just used as storage space.

Thanks

 

[tell80]

- Its not clear that the burner mixer controls opening will be a satisfactory bottom vent for your flue - is there a register plate above the burner?

- Who is the "fitter" what was the fitter fitting?

- "the chimney was cleaned out" - do you mean the burner flue was swept? Who swept it? When?

- the "fireplace in the bed room" that "was boarded over long ago" - the flue from that fireplace is separate from the downstairs burner flue, & needs opening up, cleaning out and sweeping and then left with a bottom vent in position.

- Two terminals can be seen on the stack - one presumably for the burner flue, and the other for the bed room flue? The bedroom flue is redundant - is the burner flue also considered redundant?
I ask because redundant flues have specific terminals/cowls.