dark patches on attic chimney breast wall

A

Andrew Hoyle

New Member
Hello,


I have had an on going problem with darks marks that won't seem to go away. These marks are not wet, greasy or even colder than the rest of the wall, you can simply just see them. They were improving and going away but have recently appeared again (Not after rain, just generally cold weather). The never grow or change in size or appear any darker than they originally did but they have just reappeared in the same place. The area underneath and to the left of the beam is plasterboard, to the right is the chimney breast.


We have had various work completed.

:-This started off with having the wall taken back to brick with a salt neutralizer adding to the brick and left to dry overnight. A plaster coat applying to the area that was stripped back to brick and then a skim coat applying to the chimney wall and plasterboard area connected to the chimney wall.

:- We have had the chimney repointed, chimney cowl checked and confirmed there is no problems, lead flashings and underfelt completely redone around the chimney. This appeared to solve the problem but it has shown again in the exact same place. (I have had 5 separate roofers check the work who have all said how well the work has been completed and they can't see any problems.)


Does anyone have any idea what this could be? (a leak still, condensation, salts somehow still (Despite the salt neutralizer).


Any advice or even guesses would be appreciated.


Please see below pictures.

Original picture - then two weeks later - three weeks later - 4 weeks later and finally 4 and a half weeks later

dark patches on attic chimney breast wall
dark patches on attic chimney breast wall

dark patches on attic chimney breast wall
dark patches on attic chimney breast wall
dark patches on attic chimney breast wall



Thanks,

Andrew.
 
Are the fireplaces open or vented on the floors below?
 
No, fireplaces have been blocked off for at least 7 years (maybe quite a while longer than this but can't be sure). There is an electric fireplace mounted on the wall downstairs with the wires going into the wall. None of this has caused any problems over this time, only since we have replastered.
 
Andrew Hoyle said:
No, fireplaces have been blocked off for at least 7 years (maybe quite a while longer than this but can't be sure). There is an electric fireplace mounted on the wall downstairs with the wires going into the wall. None of this has caused any problems over this time, only since we have replastered.
Click to expand...

In which case, you need to put a vent into each fireplace (or where they were). They needn't be large or obtrusive, there's quite a range available.

If the flues are blocked at one or both ends the cold damp air will just sit in there as it can't circulate. With a vent fitted air can circulate from the house to atmosphere.
 
Andrew Hoyle said:
None of this has caused any problems over this time, only since we have replastered.
Click to expand...

You mean none of this has caused VISIBLE problems over this time. Those flues have been cold and damp since the end of the first winter they were blocked. What you have now is new gypsum based plaster where there was none before.
 
imago said:
You mean none of this has caused VISIBLE problems over this time. Those flues have been cold and damp since the end of the first winter they were blocked. What you have now is new gypsum based plaster where there was none before.
Click to expand...

Hello,

Thanks for the replies everyone.

The wall was plastered with gypsum plaster prior to having it hacked off and plastered again, would this still potentially cause the problem?

I forgot to say the house is solid walls built in approximately 1900, I would of used a lime based plaster or something similar but the wall had already been plastered with gypsum and appeared to show no problems.

I'm wanting to know if there is any way of telling what type of problem this is (e.g. a leak that needs fixing, salting, condensation or maybe something else). Then a way of resolving this (Like mentioned with vents which I am thinking might be the best way to go with this.)

Thanks again,
Andrew.
 
Andrew Hoyle said:
Hello,

Thanks for the replies everyone.

The wall was plastered with gypsum plaster prior to having it hacked off and plastered again, would this still potentially cause the problem?

I forgot to say the house is solid walls built in approximately 1900, I would of used a lime based plaster or something similar but the wall had already been plastered with gypsum and appeared to show no problems.

I'm wanting to know if there is any way of telling what type of problem this is (e.g. a leak that needs fixing, salting, condensation or maybe something else). Then a way of resolving this (Like mentioned with vents which I am thinking might be the best way to go with this.)

Thanks again,
Andrew.
Click to expand...
Hi,
As said above try fitting some vents.
The choice of materials should've been different, gypsum doesn't like any damp it acts like a sponge as soon as it comes in contact with any water, your property obviously haven't got cavity and it's solid wall construction, so should have gone with a bagged renovation plaster.
 
Andrew Hoyle said:
Hello,

Thanks for the replies everyone.

The wall was plastered with gypsum plaster prior to having it hacked off and plastered again, would this still potentially cause the problem?

I forgot to say the house is solid walls built in approximately 1900, I would of used a lime based plaster or something similar but the wall had already been plastered with gypsum and appeared to show no problems.

I'm wanting to know if there is any way of telling what type of problem this is (e.g. a leak that needs fixing, salting, condensation or maybe something else). Then a way of resolving this (Like mentioned with vents which I am thinking might be the best way to go with this.)

Thanks again,
Andrew.
Click to expand...

What was the old gypsum skim on top of though? As @zolco said gypsum plaster is hygroscopic and does not breathe well, so any moisture behind it will be drawn into it from the wall and doesn't transfer to the air as quickly as lime based plaster would.

The pattern you see in the damp area is where the moisture is transferring via the route of least resistance through the mortar joints. Given what you've said about it not being worse when it rains, and the work you've had done, you've pretty much eliminated a leak as the problem. That leaves cold moist air, and the best place to find that is in an unventilated cavity, which is what's been created by sealing up the chimney flues.

Two minutes spent on a Google search will give you the same information, and suggest the course of action already described.

I know you want a different answer, but you've asked for advice, and been given it. I don't want to sound harsh, but what's the point of asking for advice if you then ignore it?
 
Seems like he's looking for a magic cure. Fit the vents as you've been advised simple as that
 
I've did a job similar and the bloke had had everything done even his chimney rendered and all it needed was the chimney clearing out and a vent , the problem is the customer cant get his head around the simplest of solutions so goes around the houses ( no pun intended).
 
flynnyman said:
I've did a job similar and the bloke had had everything done even his chimney rendered and all it needed was the chimney clearing out and a vent , the problem is the customer cant get his head around the simplest of solutions so goes around the houses ( no pun intended).
Click to expand...
On a job once where an old terraced 2up2down, was being renovated ...
Biiiiigg damp patch on a first floor chimney breast.....no vents.....but as the guy was cutting the brickwork to put one in, he found nesting material.....loads....like two barrow loads! Jackdaws had been using it for years!
Cleaned out and vented, jackdaw thingy on the chimney top and "Roberts ya muvvers bruvver"...
 
Hello all,

I went ahead as suggested and got new vents in the chimney breast wall where the original fireplaces had been and also replaced the cowls from gas cowls to ones that allow a better airflow but still keep the rain out. That was at the start of April and it has improved. However there is one area that is staying persistent and not going away, any ideas or suggestions on what it might be?

dark patches on attic chimney breast wall


This part of the wall hasn't changed for quite a while now and I am unsure as to whether it is drying or there is still a problem. You can see where the original problem is from the pencil lines.

Any advice is appreciated.

Thanks,
 
It could still be drying depends how thick the wall is and how much moisture is in the wall or could be dry but stained stain blocker or Pva before painting it takes a while too cure
 
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