Damp chimney breast

[marlonhambo]

Hi all,

We've been struggling to diagnose a damp chimney breast since moving into an Edwardian semi 4 years ago and it is quite frustrating (and expensive).

We originally had a lead valley replaced, between the roof and parapet wall.
We've since had the parapet wall and chimney breast repointed. And most recently we've had the pots re-flaunched, as well as some air bricks install (as they are no longer working chimneys).

The pots were flaunched about 5 weeks ago. I have a pinless moisture meter and a dehumidifier. The dehumidifier has been running and probably taken 30 litres of water out. Up until 26 April the readings from the damp meter were down from 100 to around 80-90. The dehumidifier was running but was collecting less and less water.
On the 27th the damp patches became slightly more prominent and so I took fresh readings and annoyingly we were back up to 100. There probably was a bit of rain overnight on the 26/27th. But we also had some new radiators put in downstairs on the 27th and I cranked the heating for a few hours to test those (and because the floorboards were up it was cold anyway).

I put the dehumidifier back on and it's been running for 24hours and collected 3-4litres of water again. The surface readings are again back to around 80-90.

That's an awful lot of waffle but wanted to give some background and the fairly simple question is how long might we expect for this to dry out, brick, lime plaster and papered walls AND is it normal for damp to continue to rise to the internal surface.

Could the higher readings have been explained by the heating on and the damp being drawn to the surface or might it indicate the underlying issue has still not been resolved?

Thanks

 

[Emotionalrollercoaster]

Sorry, I don't know the answer but hoping I might find some answers of my own as people answer your query as I also have a damp chimney breast! Mine is damp just at the bottom by the skirting boards.

My property is a 1929 semi with an internal shared chimney that has been blocked up (no ventilation).

The bottom half of the wall is gypsum (presumably added when the dpc was done) and top half is lime.

I'm just wondering (and here is where my query might help yours!) if replastering the chimney breast with lime plaster might resolve the damp issues?

 

[88v8]

...how long might we expect for this to dry out, brick, lime plaster and papered walls AND is it normal for damp to continue to rise to the internal surface.

Could the higher readings have been explained by the heating on and the damp being drawn to the surface or might it indicate the underlying issue has still not been resolved?

Drying time roughly a month per inch of wall thickness.

Are the flues open top to bottom, ie fully ventilated? Whereabouts is it damp?

Sorry, I don't know the answer but hoping I might find some answers of my own as people answer your query as I also have a damp chimney breast! Mine is damp just at the bottom by the skirting boards.
I'm just wondering (and here is where my query might help yours!) if replastering the chimney breast with lime plaster might resolve the damp issues?

No.

Is the flue open at the top? If so, rain is coming in. If not it's internal condensation. The flue needs a through draught with a capped pot or airbrick at the top, and an airbrick at the bottom.
There... a nice simple solution...

 

[marlonhambo]

This is a photo from October 2021 with the most visible issue but it has calmed right down since.

2 of the flues are closed at the bottom (one removed completely)

Perhaps I should look at getting an air brick at the bottom of the stack?

The flaunching was cracked, when that was being replaced they noted that the chimney caps were loose and water appeared to be getting down there, so those have been siliconed in place.

My main question is would the water that is held in the brick and plaster from the last few years continue to rise to the internal surface, would that be normal behaviour? Or once the first inch is dry internally it would stay dry?

 

[Cubist]

My main question is would the water that is held in the brick and plaster from the last few years continue to rise to the internal surface, would that be normal behaviour? Or once the first inch is dry internally it would stay dry?

To the first question - Yes; the water in the stack would in effect be drawn toward the much warmer surfaces and air indoors.
To the second question - It depends; but if the internal surfaces remain dry thoughout a year then they probably will stay dry. In my opinion, the house needs to be exposed to the full annual weather cycle before you can be more than reasonably sure.

 

[marlonhambo]

Thanks Cubist.

With the internal damp readings going down over the last few weeks but then rising again I was concerned the underlying issue has not been resolved but it sounds like it COULD be the stored water working it's way out.

I'm hoping to use this room as a nursery in about 6 months, so would like to keep on top of any issue.

More patience required for now

 

[Emotionalrollercoaster]

Sorry, I don't know the answer but hoping I might find some answers of my own as people answer your query as I also have a damp chimney breast! Mine is damp just at the bottom by the skirting boards.

My property is a 1929 semi with an internal shared chimney that has been blocked up (no ventilation).

The bottom half of the wall is gypsum (presumably added when the dpc was done) and top half is lime.

I'm just wondering (and here is where my query might help yours!) if replastering the chimney breast with lime plaster might resolve the damp issues?

Awesome, thank you! I'm looking into the chimney ventilation and capping as we speak.

 

[88v8]

2 of the flues are closed at the bottom (one removed completely)

Perhaps I should look at getting an air brick at the bottom of the stack?

Yes, there needs to be a through-flow of air.
The lower down you put the vent the better, in or just above the skirting would be best.
Check however that you are actually venting into a hole, and not a space that has been filled up with debris.

Goodish job up top on the stack, the flaunching is a bit Mr Blobby and may collect moss. With vents top and bottom the small amount of water that leaks in around the caps will not be a problem.

 

[Stevers]

There looks to be a parapet wall each side of the chimney, and the water seems to be ponding there. It looks like there's been some recent work done, but it would be worth double checking that the gutter lining behind the parapet and the capping is as it should be. Such designs are reliant on sound original detailing and timely inspection and maintenance.

 

[CliffordPope]

The vents at the top of the stack look a bit close to the roof don't they? I'm picturing a deluge of rain sluicing down the roof and hitting the stack and splashing down the vents.

 

[marlonhambo]

Thanks for all your replies.

This photo was immediately after the work to re-flaunch and install the air bricks, so I think they washed it down after.

I have been running the dehumidifier constantly since this post, probably extracted another 15 litres of water and the readings are back down again.
I'm reasonably hopeful that the issue is now fixed and it's just a case of getting the existing water out of the stack and that I was premature in shutting down the dehumidifier.