Damp on old chimney breast

[gregmcateer]

Some advice, folks, if you please.

Chimney completely removed below roof line and roof tiled across. All fine, we thought. A few years later, we're noticing damp patches appear.

I wondered about cold empty chimney space and thought about stuffing the space with eg rock wool. I have now read about 'hygroscopic salts'.!!

So should I strip off all plaster and seal then re plaster? The blue painted wall is the adjoining room behind the fire place

 

[Spectric]

Sounds like you have no airflow through that chimney and it has become an enclosed unvented space. You cannot try and seal or hide the issue as it needs fixing, all you will end up doing is moving the problem elsewhere because the damp needs to evaporate.

 

[rogxwhit]

Yes, it sounds like the remaining flue below the roof line is a cold, uninsulated space within the structure, and the damp is from condensation within and around it. If you can insulate within it, all to the good, but best if you can ventilate (to a roof-space?) above that insulation. Otherwise rockwool (et al) could end up a soggy mass ..

 

[Pedronicus]

What happened to the fireplace that the chimney used to serve?

 

[gregmcateer]

Hi


































































































































































Thank you for your speedy responses. I thought that might be the case but didn't want to make it worse, or spend time and




































































































,

 

[gregmcateer]

Sorry, I have no idea what happened to my reply. Thanks for advice.
Pedronicus, the fireplace is just empty, unused

 

[Pedronicus]

Sorry, I have no idea what happened to my reply. Thanks for advice.
Pedronicus, the fireplace is just empty, unused

Has the top of the fireplace opening been sealed up? If so then perhaps a small grille inserted to allow a flow of warm air to waft up the ex-chimney may help.

Also is the chimney internal or on an outside wall?

 

[gregmcateer]

A grille is a cunning plan, and cheap!
Many thanks folks.

 

[gregmcateer]

Has the top of the fireplace opening been sealed up? If so then perhaps a small grille inserted to allow a flow of warm air to waft up the ex-chimney may help.

Also is the chimney internal or on an outside wall?

The chimney is on a corner. Left of fireplace is outside wall and it backs onto an inside wall - where the damp is showing on the blue wall in picture 2

 

[Pedronicus]

Might be worth a pop up into the roof space during heavy rain with a big torch to make sure the tiles that were fitted over the hole left by the removal of the external section of the chimney aren't letting water through and running down inside the stack. Or maybe the external pointing on the existing outside wall side of the stack has failed and letting water through.

 

[gregmcateer]

Good thinking. However there is no roof space - the room wall is pitched down past the fireplace. I've kept a close eye for leaks and there are no signs of any water ingres at the top of the chimney breast so guessing it's condensation or hygroscopic salts drawing in moisture

 

[baldkev]

In terms of salts, sometimes a wipe over with vinegar can stop it reacting/ coming through. I think the term was efflorescence ? I'd conside a dehumidifier to help draw out some moisture first. The chimney could be filled with vermiculite? Although the grille is a good option for getting air through if not.
Lastly, its possible the moisture could be tracking in from the outside wall and into the interior from the sides of the chimney, so worth having a look at the exterior wall. Is it pointed stone? Or has the paintwork been left for a number of years?
Im no expert, but my understanding is that new paint forms a film, which after a few years will have deteriorated enough to allow algae etc to take hold and eventually water can get in

 

[gregmcateer]

Thanks Kev. Further investigation to follow...

 

[pe2dave]

A grille is a cunning plan, and cheap!
Many thanks folks.

And feed it warm air to dry it out perhaps?

 

[KeenToLearn]

Hi GregMcateer,

Sympathise; we had our chimneys removed to below the tile line about 2 years ago and tiled across, but were still getting damp/ condensation issues on both ground and first floor levels. Finally found problem- the chimney was originally removed to barely just below tiles, which was then a cold point for warmer air coming up chimney to condense upon. So removed further bricks to attic floor level, and capped with insulation on top of capping and air brick into roof space since which no issues crossed fingers. Your problem I guess is where to put an air brick to ensure ventilation? Either to outside or into attic room to ensure through flow? Or, perhaps as you have already removed chimney above, why not remove whole of chimney breast in attic room so air travelling up has no cold spot on which to condense?

 

[gregmcateer]

Thanks, KtL. We're probably going to take it right out - gain the space in the room.
Cheers all for the advice
Greg

 

[rogxwhit]

And feed it warm air to dry it out perhaps?

Except that the warmer the air, the more moisture it may contain, and thus the more moisture there will be to condense ...