Wall discoloration on chimneybreast (Ed.)

[TMog]

Hi All,
Wondering if anyone had any idea as to what might be causing this on my chimney breast wall in my top floor bedrooms. We moved into our house 3 years ago and noticed the wall paint starting to peel/crack.

Wondering if this is a chimney flashing problem or possibly something to do with hygroscopic salts?

Any advice would be appreciated

 

[JohnD]

It looks like severe water damage.

Sometimes this is due to internal condensation where a flue is not ventilated top and bottom, but yours looks to me like a water leak, probably from the exposed chimney top. It might well be the flashing.

Go into the loft and look at the exposed chimney brickwork, and signs of water entry. Borrow a pair of binoculars or a drone and look at the chimneystack and roof.

The height of the water stain looks strange to me. If there is a ventilation hole, look inside to see if the cavity is full of builders rubble.

If there is not a hole, make one, because you need to ventilate it. Just above the skirting is a good place, and brick-sized is a good size. Look through the hole.

 

[TMog]

It looks like severe water damage.

Sometimes this is due to internal condensation where a flue is not ventilated top and bottom, but yours looks to me like a water leak, probably from the exposed chimney top. It might well be the flashing.

Go into the loft and look at the exposed chimney brickwork, and signs of water entry. Borrow a pair of binoculars or a drone and look at the chimneystack and roof.

The height of the water stain looks strange to me. If there is a ventilation hole, look inside to see if the cavity is full of builders rubble.

If there is not a hole, make one, because you need to ventilate it. Just above the skirting is a good place, and brick-sized is a good size. Look through the hole.

Thanks for the reply.

The loft has been converted into bedrooms so that is that is the top of the chimney.

Had a roofer out about a year ago who couldn't see anything wrong with the roof.

 

[JohnD]

Start with ventilation of both flues. There will have been a first floor and a ground floor fireplace, this is where the holes should be. And an opening at the top.

 

[mrrusty]

So the chimney doesn't go through the roof so it isn't water coming down. IMHO It's salts from the chimney. All the damp is most likely actually coming from the room air. Easiest way to isolate it is to overboard with 9mm plasterboard fixed with foam adhesive (not wet dabs). If you introduce any new wet trades to salt poisoned walls the salts will just migrate as the water evaporates on the surface.

Foam adhesive fixed PB isolates salts - worked well for me.

If the chimney does go through the roof, then yes, look at flashings etc because this will exacerbate - the chimney gets damp and then the damp evaporates in to the room drawings the salts through the structure. But, once salt poisoned, curing the leak won't cure the problem.

Everyone always talks about ventilating unused chimneys, but the science doesn't necessarily follow. You let nice warm humid air in at the bottom, it rises (as warm air does) up the chimney and any water vapour may then condense when it gets in to the cold loft space. Remember the dew point of ambient 20-22 degree 50-60% air is as high as 12-13 degrees! Arbitrarily allowing ventilation isn't a cure. It only works when the conditions allow that ventilated air to evaporate moisture, which means it must remain above the dew point throughout.