Yellow stain on ceiling where chimney exits - I assume it's damp?

[volks]

See attached. Was hidden behind some coving, I initially thought it was yellow paint on the old wall, painted over with Matt and it came back the next day. I scraped some plaster off to the cement board and it looks dry.

Unfortunately I can't get to the roof to view where the chimney meets as it's blocked by the dormer. Might get the ladder out when the wind calms down.

For now, trying some zinniser stain block while I wait for the wind to die down, but would appreciate any advice people can give!

 

[JohnD]

Yes, yellow stain is common where damp in a chimney picks up soluble material from soot.

Is the chimney ventilated top and bottom of both flues?

Photos would help, of the stack and of the chimney in the loft which may show damp.

 

[volks]

Yes, yellow stain is common where damp in a chimney picks up soluble material from soot.

Is the chimney ventilated top and bottom of both flues?

Photos would help, of the stack and of the chimney in the loft which may show damp.

Chimney is ventilated at the top that I can see, the previous owners had a gas fire fitted and a metal flue liner fitted in the chimney stack. That's been blocked internally to stop heat loss and the gas fire removed.

The chimney isn't in the loft as the house had a dormer conversion, so the bedroom that I took the photos in is what used to be the loft. The flat ceiling above is where the dormer flat roof reaches the pitched roof outside.

I can't provide a photo of the side of the chimney that is damp from the outside as you can't see it from ground level due to the dormer

 

[JohnD]

You need ventilation of the bottom of the flue from each fireplace

 

[volks]

You need ventilation of the bottom of the flue from each fireplace

How are you meant to professionally seal an unused chimney to stop this problem? If I unblock it in the living room, all the heat from my central heating will surely escape up the chimney flue, wasting my money?

 

[volks]

Excuse the bad picture , it's the only one I had to hand. This is how the chimney is set up in the living room, I've blocked the metal pipe inside the chimney, not the entire brickwork itself.

 

[JohnD]

How are you meant to professionally seal an unused chimney to stop this problem? If I unblock it in the living room, all the heat from my central heating will surely escape up the chimney flue, wasting my money?

It will typically be an airbrick, or a grille, quite low down. It will not suck all the heat out of your room.