Top of bedroom chimney breast plaster is slightly damp

[swebb99]

Hi a couple of years ago I noticed that there was a bit of bubbling under the wallpaper and in a bit of the lath and plaster in ceiling just above on the top of the chimney breast in my front bedroom. At the time this was almost certainly from some leaking above in the chimney stack and the flashing. Since then I've had the roof done and also the chimney has been repaired and the flashing re-done, its also been re-checked since.

After the roof was done I patched the damaged plaster by removing it and re-plastering the area as seen in the pics (yes I'm no plasterer ). For a fair while its been fine but in the last 6 months or so I've noticed the plaster was darkening slightly and in area's has gone a little soft. I've used a moisture sensor on the plaster and it is reading about 12-19% where as the lower part of the breast is reading 2-7%.

I've gone in to the loft and everything above seems dry. I also had the chimney and flashing re-checked a while back and it was confirmed it all looked in good order. There is one pot on the top with a cap that and a gas fire in the ground floor.

So I'm at a bit of a loss, next door have a similar problem and somebody who checked it said it was something to do with the soot in the breast from years ago allowing moisture to enter more easily.

I should also mention I am working in this room and the radiator has been off the wall for probably 7-8 months or so.

Can I re-patch using a different mix or some kind of base layer to stop the ingress. Or maybe as the breast is between two fitted cupboards I could dry line on to battens ?

 

[blup]

Does the flue with the pot serve the fireplace in question? Capping it may have reduced the ventilation, combined with the fireplace maybe being blocked up and unventilated? These conditions can draw the damp through the breast from the chemicals deposited inside the flue after many years accumulation.

Blup

 

[swebb99]

Sorry when I said capped I probably used the wrong terminology. It's got a pot but there is a cover held on with wire which is 3 or 4 inches above the pot.

The chemicals you mention drawing the damp through the breast is what next door was told about his so it could well be that. I think he was told the plaster could be removed, the bricks underneath sealed and new plaster added on top.

I should mention the house is 1930's , solid brick.

 

[Loofah]

Where's the vent?

 

[swebb99]

There doesn't appear to be a vent. I previous owner probably a long time back must have removed the fireplace in the bedroom and sealed it up and removed the second pot from the chimney.

I'd assumed this meant the whole flue to the original bedroom fireplace would have been sealed off so no air would be flowing up or down it and this would be ok.

If condensation due to no vent was a problem wouldn't this cause more of the breast to be damp ?

if a vent is required where would it need to go, obviously I'm not keen on a cold flow of air blowing in to the bedroom.

Thanks.

 

[Loofah]

Damp is a curious thing. The unused flue should be vented for airflow throughout, so top and bottom. I'd be thinking a covered top and a vent where the fireplace was. If that wall is external then the vent can go on the outside wall

 

[swebb99]

Ah ok, well the breast has a flue for upstairs and downstairs so I would have to figure out from outside the path of the flue to the bedroom and break in to the bricks there, ideally behind the upstairs fireplace.