Damp patch top of fireplace. Only happens when heating is on

[WusQuito]

Hi,

The chimney stack in my lounge seems to have moisture appearing right at the top of the of it. It also happens occasionally in the kitchen at the same height.

The strange thing is is that it only happens when we turn the heating on. We can have a really heavy down pour for five/six hours straight with not one damp patch appearing. When the heating goes on the moisture seems to be sucked in. The exterior brickwork has all been painted white (although it was done long before we purchased the house, it was also done professionally).

I have read into common problems with Victorian houses and a common theme seems to be moisture being pulled in through the walls due to a lack of ventilation and too much heat. We keep many windows on half lock through the house and we also have the original wooden front door which is quite drafty so that keeps air moving through the house.

Both the lounge and the kitchen have chimneys, the kitchen chimney has been removed halfway down with kitchen units installed underneath with an inset gas hob. An extractor has been mounted into the chimney.

The lounge fireplace is currently bricked up with a square left for ventilation (although it was tiled over, which we have sinced removed). We're just in the process of taking the bricks out and reinstating a coal fire which will help with ventilation.

There is a bedroom above the lounge which has a boarded up fireplace, no signs of moisture on the chimney at all. No moisture problems upstairs at all on the chimneys.

Before I get the builders in I just want to see if anyone has experienced anything similar.

Untitled

• WusQuito
• 8 Oct 2012
• 1

 

[big-all]

are all flues in the house open bottom and top [in use or vented top and bottom]

 

[joe-90]

It's condensation inside the chimney from warm moist air in the house and (if there is no flue) combustion gases.

 

[WusQuito]

Thanks for the replies.

With regard to the flues, I expect the one in the kitchen is open and the one in the lounge. Because we're opening the fireplace I have been able to take a look up the lounge chimney and about 3-4 feet up the chimney it has lots of old sticks and vegetation which has been dropped down by birds over the years. I'll get that cleared.

The two upstairs chimney openings have both been sealed.

I'm going to get someone to check the chimney caps to see if any have been closed or obstructed restricting airflow.

The kitchen problem seems slightly different as the moisture is only appearing above a window and in the corner. I keep the window on half lock at the moment. Obviously my walls are not of cavity construction so I expect that there's possibly a weak spot somewhere on the outside allowing excess moisture to get through.

Anything else I should check?

 

[big-all]

does anything vent into breast [ gas boiler extractor fan] or pass through it like heating pipes

 

[WusQuito]

There are no pipes of any kind running into the chimney.

After reading a few more threads on here I think this may be caused by hydroscopic salts penetrating the plaster and I expect the same has happened in the kitchen. While I'm reinstating the fireplace I might aswell take off the old plaster and re-apply with a gypsum free mix. I can't do the plastering but I can remove the plaster to save myself some money. Shouldn't be more than a days work for the plaster either.