Damp - ground floor chimney breast & 1st floor ceiling.

[gpweston]

1916 mid-Terrace.

Four internal chimneys - rear ground floor in use, front ground floor & two first floors not in use. Chimney "balloons" fitted.

Front ground floor chimney has white furr inside, bubbled paint outside up to 60cm from floor. Moisture meter measures 20-30% in these areas.

1st floor ceiling has small yellow/brown damp patch which measures 20-30%

Chimney breast in loft is measuring 20%, cement seems crumbly in places, but no furr or mould.

However, roof and chimney were renewed approx 7 yrs ago.

Is all this probably caused by a problem with chimney pointing/flashing/leading/etc ?

 

[Joe Malone]

It's important to keep redundant chimneys well ventilated and chimney balloons stop the required through flow of air. Make sure the chimney is capped off, ensure airbricks are fitted, one at the top and one at the bottom then presuming there aren't any other sources of moisture the chimney should start to dry out.

 

[gpweston]

Thanks Joe

You think that damp in all three places could be coming from the top ?

We moved in 2 yrs ago. The chimney balloons were there already and the damp only seems to have appeared in the last 6 months or so.

We do have a de-humidifier, wound't you expect that to remove "normal" moisture ?

 

[Joe Malone]

The problem you've got is that hygroscopic salts are deposited in the flue as a by product of combustion. These salts will continue to draw moisture into the brickwork so it's essential to keep the chimney ventilated. If the chimneys not capped then you could also have a penetrating damp problem but the situation you describe is very common so theres a good chance that the measures I've described will help resolve the problem but you should be aware that six months drying out time might be required before you start and see results.

 

[Joe Malone]

Incidently don't forget, you've got a balloon installed so the dehumidifier isn't going to affect moisture conditions on the other side of the balloon.

 

[gpweston]

I assume balloons are normally fitted to capped chimneys just to stop heat going up them ?

 

[Joe Malone]

That's what they're for but they cause damp problems. You wouldn't lost that much heat with the airbricks installed. More often than not air balloons are a cheap option because these days it's expensive to get somone up on the roof to properly cap off the chimney.

 

[gpweston]

I understand capping can be done just by adding a cap to the top of the pots, so that the chimney is not permanently blocked off. Since they still allow air flow I assume air bricks will not be so necessary ?

 

[Joe Malone]

I'm assuming you mean a vented 'top hat' type cover on the existing pot? This isn't really capping the chimney off but providing you also had an airbrick installed at ground level then it should suffice. Normally you'd remove the pot and completely cap off with a concrete slab, then an airbrick would be installed just below the slab in the brickwork. You also need to install one at ground level to get the through flow of air. That's how i'd do it, wind noise can be a problem with top hat vents and I've seen them blocked with nesting material when chimneys are redundant.