Wall with damp patch on it - advice reqplease-Richard C

GJUK · 23 Jan 2011

Hi all,

Does anyoen ahve any ideas of what might be causing this damp area please?

The wall is in the first floor master bedroom, and it is an external wall behind which is a chimney stack.

Initially i thought it might be some poor flashing ont he roof or perhaps mortar joint worn away inside the chimney stack. However we have not had much rain recently and the damp patch is getting bigger.

Could it be the warm air in the room hitting the extra cold wall (due to the chimney flu behind this) and condensing on the wall?

I had to admit it can be quite humid in there but nothing major and there is no sign of condensation else where.

I'm stuck

Any ideas please?

Thanks

Jon

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tim00 · 24 Jan 2011

Post a plan view diagram of the problem area.

GJUK · 24 Jan 2011

does this help?

Thanks

Jon

GJUK · 24 Jan 2011

The photo taken is of the area where the blue arrow is pointing in the plan.

Thanks

r896neo · 24 Jan 2011

It looks like a classic case of damp in the flue. Is the flue used? if not it should be capped at the top with a ventilated cowl and also ventilated at the bottom.

GJUK · 24 Jan 2011

r896neo said:
It looks like a classic case of damp in the flue. Is the flue used? if not it should be capped at the top with a ventilated cowl and also ventilated at the bottom.

Hello.

It is not used at present, I will be installing a wood burning in there soon however.

I have a builder coming soon to fit a 'UFO' top to the chimney, do you recon this will help solve the problem?

What you say ventilated at the bottom? I've boarded it up downstairs to stop the wind blowing through, should i remove this?

Thanks mate

Jon

alanthomaswatson · 24 Jan 2011

Jon

Agreed, it looks like damp in the flue although where this emanates from will be another question. I'd cap the chimney with one suitable for still having your stove in (check with the flue manufacturer). This will reduce overall moisture in the stack due to rainfall.

It's also definitely worth removing the low level boarding - chimneys use to rely on the cycle of heating up and cooling to remove moisture but when chimneys aren't used this doesn't happen.

Whilst the flue is being capped, ask the builder to have a look at the flaunching, lead dressings and pointing to the stack. It may well be that any one of these are the main issue.

If the draughts are a major problem in the meantime, keep the boarding but install at least a brick sized vent cowl to the board.

Once the works have been done, keep an eye on the damp patch. Saturated plaster often doesn't dry out properly, and even if the original problem is sorted, the area will be prone to more condensation so you may have to re-plaster at some point.

Alan.

JohnD · 24 Jan 2011

To me, it looks like it is coming from the chimney, but it is mostly at the top, so I would start by going into the loft on a rainy day and looking for leaks, especially round the flashing and flaunching.

If a chimney is permanently disused, it can be helpful to have it taken down to below roof level, and have the roof remade above it. Then the flue will ventilate into the loft, and the tiles and felt will not need as much future attention as an old chimney would.

It is of course absolutely essential that nothing goes up the chimney afterwards, including smoke, gas fire fumes, or steam.

r896neo · 24 Jan 2011

If you can deal with the stains until then (and assuming when you say soon you mean within a few months) it may be best to get the chimney capped with a ventilated cowl and put a vent at the bottom until you get your wood burner in.

When you get the woodburner installed they will have to remove the pot and redo the flaunching around it anyway (perhaps). Also they will be lining the flue and filling it with insulation and seal it all up well so this will reduce any condensation and help the whole lot dry out.

Then after its been in a month or two you can redecorate the affected area. Chimneys and all the old soot and salts in them can stain walls when they get damp and it can be hard to get rid of so doing it now you may end up doing it again in 6 months where as if you wait til after the woodburner is in it might dry up better and simply need painted over.

GJUK · 24 Jan 2011

Firstly thank you very much.

r896neo said:
If you can deal with the stains until then (and assuming when you say soon you mean within a few months) it may be best to get the chimney capped with a ventilated cowl and put a vent at the bottom until you get your wood burner in.

ventilated cowl as in this 'UFO' type chimney top I'm having installed?

When you get the woodburner installed they will have to remove the pot and redo the flaunching around it anyway (perhaps). Also they will be lining the flue and filling it with insulation and seal it all up well so this will reduce any condensation and help the whole lot dry out.

sounds expensive, I was going to install the woodburner myself and not line the flue. But you think this is required?

Then after its been in a month or two you can redecorate the affected area. Chimneys and all the old soot and salts in them can stain walls when they get damp and it can be hard to get rid of so doing it now you may end up doing it again in 6 months where as if you wait til after the woodburner is in it might dry up better and simply need painted over.

Thanks

r896neo · 24 Jan 2011

yes the ufo is probably a vented cowl of some sort. there are lots of different types.

As for lining the flue, this is not always needed but in the majority of older properties it is. What age is your house? Even if you don't plan on lining it you must at the very least get it cleaned and checked by a chimney sweep.

Also fitting a stove is notifiable work so if you want to do it yourself you need to inform building control. There are many threads on the subject if you have a quick search for woodburner and look through some of those.

tim00 · 25 Jan 2011

Lots of good advice already given.
Q1 is this a hip roof? If it is it wont be possible to see the stack from the loft.

Q2 if the staining is due to moist soot ( ie. sulpherisation) penetrating the c/stack brickwork then it will require the plaster hacking off and re-rendering with a lime, sand and cement mix.

Q3 first, have all the flues swept and, as has been said, check the flashings esp. the back gutter,slates/tiles, ventilation, flaunching and terminal, and pointing - any ladder work to be tied-in.

Q4 dont be doing a bit of a job and then re-doing it later, find out whats wrong then do the complete job.the last thing you want is people constantly clambering about your roof.

GJUK · 26 Jan 2011

Thanks for the advice.

I've got a chimney sweep attending today, first step i guess.

Thanks,

Jon

GJUK · 11 Apr 2011

Hello all,

I'd like to update you on this problem ad ask for some more of your advice.

A few weeks have passed now and I have had a flu liner installed, wood burning stove and replacement chimney pot/stainless steel twin wall with top.

This chap (highly recomended) checked the roof while he was up there and confirmed that he could see no problems that might cause the damp.

To recap, when it rained prior to this work happening, it used to drip water down in the living room, down the chimney.

Since he has dones this work there has been no obvious signs of water in the stove. He didnt insulate the chimney but he has 'vented' it. I've had the wood burner on now and its certainly drying things out but then the weather is also drying up and the tempreture's are increasing.

(end of the waffle)

The damp seems to have spread a little since I last posted on here, see the photos...

My next door neighbour has the same problem in his house and he has told me that he thinks its the facia's and their lack of ventilation.

Is this possible?

I've attatched some photos for you to give your opinions.

Many thanks,

Jon

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GJUK · 11 Apr 2011

May I also add please that I have been in the roof space (loft) when it has been chucking it down with rain, with a light and can see no signs of water running in or under the tiles. There is no damp in the roof and all the tiles around (or as close to as I can get) the area just above this room are bone dry.

Cheers

diynot

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Wall with damp patch on it - advice reqplease-Richard C

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