Hi, my neigbour's chimney has started to show a damp patch coming
through our bedroom wall. Since weve just decorated with expensive
wallpaper were a bit annoyed by this. They have had a wood burner
installed in the last 6 months (no liner) and I'm concerned that this
may be the cause of the problem. Who would be the best specialist to
advise what the problem is so I can go armed with the facts as to
whether its the wood burner, or just damp from a leaky tile etc. How
much can I expect to pay for such a service?
There are two possible issues. Are the stains the result of the
recent change to a wood burner?
Are the stains the result of fossil fuels over the last century or so
- a common cause of hygroscopic salts (usually a light brown or yellow
For the former I suggest you look at building regs and see if the wood
burner has had a proper flue installed and, if so, it can be
If not then an expert in installing such wood burners and the effects
of not doing it properly is the person to call in
If it is fossil fuel burning then you need no expert. Just remove and
render the affected plaster or if that does not appeal "botch" it by
covering with a specialist stain plaster
Do check that there are no indications of water penetration from
quite possibly, I need to determine which therefore.
No flue installed (I asked at the time because I was concerned). Also
it seems like the capping hasnt been replaced - there seems to be only
a small gap between the slab and the chimney top for smoke to escape
(about 3 in I estimate). When I installed my burner, I changed the
slab to a chimney pot, hence my concern!
Will they be able to definitively tell me if its damp or tar? Can damp
also be caused by condensation of the combustion vapour the top of the
flue as I dont see the stain further down the wall, or downstairs?
It could be fossil fuel since thats what a house built in 1863 would
have used for years, although none of my other walls over chimney
breasts have such stains despite being used for fires/wood burners. We
had upstairs decorated recently, but I dont recall any stains on the
old (albeit thick woodchip) paper. Furthermore, our new, now stained,
paper is one of those embossed Laura Ashley types, and I can see the
stain/damp coming through it even though it is probably more resistant
than the lining paper used everywhere else (including over the other
Will do - are the damp meters any good for detecting such penetration?
If it is a wood burner and improperly vented it is probably a fire
hazard as well as a source of tar discolouration. If it is damp a
small gadget will tell you. If it is tar it will be yellow and stain
through all known wall coverings.
No paint made will stem it. Maybe some Visqueen under aluminium faced
plaster-board might. For a while.
You are wasting your time getting in an expert. An house surveyor will
charge hundreds and may exclude the terminology you'd need to win a
law suit. They have seen the light about public liability.
If you can convince your neighbour he is a fool, he might stop acting
foolishly but how likely is that? The tar will eventually spread
around the entire building. It is as insidious as mould.
Get a ladder and check the chimney tops. If they are open and you
don't have fires below them, you need to cover the vents and leave a
small air gap. And you need to cover the fireplace and vent that too.
Also check for damage to the sides of the chimney. Missing lead
flashings for instance. A lot of scrap metal crime is going on at the
moment. Maybe you have been a victim.
I'll try and get the gadget from screwfix to determine if damp or
stain from tar - but is it not possible that it would be damp and tar
- both from the fire due to improper venting (see my other reply re
condensation as their fire is not used that regularly as far as I can
Even if I convince him to stop using the fire, the next person may not
be so obliging, so I need to stop it now and before we redecorate
There is a ground floor and first floor flue feeding the chimney (both
on his side). The downstairs one is fitted with wood burner (no liner)
and the upper is sealed I believe (probably vented if my fireplaces
are anything to go by). Chimneytops no longer have pots on this stack,
and have a slab over both flue exists with what I consider to be a
small (3-4 inch) gap.
I've just got the recommended gadget and it is clearly damp coming
through the wall/chimney. 0-5% moisture on unaffected patches and
30-35% as soon as get to the "stain" part of the wall paper. Whether
there is tar/something else also coming through at the same time I
dont know. I've been into the loft to check for water ingress. Put my
hand on the chimney breast bricks directly above the stain in the
bedroom and cannot seem to find any obviuos indications of water
coming in. Besides which the stain is in a the shape of flue - i.e. it
snakes up at an angle rathen straight down - it also gets wider at the
top and narrower at the bottom - both of which I would suggest are
issues with the wood burner. On the other hand, if they dont use it
for a while, surely the stain will dry out?? That would confirm
whether it is the burner or not - or am I missing something?
Anyway any advice gratefully received as per usual!
1. damp meters measure resistance, not damp. Soot conducts too.
2. the solution was explained last month.
3. If you want a guarantee you'll need to employ a building firm
willing to give a written g'tee. for which you'll pay silly money.
What evidence have you that damp is coming THROUGH the chimney? In
what way does a reading on the surface with a resistance meter
indicate this rather than hygrosopicity which comes and goes WITHIN
THE PLASTER with the RH and which was presented to you as an
alternative explanation when I said
Are the stains the result of fossil fuels over the last century or
- a common cause of hygroscopic salts (usually a light brown or
I have been surveying such properties for well over 30 years and in
the vast majority of cases it is not external water penetraton from a
cover flashing or the like but hygroscopic salts contaminating the
PS btw the 'percentages' are not percentages of moisture content but
an indicator of relative resistance
Good advice from Weatherlawyer. It sounds as if you need a good local
builder to take a look at it but I can't tell you how to find one.
One thing. Have you had your chimney breast removed? if not then I
would expect the stains to be a lot worse on his side.
Thanks for replying. Chimney breast doesnt exist my side and never did
- were in a terrace and hes the end one so theres no back to back
arrangement on that side - it is back to back on my other wall
however, with no such issues.
Probably either hygroscopic salts or fumes leaking through cracks
in the chimney to meet the back of the paper. Either way, removing
the patch of plaster back to the brick and replastering it would do
Beware of damp 'experts', most are better avoided.
On 25 Feb, 15:21, firstname.lastname@example.org wrote:
True, that may work but I want to be certain it doesnt happen again
before I redecorate (even if he pays - I'm fed up of the DIY
disruption!). If its leaking fumes, then making him install a liner
seems the way to go - but can I make him do that legally, if he doesnt
want to play ball?
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