being driven potty by damp chimney wall

[segiffin]

hello. around 5 years ago, i bought my house; around 70 years old brick/tile in very exposed position. the roof is chalet style and the stairs to first floor follow the roof line.

couple of years ago, noticed damp on junction of ceiling to stairway and flank wall. about 2 feet across directly underneath single skin chimney carrying gas central heating flue from kitchen. builder worked on chimney - repointing etc. still wet so builder did more work and replaced flashings, checked surrounding tiles etc.

no better and now yellow staining to adjoining bathroom wall. builder investigated further and found inside of chimney stackvery wet (almost mush) and flue liner 'like collander'. He removed chimney stack to just below roof level, relined flue, filed around and added high 'flue pole' on roof with windcatcher flue cap. when relining, builder found flank wall had been lined with plastic at some time in past and plastered over. removed and replastered.

kitchen filled with condensation whenever any wind. ventilation didnt help nor higher flue pole and 'super' cap.. gas guy suggested 'vortex of pressure' and said central heating fumes/gases probably discharging into chimney for years. suggested new system on other wall.

just done this. central heating good. now, no outlet/chimney stack on roof and tiling seems fine. however, wall is getting ever wetter. seems to be two parallel strips of damp approx 2 feet apart running down from ceiling for about three/four feet with one particularly wet spot at bottom. parts showing 'off the scale' on damp meter. can't access from loft ( chimney two feet below loft level) but above that, roof feels dry.

running out of money and patience and fed up with builders shaking their heads. do i need to remove all the old chimney from inside the wall(presumably still contaminated with years of fumes)? can i coat or cover the wall surface with something? how is it getting even wetter when it's now unused?

any assistance SO gratefully received. i think this website might be the answer to my prayers (fingers crossed) Sue

 

[Geoffrey]

Presumably now that it's not in use it has been sealed. Is it ventilated?

 

[segiffin]

hi geoffrey,

not yet. central heating system taken out three weeks ago (not in use for a month before that) gas guy said to leave hole in kitchen open as long as poss to allow wall to dry out. but when it rained, it got worse. roof is now tiled over at top. crawled about in loft last night. no signs of damp above the old chimney area. shoved my arm down between the tiles and roof lining and again, no damp. (technical testing hey?)
Sue

 

[Lime]

It is not easy to define the problem without seeing it (but obviously it is difficult even when you can see it) so I'll have a guess.

The plastic lining of the flank wall is a tell-tale of past problems.
The problem was not new when you first noticed the damp.
The two vertical damp lines are probably the flue's outline within the wall.
You (hopefully) have removed the other possible sources of water entry from the roof so it has to be one of three things:-
(not an exhaustive list)
1. Water is coming in through the wall directly from the outside.
2. The brick or plaster is hygroscopic.
3. A water pipe is leaking somewhere.

I would have thought the last option is unlikely with so many builders having looked at the damp.

Perhaps the damp wall takes most of the prevailing weather and the pointing allows water into the brick.
Perhaps there is a "cold bridge" where the brick is saturated and condensation from the house accumulates on the wall and the salts in the brick/plaster retain the water.

Anyway, the chimney needs to be ventilated.

One of the problems of simple gas flue linings is that the brick chimney is effectively closed up.
Within this lining there is often a lot of condensatation that can find it's way into the chimney.
(You say it was full of holes)
The air surrounding the lining is sealed within the chimney and doesn't change and ventilate the brick flue.

One way to ventilate, if you are not using the chimney again, is to block up all inside openings and open two outside ventilation points in the chimney top and bottom of the outside wall.
These will have to repel the rain while allowing air to enter.


Since this has caused problems in the past (evidence ~ the plastic lining under plaster) I expect the outside wall has been treated with a silicone water repellant too. Unfortunately neither "solution" cures the problem, it just makes damp worse as they trap water in the brick.

 

[segiffin]

Thanks very much for that.

Couple of points; the affected wall is internal - it runs up between the stairs and the kitchen and contains the old chimney. Couple of days ago, a builder went up in the loft again and this time, by crawling down between attic flooring and 'chalet' slope of roof, has found some wet on a rafter. He's now wondering whether rain is getting in 'somewhere strange' and finding its way along/across/whatever to run down the rafter and en route, running into the now disused chimney. certainly, when it rains it gets worse. But the tiles and lining look sound.

So, mystery deepens. I note your ventilation suggestion - thanks. It looks as if, yet again, men will be crawling around on my roof, taking tiles off and adding more lining, but I'm going to ask them to take out as much of the old chimney as possible this time. I'm still concerned about the brick work remaining behind the wall though; I'd wondered about the brick being saturated/hydroscopic and collecting compensation from the house.

I'm really quite angry about the plastic lining; it might have been an attempt to solve the problem but i'm wondering whether it was deliberately hidden so wouldnt show up on survey.

Thanks again for taking the trouble to respond. I'll keep you posted. Good luck, Sue

 

[Lime]

Well, from what you say the roof has been leaking all the time!
It is not unusual for rain to get into the loft then travel down beams to somewhere completely different.
The chimney may have been blamed and dismantled when there was nothing really wrong with it except a faulty leaking gas boiler lining.