Help - repair chimney or remove ?

[Stuartyboyhere]

I have what appears to be damp staining on the wall of my upstairs bedroom. I have been told that the rendering on the chimney stack adjoining this wall is in a poor state. A roofing contractor has quoted me £400 to re-render the stack and replace the flashing.

I asked him about dropping the stack and tiling over for which he has quoted the same price of £400. I believe this would eliminate the problem forever.

Could anyone advise best way forward. Is stack removal an overkill ? What would I have to do about my gas flue ? What other hidden downsights are there ?

Stuart

 

[js.roofing]

Before you go ahead with replacing the flashings, double check with the roofer that your chimney has a lead tray fitted as your £400 will be a waste if its leaking due to no tray. Also check what flashings are being replaced most chimneys leak from the behind gutter due to a split somewhere or incorrectly dressed lead, so make sure this is included and not just the side flashings unless it is evident that its leaking from the side. Chimney removal isn't overkill, as you say it will eliminate the problem for good, you will probably need a corgi fitter to fit a new flue though, and lead slates to go with are available at any roofing merchant.

 

[Stuartyboyhere]

Following this message from 2007, I employed a local builder to remove both chimney breasts above our slate line in December 2011. The work involved new batting, felting, slates and gutters with twin walled flue pipes/flashing added to take care of my gas fires.

Six months has passed and I still feel we are getting shadows on the walls which feel slightly cold and damp. The dampness on one room is 'peppered' across most of the upper section of the wall. The builder has been back to examine his work and advises that the new flues look fine. He is at a loss to what is causing the problem but I asked if the dampness could be crossing the cavity via the cavity ties or being assisted by cavity wall insulation we had put in some 2 years ago.

Assuming the flues are watertight would a full re-render/pebbledashing of this gable end wall give me the barrier needed to sort out my problem ?

Any help appreciated

Stuart

 

[joe-90]

It's got fook all to do with your chimney. You have a condensation problem.
Warm air from the house is condensing in the chimney and the damp is coming through the breast. Why so-called tradesmen can't get that into their heads is a mystery.

Take a look at a few end terraces and you'll see a line of damp all the way from bottom to top following the chimney.

 

[Lower]

So how do you deal with this? Sounds similar to a problem i have.

 

[joe-90]

You either have to ventilate the chimney bottom and top or seal the chimney so moist air can't get up.

A damp block painted on the wall will do a temporary fix or hack the plaster off and re-render using an sbr slurry (waterproof) to stop the damp coming through.

 

[Stuartyboyhere]

Joe,

Thanks for your prompt reply and I'm extremely interested to hear your comments ! Just to clear up my thoughts - if I have open gas fires in each room which exhaust through a 5" twin wall flue pipe, does this not create adequate air circulation in each room through the remaining chimney stacks to dry out any condensation ?

Would be grateful for your thoughts on that scenario. Thanks

Stuart

 

[joe-90]

Do you mean a flue liner? Or do they vent straight up the chimney?
Either way, it's a condensation issue and is very common. Even a capped chimney suffers the same. Warm air rises up the chimney, cools, deposits its water droplets and drifts back down to be replaced by more, warm, moist air. It's a sort of heat engine at work.

 

[Stuartyboyhere]

Just a few add on queries with this ongoing problem ;

- had a single air brick put into each stack about 4 foot up from ground level approx 7 weeks ago. I've haven't noticed any 'drying out' of the bedroom wall stains/spots since having the air bricks were insterted. The question is do I need a second air brick at the top of each stack to give some circulation ?

- another contractor dropped by this week and he believes I have FLUE DAMPNESS with associated hygroscopic salts. He is proposing I consider replastering using a 'tanking membrane system' followed by full replastering of the bedroom wall in question. Is this the best sealing method to stop the spotting problem coming back through ? How would this compare to an SBR based plaster coat ?

All views appreciated

Stuart

 

[Alastairreid]

Read this.

http://www.buildingconservation.com/articles/services/chimney.htm