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Internal chimney brick work will not dry out

I live on the top floor of a property. We spent a lot of money and time repairing our roof which we thought was causing an internall wall to be damp. The work done on the roof including repointing the stack, retiling where necessary, applying waterproof sealant on the brick work and capping and venting the pots.Then the building insurance came to repair the water damage from the inside. They took bits of the render/plaster/wall off and we can now see bricks from the chimney stack on the inside. We dried the internal walls with natural air for 4 weeks and it did not dry out. We then dried it for 7 days day and night with a dehumidifier and it dried nicely but the damp came back as soon as the dehumidifier was removed. What is baffling is that it has not rained or very little when the dehumidifier was removed but the internall bricks are still showing really high humidity readings. Everyone is baffled including roofers and surveyors. I did hours of research on this subject and came across hygroscopic salts as a potential culprit. I mentioned this to the insurance and their surveyor but they are dismissing it as they think the issue is still coming from the outside. If anyone has come across a similar issue in the past I would grately appreciate some information...

1 Answer from a MyBuilder Roofer

Best Answer

Hi, I've seen this a few times as a roofing surveyor for homeserve, many years ago. Unless the damp also travels around from the outside wall, or down from the ceiling, its highly unlikely to be a leak. The only causes can be, direct ingress from the pots (obviously not in your case), lack of ventilation inside the stack or, as you say, hygroscopic salt contamination. In many older type houses, you do get some "softer" bricks that may act as a magnet for damp air, especially if hygroscopic salt contamination is present. I'm surprised your insurance have dismissed this so readily, I've seen it many times (even on my own house) If the salts are the only logical explanation, then you will have to get the plaster covering the area off and re-done using waterproofer and a salt inhibitor. I'm not an expert in plastering so you may want to post a question to somebody that has experience in this. Regards Dean


Answered 6th Nov 2017

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