Damp Proofing

Damp patches when it rains on chimney breast

Anonymous user 28/02/2024 - 3.31 PM

Wondered if anyone had any advice/tips for trying to get to the bottom of mystery moisture patches appearing on the chimney breast and edge of the ceiling just above it. (Included pics on http://www.diydoctor.org.uk/forums/mystery-chimney-breast-and-ceiling-moisture-patches-t43890.html) When it rains, certain patches of plaster go dark and are cold/damp to the touch. Initially the suspicion was hygroscopic salts and two patches of plaster were taken out and replaced along with salt neutraliser and damp proof additive. However, we removed some coving and found that there was also a significant darkened patch on the ceiling. This patch has made me wonder if it was the salts, as it seems to follow the course of a wooden beam above, with random spots here and there. In the loft, there is a gap between the chimney bricks and the chipwood floor and I wondered if anything was dripping through so covered it over in cardboard. That was bone dry, but last time it rained the moisture was back. I stuck my hand down into the floor and there were a couple of very small wet spots in the insulating fabric. This could be mouse wee I guess and a co-incidence. But I'm a bit baffled what could be happening. The bricks all feel dry and no real signs of any water damage etc. Any ideas? things to explore? etc? Some notes • Wood-burner installed, thus chimney no longer blocked up with trapped moisture etc. • New cowl fitted on chimney and flue put in. • Flashing - assessment of the installers of the wood burner, that all ‘looked in good order’, but not replaced.