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Damp Proofing Question
What to cover a damp exposed brick chimney with?
We've just bought a maisonette in a Victorian, 5 storey house. When we started decorating we uncovered an horrific brown damp stain (still damp) 0n the chimney breast in the top bedroom (loft conversion). The damp originates from where the breast meets the ceiling and peters out as it goes down- the bottom half of the chimney breast is completely dry. We discovered this brown stained plasterwork after detecting and then pulling down a partition wall that was built about 4 inches away from the chimney breast- all around. We found out that this had been a problem for a while and so finally in 2011 the freeholders spent £7000 on roof repairs to solve the problem and the source was located as flashing failure that and cracks in the chimney breast that were filled and sealed. We had a chimney sweep go up there to pop a rain cap on our chimney pot and he verified this work had been done but that it need a bit of re-flaunching. There was one brick missing in the breast after we took out a vent that was in the wrong place (in the flue from fire in room below which we have just had re-opened and swept ready to start using). Before it was bricked back up I felt inside and it felt drier inside than out.
1. Do you think it's likely that the chimney breast isn't still leaking but just never had a chance to dry out after the flashing failure because the owners were in a rush to plaster it and make it look good again for their tenants- so stain came back through so they drastically put up a wall as a quick fix? And because the bricks were soaked, but then covered in damp plaster and then trapped behind a partition wall with no ventilation (especially as all fireplaces were blocked off)- they just never have had a chance to dry out? The trapped warm, damp air just perpetuating the damp bricks? And now that we've stripped it and opened the fireplace insight of using it to burn logs- it will eventually dry out? If so, how long might this take?!
2) Also there was no heating in the flat for months after the tenants moved out and a new boiler as only just been installed- maybe this contributed to it not being able to dry out?
3)While we wait for it to dry out- what breathable stuff can we put on it to cover it up?! It is ugly patchwork with it's new brick and the dark patch and dusty- and this room was supposed to be our bay's bedroom!
Any advice, information would be gladly received!
The best thing to do would be to hack off the damaged plaster and further and re render using additives in the sand and cement to stop any hygroscopic salts coming through and making it waterproof then skimming any dampness inside should disperse and evaporate internally.
Answered 24th Feb 2013
It sounds like "sulphur" staining possibly caused by the leak. If the leak has been rectified you will find that this sulphur can and will absorb moisture from the atmosphere giving the appearance of "wetting".
Is the breast vented?
In a well-ventilated flue, warm air rises constantly, drying out the chimney. Moisture levels increase rapidly in a redundant flue if either the fireplace or the chimney is sealed. It is therefore essential to maintain ventilation to all flues, including redundant ones in particular, top and bottom.
Are you hacking off to the base brickwork? if so have you considered using lime based render rather than a cement based product which is none permeable. Being a victorian property I would imagine this is true to the original.
Answered 28th Feb 2013
The simplest solution is to overboard the chimney breast with insulation board (polystyrene backed plasterboard), moisture cannot pass through from the brickwork and it also insulates. The chimney breast should dry out internally once in use.
Answered 10th Jul 2013