I have a damp chimney breast that had become damp because of the jointing around the stack on the roof. That had been sorted out last year but the breast remained damp. I then had the chimney stack removed about 2 months ago so there is no chance of any water getting in now but the breast remains damp near the ceiling and part of the plaster board ceiling as well. i've checked in the loft and there is no other problems i.e. missing tiles etc.
The fire place was closed off some years ago and has got a vent at the bottom and the chimney is open just below the roof. My damp meter still registers damp and the wall has a slight tint of brown, and you can feel it is slightly damp to touch. can i apply some damp sealant to it so i can repaint it white or is it a case of waiting for a long time before the damp dries out sufficiently
Although this is no help to you, Martinp, I have exactly the same problem on two chimney breast walls. One chimney is open with an infrequently used fireplace, and the other is closed. The damp affects the top of the walls and an area of ceiling. I'm pretty sure that there's no leak in the chimney flashings. The plaster is very old. I'm ready to replaster, but don't know what's the best method to use.
dampness to chimney breasts could be caused by a number of factors. Water entry due to the lack of a cowl, condensation with the flue due to the lack of ventilation (especially if the chimney has been capped with no flue vent) and salts within the plaster brought from within the brick/stone due to passage of moisture. Even if the cause of dampness has been solved, when salt contamination exisits dampness can persist. This is due to the hygroscopic nature of salts. in other words, the salt with attract moisture out of the air creating stains, and thus causing dampness.
The solution is to fit a cowl, vent redundent flues, check flashings and stack pointing and replaster using a sulphate/salt resistent compound and renovation plaster such as limelite or drycoat. And this rule goes with any walls that have been affected by dampness. Salt is one of the major causes of misdiagnosis of dampness.
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