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Damp Proofing Question
Dark patches on chimney breast wall
Hi I just noticed I have 4 small patches on the side of 1 of the chimney breast wall, it's a fire place that has been removed and made bigger on the sides! I've felt the patches and it's not wet just dark patches! Could u help me?
We see this a lot. It normally occurs when plasterboard is "dotted/dabbed" on to the existing wall with adhesive. If there is any moisture getting in, the adhesive tends to absorb it which on its own has a darkening effect but if there is soot/dust in the area this can amplify it. If you get a leak onto plasterboard, particularly in the upstairs rooms the stains can be pretty much impossible to eradicate. The dust & moisture from the loft penetrates the board and no matter how much you re-paint it will keep coming back. You can buy off the shelf stain block products but they tend to be ineffective on all but light stains
Check that you haven't got any water penetration to the chimney, check that the adhesive wasn't placed directly onto a dirty surface (if it is plasterboard of course) and then the only remedies are to replace the board (best case) or install a membrane behind the board and then fix the board to the brickwork with plastic pegs and re-skim. Give the stain block a try if you are sure there is no water ingress and re-paint, it might do the trick and is the cheapest option.
Hope this helps
Answered 24th Sep 2013