Hi All Can I ask some advice? I'm trying to paint over a plaster wall that has been damp in the past. The cause of the damp was fixed a couple of months ago but the paint just forms blisters of dry white powder and leaves the wall looking like the surface of the moon. How can I stop this? Any tips? Sam
What was the cause of the damp? If it was coming through the plaster from behind, it tends to carry soluble salts with it, which then concentrate and crystalise out as a white powder on the wall. This might well interfere with the paint. You could try washing with copious water and allowing to dry, but usually the area is replastered before redecorating.
Otherwise, what's the state of the wall you are painting onto, and what paint are you using?
Try washing the plaster with dilute brick acid (or white vinegar) - this will neutralise the alkali residue that leeches out of damp masonry. Then rinse well and make sure it's dry before repainting.
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