Hello, I bought a victorian terrace about 6 years ago which needed flashings replacing all over the roof and some pointing done. This was all done and then we started renovating the downstairs...6 years later we're now decorating the upstairs!! The walls looked and felt fine and after 6 years we assumed any damp would have dried out so we just sanded and painted with standard paint.
But the two external corners (right and left) in the main bedroom at the front of the house are after 12 month both showing mottling of the paint and greasy looking patches that have spread about 70cm across and down the walls on both sides. I tried damp seal paint on the mottling paint but no good. I've been reading all the posts and two things have stood out, solution 1 - sand off mottling then paint with an alkali resisting primer and then see if that stops it, or solution 2 - remove old plaster and mortar 50% down each wall and add some salt stabiliser and SBR slurry (?) then seal with Aquaprufe (?) then dot and dab plasterboard or plasterboard onto battens.
Is there anything else I could try? The mottling isn't as bad as the greasy looking staining to be honest so i'd prefer not to have to go the whole hog and hack off render / plaster unless 100% necessary.
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