The wife and I live in a lower flat (built in 1900), not surprisingly the flat has had extensive damp proofing work over the years.
Recently a damp patch appeared in one side (living room side) of an internal wall (shared between the bedroom and living room). We had the DPC reinjected and the wall was replastered.
90% of the new plastering has dried, however I still seem to have a series of patches that have not dried (its been about 10 weeks), the patches are at the sites of the original damp, one of the patches has salts forming.
One of the patches also appears to get worse after it has rained etc (even though it is on an internal wall).
Also on the other side of the wall, about 1m up the wall three wet patches have appeared (there are no salts), the patches seem to come and go, but they do not correspond to the damp patches on the reverse of the wall.
The wall is not cavity and is about 20-25 cms thick.
Has the new DPC been installed correctly?
Is salting of new plaster after a DPC/replaster normal?
You say you are a lower flat. Could it be a water leak from the flat above? I say this as a victim of such a leak: a slight leak from a washing machine upstairs over a long time was never noticed because it didn't cause pools of water, it just 'disappeared' into the floor / ceiling space. There will also be pipes crossing back and forth in the shared space which might have sprung a leak if mishandled or maybe even upstairs has had an ensuite shower put in! :roll: You need to talk to them: have they had any work done recently?
Yes, get an independent damp surveyor in to identify the root cause, make sure they have experience with old properties and go more in depth than just prodding a damp meter on the wall. These injections are regularly mis sold & are a useless in most cases on period properties.
If you get the area replastered again I would recommend specifying a lime plaster as the modern gypsum stuff draws moisture from the wall.
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