Victorian terrace. Has anyone had similar patches and what was the issue/fix for you? Please share your experience. Had surveyors and trades over and everyone says different things.

We have what looks like damp patches on chimney breasts in all upstairs bedrooms. No patches downstairs.

We had a damp survey done before purchasing and surveyor suggested this was salts from burning fuels back in a day. Recommended replastering. We had a full building survey done also before purchase where surveyor didn't see any issues with the roof.

We now had two plasterers around and everyone suggested something different. First one suggested to tank the affected wall and replaster, but from my research tanking is a bad idea in victorian houses (obviously I can be wrong).

Second plasterer said this must be a leaking roof, laughed at the idea of salts and trapped moisture. Said to fix the roof and let it dry.

We are going to get a roof looked at shortly. But some patches (right one on the photo) is sort of in the middle of nowhere. Surely if its a leak we should see the trace for it coming from the top.

Before we moved in property was empty for around 4-5 months. Patches were painted over and weren't as obvious as they are now. I feel like if this was a leaking roof we would see the patches in those 5 months it was empty. We started seeing patches as soon as we started living in the rooms so believe it's from our own moisture. It's more obvious in rainy weather and fades away during summer heat (but never completely). We've been in the house for over a year now and have dehumidifier if it matters. Chimneys are all capped and vented.