I fully appreciate that the official line is to get it tested. However... It's extremely visible, it's very contained to a specific area (more on that below), and it's affecting 2 specific materials. So I thought the professionals in this forum might share any thoughts.
As per the photos, I've got a problem where white residue is building up on the wall paper of an exterior wall, and on the adjacent sofa that is (admittedly) too close to the wall. The wall is blockwork, probably with a plaster layer, and wallpaper -- classic uninsulated UK home. The sofa is maybe a microfibre or buffalo leather? Not sure... Not leather though.
The residue is spotty/patchy -- see the photos for what I mean. It's also dry (although I fully appreciate it's probably higher humidity between the sofa and the wall, which might feed whatever this is). If I wipe it, it comes off. But as I say, it's appearing on both the wall and the sofa, so I don't think it's efflorescence from the blockwork wall behind.
The problem is definitely contained to this area -- it's only behind the sofa, and the rest of the wall is not exhibiting this; and the problem has been there for years. It's only more recently spread so far up the sofa that it's visible on the top, and we're questioning how we address it.
We will definitely be replacing the sofa after we fix the wall; replacing it with one that allows more air flow behind.
https://imgur.com/a/FI5N1KF
