Mould or something else?

[peeky1323]

Hi Everyone,

We have a solid stone house and over the last few years have removed the cement mortar from the outside side of the walls and repointed in lime. Some of the external walls inside have had the modern plaster removed and redone in lime or left as bare stone. A few of the external walls are boarded out (not by me). They are framed not dot and dabbed. I am unsure what insulation is behind but given the state of everything else won't be correct. We have a few "cold spots" where we get small bits of black mildew/mould on the cieling, I know what those are from the board being direct on the rafters. However, the issue I can't figure out is on a few walls there is a faint brown/tan spotting. It's even on a few internal walls. Does anyone know what this is in the attached picture? There is no smell of damp and moisture levels in the room are not high. Many thanks, Matt

 

[tell80]

The pic is pretty blurred.
"redone in lime" - do you mean a sand and lime render, or lime putty?
Do the spots appear on D&D walls or the S&L rendered walls? Or both?
On the ceiling can you see shadowy outlines of the ceiling joists "grinning" through the plaster board?