What's going on on this wall - mould?

[mitya]

Hi everyone, first time poster.

This wall is plaster board. There's a cavity behind it, and the wall behind that is an exterior wall. It gets very cold. What does this look like (zoom in to see spots) - mould, mildew, or...? Further, what can I do about this - should I get someone round to advise on adding insulation between the plaster board and the exterior wall? Appreciate any help!

 

[Mrs Ten Names]

- should I get someone round to advise on adding insulation between the plaster board and the exterior wall?

Yes.

 

[^woody^]

Whether it's insulated or not is irrelevant unless you plan to rip it all down if it's not.

Deal with the conditions that are being created to cause the mould to form.

Sterilise the wall and apply an anti fungal paint.