Mould on new Plaster boards

[revelation]

We had new plasterboards put in a few months back on a new extension (dot and dabbed).  Shortly after below a window, we noticed some mould growth, it is in one area and has become worse.

 

Over the past few weeks, we have noticed some mould growing on an internal wall close to the floor level and near a socket.  The house hasn't really had any heating on as it's not being lived in at the moment.

 

Is this something that can occur due to general moisture and we go ahead and just plaster over, or something more serious to worry about?

 

Thanks in advance.

Edited November 24, 2022 by revelation

[markc]

It can (and does) happen where damp is ‘sucked’ inwards by the dots and dabs, but why is the wall cold and damp? Is it a new build that hasn’t dried out or an old existing cold wall? As long as the wall is now dry, throwing plenty of heat into the build will sort it out but if there is a source of damp in the wall then it will continue and spread

[revelation]

7 hours ago, markc said:

It can (and does) happen where damp is ‘sucked’ inwards by the dots and dabs, but why is the wall cold and damp? Is it a new build that hasn’t dried out or an old existing cold wall? As long as the wall is now dry, throwing plenty of heat into the build will sort it out but if there is a source of damp in the wall then it will continue and spread

 

Its an old house which has been extended, I wouldn't have thought there would be any damp.  But cant say for sure, the heating hasn't been on yet.  But the mould under the window happened in july/august time