DIY Doctor UK DIY Forums

Hi everyone, great to be here, really appreciate any advice given!
So...when I moved into my flat a few weeks ago the decorators had painted over a corner of flaking coving in corner of living room...it started to get a flaky appearance again not long after and after coming back from a few days with the family there is powder all over the floor underneath the coving and a damp patch about a square foot in size...it is about a foot below the coving on the front wall with bay window...its hard to tell if the damp patch is radiating from above or below...
Any ideas on what this might be?? and how I might be able to treat it from the inside?
Thanks very much for any help! :)

It won’t be from below as rising damp will only reach around 30” from ground level.
It sounds like either a leaking gutter that is soaking the wall or more likely to be a bay window fault, especially if it’s a only a single floor high bay window with a flat roof.