Yellow stains on walls

[Antoniyo1593]

Hi guys!

We have yellow stains in one of our walls.
There was damp at the bottom half of that wall which i treated the upper part doesn't look damp just have black spots. So plasterer came in and levelled that part with plasterboard adhesive and will comeback next week to properly plaster it. But now there's a yellow stain at the middle part of the wall, I've sanded it and it came back to white. So is this just condensation? Or is this damp underneath?

*Note we also don't have a cookerhood atm but have a dehumidifier

 

[JohnD]

water leak.

you can attach a photo by pasting it into your reply.

 

[Antoniyo1593]

I've checked for any water leaks already and I can't find any

 

[Antoniyo1593]

Sanded it down and yellowing disappears..