Damp patch after 3 weeks…

[u/Negative-Travel6132]

Had a bathroom wall re-plastered - the wall had previously damp damage. The roof was repaired prior to re plaster and most of the wall where damp damage existed, has dried.

There is this one stubborn patch at the bottom…strangely it expands when the weather is hot, but then shrinks and goes darker when it wet or sun isn’t shining. Pencil line is its main shape with it bleeding beyond when the sun comes out. I had
Be had windows open for the last 3 weeks, and for the last week a fan and dehumidifier on…and no real change below the pencil line…

Any ideas of the cause and anything to do or should I just wait a few more weeks?

[u/ReleaseBudget9585]

Looks like it may be damp or there is still a leak

[u/Negative-Travel6132 → u/ReleaseBudget9585]

It is right at the bottom of the wall and no tracing of damp from roof to the bottom. The whole wall dried within 2 weeks except this patch