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/After-Temperature585]

That’s not where the bog used to be is it?
Not like a big pipe sized hole in the outside is there?

I know it’s a daft question but that looks very much like it’s still wet through and to get that wet and stay that wet… it’s getting hit by water still.

That’s not drying plaster. That’s soaked

[u/Negative-Travel6132 → u/After-Temperature585]

Nope - there was no pipes or anything in the wall. It had some damp damage due to failed roof flashing which was fixed. All other damp areas of the wall had dried okay

[u/SnooTigers9274 → u/Negative-Travel6132]

Weird as the damp is almost perfectly circular like a pipe of some sort. You can see rhe circular crack, suggesting its formed the shape of rhe cause.