What is going on with my plaster?

[Rhiannon M]

we recently had our upstairs bathroom completely gutted. It all had to be replastered as all the walls were tiled floor to ceiling.
The walls have all dried ok apart from this one.
The pictures were taken today and this plastering was done approx 9weeks ago...plenty of time to dry. Note the dark patches, especially above the toilet.
This is an external wall. The shower used to be on it and the house was rented with no working extractor fan. The picture with the ceiling shows dark around the coving, this was an area that was affected by the shower and before redoing, the paint was peeling from (I assume) the condensation.
When we took the tiles off, the old plaster fell off back to the brick for most of the wall. Our local builder (who has done lots of work on our road) was employed to put the bathroom in from scratch. He used his own workmen and plasterer. I didn't note what exactly the plasterer did. I'm sure he skimmed most of the wall but sure what he did with the exposed brick wall. I don't think plaster board was used though, don't remember seeing any but could be wrong.
The house is 1930s with that awful pebbledash exterior, can see no cracks in it. Had the gutters cleaned out a few months ago, they are in good condition.
The dark patch has dried in the middle but is still there and I'm fed up. I want to finish the room and redecorate!
I'm a bit mystified as to why the damp patch is in the middle of the wall too. No pipes there or anything, has always had the loo there.
There is a working radiator on the opposite wall and the window has been pretty much open for the past 6weeks. It is quite a shaded room, only gets sun in the evening.
Any ideas? Thanks

 

[PrenticeBoyofDerry]

If the plaster basecoat was deep in those dark areas, they can take time to completely dry.
But if there was existing damp issues (not everything can be blamed on condensation), then that should have been rectified prior to any plastering work was completed.

 

[Rhiannon M]

Thanks, as far as I'm aware there were no damp problems. I guess I wouldn't have known as the area was tiled? So 9weeks could just be that it takes time to dry?
Thanks again

 

[Robbie uk]

Doesn't look to bad. Get a fan heater blowing on it for a while. Get a mist coat on and see if it re appears.

 

[Rhiannon M]

If it does reappear then do I need to do anything like sand off the mist coat from the area?

 

[Robbie uk]

Sometimes plaster just stays like that and doesn't look as if its dried although it may have. If it reappears, use a stain block or some oil based undercoat on the affected areas first, then coat up in your chosen emulsion after that.

 

[Doggit]

See if you can borrow, or buy a wood moisture meter (they're the cheapest ones). it'll give you a comparison against the light and dark patches. The plasterer may have used bonding to level out the walls, and as you can go onto that before it's dry, it does leave the walls patchy as the bonding dries out though the top coat of plaster. If it's still wet, and there's no obvious problem, then wait a bit longer. You could put a stain block on it, but that's not the most appropriate thing if it's still damp.