Damp upstairs wall

[Wetwall]

Hi would you use tanking slurry on a upstairs wall? I had work done about 6 weeks ago and where it was treated with tanking slurry dried with like a white chalk ontop they said that was normal and to just wipe it off with a wet cloth which I did. Then another part didn't dry near the top so they came back amd cut some out to treat that part but I can't help but feel like it's not been dealt with properly ? I don't have a clue what's going on now. I have applied a coat of white paint as I've been hoping to get the wall painted and finished. Here's pictures

 

[Wayners]

Get a summer fan in there to move air about. Keep it going as much as possible.
Open window a bit when the weather is dry.
Air movement is better than heat.
Thick plaster and closed room causing drying issues maybe.

 

[JessThePlasterer]

Is that an air vent? Could be they’ve used a damp brick and it’s taking a while to dry. Use a dry brush or cloth to brush off salts. Or if it was a vent, open it back up