Damp proof advice

[Wetwall]

I've had someone do a job for me with tanking slurry in a spare bedroom. The room is upstairs. I've had him back twice with issues. Please can someone advice. Should the whole wall have been covered with slurry or just the circle in the middle that was wet? Is the white coating that dried on the plaster normal ? I was told to wipe it off and paint over it but had to get them back to fix where it was still wet this time he cut a small patch out to repair but the job doesn't feel like it's been done properly. Please someone advise what to do next

 

[Monkey Boy]

What is other side of that?