I used this stuff when I did my kitchen -
http://www.dulux.co.uk/products/info/plaster_sealer.jspNo real idea as to how good it was. I had the 1st metre from the floor rendered. The render mix had some Cementone No2 & PVA added before application. Above 1 mtre to the ceiling I just dabbed & boarded.
Everything was then given a plaster skim and allowed to dry out.
Following this, the room was painted with this plaster sealer stuff and allowed to dry out further, then emulsioned throughout.
What I can tell you is that the plaster skim over the rendering began to crack off and flake away within a month or two of completion.
So when I got the plaster back to do the bathroom I asked him to reskim the damaged areas. These have since cracked and flaked again.
No idea what caused it. Initially, I wondered if the underlying render hadn't completely dried out, and that it had shrunk away from the plaster skim.
Other than this, I could only suspect that some chemical reaction had taken place between the waterproofer, the plaster sealer or the PVA.