I posted a similar article on the plasterers forum and the negative response I got back was massive - its just a hot topic on there that myHammer must have threatened to sue them 'cos everytime the post goes up they have to bring it down! Good to see that we still have freedom of speech! For fun...
Just started trying to win more private business for myself, so after looking around thought that I would give myHammer a go! Anyway got an enquiry from them about condensation in a loft for £10! Thought to myself "you need roof tile vent - not my bag!" so trying to make the right impression...
Having no heating is not really be a factor in your case - this is only a problem if its near freezing - which by your timings it should not have been and the symptoms would look different.
The photos you have put up indicates that the problem is movement - either shrinkage from the joists...
I'd be inclined to ask your builder back and have a look at the problem. If he's reliable then he'll be able to give to give you a reasonable explanation. Looks very much like to me the joist were wet when they were installed and now they have shrunk pulling the ceiling with them. This could...
Looks to me to be a very bad case of shrinkage. Is there any scrim between the ceiling and wall joint? Was the surface the plaster applied to really wet before the finish went on?
Sounds good to me. The PVA will kill the suction in the blocks - they sound like aircrete blocks? so will have a very high suction which will make the plaster go off like a rocket! The PVA will also fix and dust - if there is a lot of dust then sweep it out first with a soft brush. With carlite...