Sorry I didn't get to your post sooner - I am sure you have worked things out by now. It sounds like the plasterers feel as though they have to do an extra special job for you - and this rattles your and their self confidence. If they care - which they obviously do - the job will find its way. It is the selfish know-it-alls to avoid in tradework.

You can't go wrong with the bonding agent between layers - although some of the museum conservation people feel there might be a greater tendency for the layers to separate if you had a long period of running water through the roof - a highly unlikely occurrence - unless a second flood is in the offing

Another reason I like the bonding is because I often try to introduce the cracking effect from too rich a lime, and the agent allows the cracking without sheets coming off - obviously this is tricky, and needs practise.

"The Art Bulletin" still discusses fresco does it not, but its pretty heavy goinf from what I have seen ? When I have time, I will practice a reproduction of a Giotto angel - have you ever applied real gold leaf (as a halo)? Thank you for your kind words but I assure you I have much more to learn from you than you will ever learn from me.