Hi Dutchy,
I am not sure of the spec. It was approx 2 to 2.5 inches thick with a foil backing to it. Ciaran used circular bolts (inch wide) which were drilled and then knocked into place. He used fibre glass mesh on the joins and where the bolts were. They then skimmed all of the plaster board. On the inside edges of the windows he used single ordinary plasterboard.
I have some small peices of the plasterboard around I could email a photo to you.
The quotes I had from all the local plasterers were talking about slabbing the boards and putting tape on the joins. Skimming was going to be extra.
When I went for a quote from all of the plasters including Ciaran, I explained about the condensation and asked them to recommend a course of action.
Also barr two, none of the 6 plasterers who quoted I would have felt comfortable with in my home.
Give Ciaran a ring (I have no connection whatso ever with him) and he will be able to advise you. He is based in Leixslip.