Mapei have confirmed over email and on screwfix that its fine to use to gypsom plaster as long as I seal with primer g. Bit worrying its not mentioned on the technical sheet.
Oh well just gotta wait for plaster to dry now. This one section that was a chase that has been filled in (with bonding i assume) doesn't ever appear to get any dryer, it is on the outside wall so understandable i guess but still would be good to see even a little progress
Thanks for the help above chaps, really do appreciate ur it.