After taping the joints with scrim tape they need a thin coat of gypsum over the tape.
This needs to be as flat as possible and can be smoothed off with water while being applied.
The downstairs loo.
After the gypsum has been applied the DG27 primer needs to be applied over the whole surface. The DG27 not only provides a key for the plaster but helps control the suction of the boards - preventing the moisture being taken out of the plaster too quickly.