I have repaired a hole in plasterboard with new board. the size of the repair is about 40 cm each way but not a regular square. I plan to skim over the repair to level it off and then replace the tiles. The result must be watertight for since it is in a shower area.
Does the skim plaster go straight on to dry board?
Should I fill the joint between the old board and the new before skimming? If so what with? Is a building adhesive suitable? Scrim tape does not seem to be the answer because of the existing plaster up to the edge of the repair. The gap beween the edges of the board is from 0 to 3 mm. Part of the repair edge lies very close to the joints between the tiles so I am concerned that any flexing between the old and new board could compromise the grouting.