Hello. Decided to do some DIY. had a leak in my upstairs bathroom. And had to replace some of the plasterboard on the ceiling. There is now a 2 to 3mm step from where the new plasterboard and the original ceiling meets. Do i just put scrim tape and skim? Or skim up to the edge of plasterboard and then scrim tape? Totally new and thought i try my had at skimming. Everyone has to start somewhere right? Also do i prep the original painted skimmed ceiling with pva for 24 hours before skmming?