Some walls have plaster repairs to knee height (damp remediation 20 years ago) and the join between old and 'new' plaster is poor e.g. 2mm rim in places. It was hidden under wallpaper. I used Easi-fill on a couple of walls to smooth over. Looks nice. But I did not treat the surface first, just sanded, then wet with a water spray bottle. Is this a no-no? Will it come off? I have more joins to do on several other walls, and this time I will apply a base coat if needed. What should I apply after sanding the plaster? I assume that in the case of holes that such preparation is not needed.

these fillers are designed to bond to the paper on plasterboard which is low suction and to dried easifill when doing several coats, which is high suction.

I have always assumed that easifill can be used on walls of any description, although introducing more water may dilute , and therefore weaken, the filler. That said, it is often used dilute on cornice and we never have any problems.

Deep holes should be filled shy with filler that doesn't shrink, then finished with easifill for its ease of rubbing down.

Thanks. Yes I wondered about deep holes.