In article ,
"Kevin Brady" writes:
Sorry - also meant to ask: Could I simply have another attempt at a very
thin skimcoat on top of the previous one - any preparation needed over fresh
(one week old) plaster?

You would need to do the two coats of dilute PVA first.
However, unless you know how to do a better job than
you did last time, there doesn't seem to be any point
(not meaning to be nasty -- just stating the obvious;-).

--
Andrew Gabriel