I have been practicing skimming onto some scrap pieces of plaster
board which I have taped together and temporarily fixed to a wall.

I'm using Thistle Multi-Finish and was hoping for a few tips.

1) One coat or two ? From other postings in this group it would seem
that you should apply two coats in fairly quick succession. This will
increase the time it takes to dry out and give you more working time.

2) How long to wait between applying the second coat and starting to
polish ? Does this just come down to experience ? I probably waited
about 1/2 hour.

3) When you are polishing should you be using the trowel flat against
the wall or at an angle ?

4) During the polishing I seem to keep ending up with a small amount
of sludge on the trowel which constantly needs to be cleaned off. Is
this normal ? I am keeping the trowel wet and using an old paint brush
to dampen the plaster on the wall before polishing ?

5) Does the plaster change colour once it's polished ? Seemed to turn
a bit darker after a few passes of the trowel.

Any help is much appreciated. The ultimate aim of this "practice" is
to skim a plasterboarded ceiling. Is this much more difficult than
working on walls ?