"Brian Sharrock" wrote in message
...

Can you, please, expand on that? What packers, where? I'd assumed that dot
& dab techniques just plonked sufficient plaster to permit the board to
be 'plumbed'

When you dot & dab, it is almost impossible to cut the board to the exact
height needed - if it is too long or the ceiling is a bit out, the board
will become wedged and you'll never get it back plumb and straight. If it is
too short - you will have no way of lifting the board to create a tidy
ceiling line.
I was a dot & dabber for about 15 years (till back went) and always used a
1/2" offcut piece of board under the board to enable a board lifter to be
inserted to jack up the board tightly to the ceiling after levelling and if
necessary adding packing pieces - hardboard or asbestolux offcuts, nails,
screws or anything to hand to create a tight fit.
Of course you have to be careful about skirting fixings so only use the
minimum packing necessary to enable a board lifter to be used.