"Andrew Gabriel" wrote in message
...

Generally, when joining plasterboard I suggest that where the two
pieces are fixed to the same support along the edge, you butt-join
them. Where they are not fixed to the same support along the joining
edge, leave a 1/4" gap and force bonding coat right through to form
a snot or nib (depending which part of the country you live in) oozing
out the back and the gap filled. This will bond the plasterboard
edges together rather well. Then in either case, tape scrim across
the join and plaster over with a finish coat.

--
Andrew Gabriel

Andrew Gabriel,

do you know whether your bonding plaster/nib technique would be useful
for repairing persistent cracks in an existing ceiling (cracks that run
along the edges of the underlying plaster boards and at rightangles to
the joists)?

The plaster boards were originally close butted together. I was
wondering about opening up the width of the crack to around three
millimetres by using a Rotozip type of tool - the bit diameter is three
millimetres. Would forcing bonding plaster through this gap, followed by
scrim and reskimmimg of the ceiling be likely to make a good repair?