asalcedo wrote:
What is the best way to repair hair line cracks on a lath and plater
ceiling?

The standard way, and what my decorator is doing at the moment, is
raking out, filling in and sanding down.

Don't. Just *don't*. Do this, instead. Get a squeezy bottle,
and C. 2" of foam pipe lagging. Clean the bottle. Tie lagging
around the neck (remove the nozzle first). Make sure the seal
is good. Get some 2" re-inforced waterproof tape, and wind it
around the lagging (to keep the split together). Cut off the
lagging/tape to make a flat surface at the top. Get some 5:1
water:PVA and fill the bottle. Push the flat surface of the
cut off lagging up against the crack, so that the lagging
makes a seal, and the hole in the middle straddles the crack.
Squeeze, and some PVA will go into the crack. You can sort of
rythmically squeeze the bottle, so that the PVA mix is forced
in with a sort of "donk.. donk.." sound. When the PVA is dry,
it will a) glue the edges together, and b) (important!) stop
the edges moving together, and allowing sand to drop through,
which knackers lining paper, forces filler back out, etc. Any
sandy stuff in the crack (ooh-er!) is a positive advantage,
as it will help fill the join. N.B. PVA mix is likely to drip,
so wear a hat, and wipe any drips off after applying the PVA,
or it'll show when you decorate. N.B. if you rake out the
joint, the PVA mix will **** out all over the place, and not
go into the crack properly. This will stick the whole flippin'
sealing back together. Mark out cracks with pencil before
applying PVA. If necessary, let it dry for 24 hrs. before
putting more in. I've used this method quite a lot, and it
really works (also on plasterboard joins, reasonably). For
cracks wider than hairline, use thicker PVA:water.