cutting holes in lathe and plaster

just went to suss a job today, cutting holes in ceilings for air con outlets. Problem is that owner thinks ceiling may be lathe and plaster !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!. ALARM BELLS I've worked with this stuff before and know its not to be disturbed if at all possible but they want it done and it looks like it has to be me. Has anyone got any really good tips for dealing with this prob ( besides running really fast ).
I have a 4" grinder and diamond blade ( dust !!!!!!! ) Sabre saw ( vibration - ceiling fall down velly qwik )
Also after suggestions for containing dust ( house is in Toorak- posh suburb in Melb)

Only thing I could think of Andrew is to drill four small holes at the extremities of the register and poke something up in the holes so as to see where they are up in the ceiling and then drill through each lath and then frame and nog out for the register and then screw each lath to the nog from below and then cut your hole out for the register and then charge them accordingly.

I agree with Bazza.......certainly charge accordingly.
When I was younger I saw a movie starring Yves Montard called Rififfi........about a bank robbery.....where they got into the bank from above, and did all that lath and plaster stuff too.
They stopped the mess by passing a closed umbrella through a small hole from above.......then unfurled the umbrella to catch all the crud and dust,
Probably useless information.......but a good memory jog.
Take the job..it'll be fun!

My suggestion is to cut through just the sand and cement without cutting the lathes around the perimeter. Then cross cuts to make the removal small chunks. Remove all the sand and cement from the laths.

Now cut the lathes carefully with a power saw.

By doing this you decreace the chance of a huge lump falling out where you dont want it to. Cutting the laths without the weight of the sand and cement with reduce the vibration and allow you to take more care.

If you are cutting between joists the laths may need to be supported from above before cutting! You could do this just using a strip of plasterboard and a very wet mix of cornice adhesive. Remove as much dust as possible before hand a little hand vac is good for that job.

Provided there is no drumming areas of lose plaster taking these precautions will allow you to cut the hole out without causing other damage. If the ceiling has lose drummy plaster to begin with your client should be advised of the risk and accept that large sections of the ceiling may fall out in which case the entire ceiling shoud be replaced in any case.

Good luck with it.

thanks every one, yep its those loose drummy bits I'm worried about too Rod !!!!!!!!