Ceiling Repair

I have a very old (100+ years) house, and am having issues with the lathe a nd plaster ceiling in one of the bedrooms. The plaster has started to sag and is causing some cracking. The cracks are all hairline, except for the spot where all the cracks are forming from, which is a hole about 1/8-1/4 o f an inch wide.
Issue doesn't appear to be water damage related, but just from age/house se ttling.
After doing some research into the issue, it seems that my best course of action would be to put some screws into the ceiling to secure the plaster and then patch over it. I do have some additional questions:
1)Even though this is caused by loose ceiling, would i still need to score the cracks, and if so how deep will I want to go?
2)Do I need to score, secure, and patch all in the same day, or is this a p rocess that I can break up over 4-5 days?
3) Once I'm ready to patch, should I get some mesh to put down after the fi rst layer of patching?
4) What kind of patching agent should I use? I've seen DIY articles recomm end anything from all purpose bonding agent up to durabond.
5) Should I screw all along the cracks, or just where I feel loose ceiling?
Thank you all in advance!
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snipped-for-privacy@gmail.com writes:

Find the This Old House episode where they shoot glue into the plaster cracks before using the special screws.
--
Dan Espen

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When my son had some serious sagging and cracking (caused by a roof leak) we reattached the sagging plaster using plaster washers similar to these:
https://www.google.com/search?q=plaster%20washers
In our case the damage also required the replacement of some sections with drywall patches. After looking at the semi-finished job and the amount of skim coating it would have required to hide all of the washers and seams, we opted to add a layer of drywall over the entire ceiling and mudding the two seams in the field and the wall/ceiling junctions. It came out real nice and no more worries about future cracks.
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Before I did anything I'd want to make sure that the lath is in good shape and well secured.
--

dadiOH
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On Tue, 10 Sep 2013 11:07:36 -0700 (PDT), snipped-for-privacy@gmail.com wrote:

The plaster keys will continue to break. And the more you disturb the plaster, the more keys will break. I'm not familiar with using screws or glue to secure old ceiling plaster, so can't comment on its efficacy. When I was working with my brother, he used two solutions. Tear it down and drywall if it was bad. That's a permanent solution, and looks good. Or if the ceiling was basically solid and flush, cover it with 1/4" drywall. That's also permanent and looks good. Old woodwork you want to keep can complicate things.
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Red Green wrote:

Interesting. I had never heard of "plaster washers" before or seen that method.
I could see some problems with that approach in terms of getting the ceiling to be flat etc., but it looks like a good trick that would definitely be "good enough" in some situations.
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