How to fix seperating plaster cracks
We are still working on the plaster restoration of this 19th century house in the black hills. We have some areas where the plaster is sagging from the lath. I thought this would be good to share. 
Step one is to find a drill bit just slightly smaller than the head of a drywall screw.
You then drill holes about every 4 inches along the crack on both sides. You must take care to only drill through the plaster and not the lath. Also if you miss the Ladd move over and drill another hole till you catch it. If the crack is quite loose you may want to drill every 2 inches. You then vacuum out the holes and apply adhesive with a caulking gun. We used gorilla glue.
Next you go back and put a screw in each hole making sure to sink it just below the surface of the plaster.
You can then let this sit for 24 hrs before applying web tape and bonding adhesive. You are now ready for plaster.
I never imagined I would find another Plasterer on Steemit, this is great.
I never liked putting veneer plaster over old lath and plaster because I didn't trust the substrate. I would do it after I advised against it to cover myself. You can't guarantee what you can't see. One option would be screwing new blueboard over the old plaster and just bury it. But invariably we ended up using Plasterweld, screws, and mesh tape over the old plaster, using a basecoat under the veneer plaster, similar to what you're doing.
This is my first round of doing this. I have overhung and finished plenty of times but I have never done a veneer coat over old plaster like this. But ya no guarantees.
My expertise is drywall and metal framing but spent a few years working with an old master plasterer Who taught me just enough to make me dangerous.
Love the STEEM!
I remember those old guys too. When they went they took a wealth of knowledge with them.
nice information .