Ugh, I feel you pain. This is what I was dealing with in our recent bathroom. Here is what we did.

We had a whole a little bigger than yours. DH cut a rectangle out and pieced in a larger piece of drywall. I did not prime or paint before taping.

If you are a beginner I highly recommend No Coat for the corners. Yes it's more expensive that regular tape, but gives you nice straight corners with a lot less coats.

I will confess that I gave up on getting the ceiling smooth. I had part plaster, part old drywall, part new drywall. While I know I "could" have gotten it smooth, I was not happy in delaying the bathroom. I did a knockdown texture on the ceiling. It took me less than an hour to do, and you can't see the seems at all now. I did not paint or prime before doing the knockdown.

I don't know about you but I was very happy to see that old ugly cast iron stack gone.

Thanks BarbC. I will even that hole out and start from there. Yes I am so happy to have that pipe gone. It was a bear to clean around. It was kind of cute though. It had a real honest look about it :)

First you need to cover the 2 hole. You need to attach the replacement piece of drywall on the big hole to something solid before mudding and taping it. 2 choices are to open up the hole larger until you have some wood to attach it to or improvise! My favorite way to improvise is to cut 1 or two thin boards about 2-3 inches wider than the narrow width of the hole. Stick it up the hole the long way and rotate it so it is resting on top of the hole with about an inch on either side. Hang on to the board in the middle through the hole and put two screws up through the ceiling on either side of the hole to hold the little board in place. Screw your new piece dry wall into the little board(s) you put up there. Tape and mud.

Can't tell how big the little hole I but I would probably jut dry to put a piece of mesh tape over it and mud. If it sags you might need to put something up there to back up that patch too or purchase a firmer patch to go over it.

No need to prime anything until you get all your mudding and sanding done.

Use a putty knife and scrape as much loose paint away as possible. I would do little to no sanding of the paint edges as you are sanding paint with lead. Just skim coat everything with mud.

Patch, tape your corners, mud everything (couple thin coats) and sand. Then prime and paint.

Your joint compound will be perfect for all. Wear a dust mask when you sand.

Hags00, that small hole will be no problem, its smaller than a quarter. I used that picture to illustrate the paint and plaster edges. The larger hole, I think I will use your technique for the larger repair, or a variation of that.

I read some where that plaster did not take well to joint compound. It might have been something about drawing the moisture out of the joint compound too quickly for proper curing of the JC. I believe that was why the Gardz was recommended on the plaster, to provide a surface for taping the two materials at the junctions. Sounds like you haven't had problems with the 2 differing surfaces when taping.

No I haven't, my current house is plaster and I tore out the soffits and 2 pocket doors in the kitchen and then had to match new drywall to plaster and didn't have any trouble. Good luck with your project!!