Hi, I need information on how to tape seams between new dry wall, old unpainted plaster, & painted plaster surfaces in my bathroom remodel. I have a hole to repair too where the old vent stack went out through the ceiling. In the pictures you will see where I peeled off old latex over very old paint from the 40's or so. I wanted to clean up where the taping joints will be. I have not sanded yet but plan to do so.

In reading the other posts on this topic I think it is recommended that I sand the painted ragged edges to smooth, and all over the painted surface to rough it up. Next, wash all painted and plastered surfaces with TSP and rinse well.

Then:
1) do I prime with Gardz, before taping?
2) do I prime the new dry wall too before taping?
3) Do I prime the whole ceiling before I skim coat (if I do this)?
4) How do I handle that hole in the ceiling? (I was going to use scrapes of drywall and mesh to cover, then mud it in place.
5) I bought the low dust blue lid joint compound, will that work for taping corners and ceiling junctions?

Any help would be great!

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.

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.

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.