Patching and Plastering - Ceiling repair - plaster over wallboard

I had a plumbing problem in an upstairs bathroom and now have to repair a fairly large hole in my kitchen ceiling. The ceiling is some kind of wallboard with about 1/2 inch of plaster over it (I'm guessing it was done in the 40s or 50s). The hole spans two joists. I was going to square up the hole, taking it over to the next joist on either side. Then sister a 2x4 to the joists so I could use 1/2" sheetrock and have the surface even with the old ceiling.

Do I need to put a cross member in where the old meets the new?

Also the old ceiling goes all the way to the wall behind the cabinets. There is a plywood facia between the ceiling and the cabinets and of course the hole goes right up to that. What would be the best way to handle that joint short of removing the cabinets and facia?

Thanks
Bill Van Dusen

A cross member, when a repair only fills the cavity between two joists does help some to prevent the sheetrock from sagging in the middle, especially if steamy vapors are up by the ceiling. If a repair crosses 3 joists, then the need for a cross member is reduced to ...well, in new construction, when sheetrock crosses studs or joists, they don't put in cross members. They simply rely on the strenth of the tape to hold the abutting joints true to each other.

You may want to use fiberglass mesh tape in case you get a few little water dribbles up there in the future. Paper tape will wick the water terribly. I have done many ceiling repairs under bathrooms, and you can have this small leak where a relatively small area of sheetrock or just the paint got damaged...only to see where the water got into some nearby paper tape and blistered it for like 4 feet.

Regarding what you call the fascia, and what is commonly called "soffit": Do your ceiling joists run parallel to, or perpendicular to this soffit? IF they run parallel to it...how far away is the first joist from the edge of the soffit?

The joists are perpendicular to the soffit. There is a small cove moulding up there. I was going to remove that, clean up the edge of the hole as best as I can, then treat it like any other inside corner. Would that be the proper procedure?

thanks,
Bill Van Dusen

Yes. Fine. Now I have to go back and clean up my post above. Wow..the typos.