alternatives to replastering

In one spot on our ceiling two patches of cracked plaster are hanging loose by one edge. Is it practical to try to glue the plaster back into place?

Is your house an old house?

I would just tear off the loose pieces and fill in with drywall joint compound. Then repaint.

Plaster, even when reinforced with horsehair, doesn’t have a lot of structural integrity. So what’s likely to happen is that eventually you’re going to get a heavy chunk of plaster crashing to the floor. One possible solution is to use plaster washers (or buttons), which are kind of perforated washers that you screw into the plaster and into the underlying lath. Then you skim coat over the washer and any cracks to hide it.

There’s a possibility of cracking the plaster even more when you do this, of course, and you may end up with some noticeable depressions or bulges in the plaster depending on your skill in covering things up.