Our house is a little over 100 years old and as such it has lath-and-plaster walls and ceilings. As it tends to do, the plaster has come loose in several areas, some large. The small stairwell leading upstars from the kitchen is narrow, and the plaster on the walls is afloat in large areas- you can push on it and it moves. I've been putting off repairing it because I figured I'd have to demo all the loose plaster, which would make an unbelievable mess. I finally decided to tackle it because I found a less invasive method (thanks, This Old House!) and I wanted to share it in case any of you are in the same situation. Drill 1/4" holes through the plaster, but not through the lath, in a grid pattern leaving about 3" between holes. Make sure that the holes go to the lath rather than into the void between laths. Vacuum the dust out of the holes and inject construction adhesive until it starts to back out of the holes- cutting the nozzle of the tube straight across rather than at an angle makes it a little less messy. In especially loose places you will see the plaster start to bulge out as the adhesive gets in behind it. In small areas, using fender washers and sheetrock screws (2" or so), screw the plaster down, running the screws into the holes you drilled to inject the glue. For large areas, I made 12" squares of 3/8" CDX plywood and covered one side with clear packing tape. This keeps it from sticking to the wall. After injecting glue I place the taped side against the wall and screwed through the plywood into the wall. It's working well so far, producing a fraction of the mess of demolition. Once I've got a large section done I'll start mudding and sanding while glue is curing in the next section.