Dowels in friable plaster
Maybe some of the old people in the building know this: you are drilling a hole for a dowel; when you screw the hole breaks out, and a lot of plaster crumbles extra even with out - hole unusable!
Not quite. You can clear the hole from dust and carves a bit not to hard wood, in diameter as large as the hole, in length so deep. Put it in the hole (maybe deepen the hole a bit beforehand) and the screw should now hold in it. (Without dowels now, of course)
If necessary, some plaster to smooth it out.
