The actual glass weighs about 25kg. The wall is a freshly re-skimmed lath-and-plaster job and is pretty solid; I was thinking of sticking the mirror to the wall with some form of adhesive (probably standing it on temporary battens screwed to the wall until it's set). Using screw fixings would be awkward because (a) I haven't got the bottle to drill holes! and (b) the positioning of the holes relative to where the supporting studs are would look crap.
So - never having tried this before, is that appropriate for adhesive? What to use?... not sure there's any particular need for special mirror adhesive (unless that's best anyway) in that the back face of the mirror is protected by nylon-thread reinforced plastic film (for safety, from when it was a wardrobe door).
Should the plaster be treated first? With what?