Answers (2)
A mirror consists of a reflective surface stuck to the back of the glass and covered with paint. A wall is usually painted or papered. So you are talking about gluing paint to paint or paper. I once glued a hanger to a wall and hung a souvenir plate to it, and the hanger came of with a layer of paint stuck to it. The plate did not survive. The other problem you run into is how in the world are you going to unstick it when you decide to hang something else there?