Some people like to hang a mirror, while others like to glue the mirror directly to the wall. Often, after a mirror is glued to a wall, a frame is put up around it to make it more pleasing to the eye. Mirror adhesive creates a very strong bond, and if you have to remove the mirror, you are in for a difficult task. Once you are able to remove the actual mirror, you will still have to deal with the adhesive that is stuck to the wall.
Apply a liberal amount of white spirit to the mirror adhesive. Allow to set overnight.
Scrub the adhesive with the scrub brush. Use a back and forth motion with firm pressure. The white spirit will not remove all of the adhesive, but some will be removed and the remainder will be loosened.
Place the heat gun about one inch from the adhesive and hold for 30 seconds. The heat will help to soften the adhesive.
Hold the plastic putty knife at a 45-degree angle at the edge of a glob of adhesive. Push forward while pulling up. The adhesive should pop or pull off. Continue until all the mirror adhesive is removed.