[Mirror Adhesive][1] ("*mirror mastic*") exists: ![enter image description here][2] As for how to hold it up; rest it on something: - the top of the backsplash - rest it on a strip of wood fastened to the wall and use mirror clips while it sets. [1]: http://www.rona.ca/shop/~adhesive-mirror-adhesive-mulco-414642_mulco_paint_shop [2]: https://i.sstatic.net/sJwk0.jpg