I used 3E clear silicone adhesive for windows and doors. (although it didn't turn out as clear as I would have liked) and I attached a flattened spoon to the back so I could mount it on a piece of conduit pipe from the hardware store that was cut to the desired height.
Mosaic Garden Stones - Inspiration. Glue everything down with a silicone type of adhesive then grout. Laticrete - SpectraLock Stain proof "Epoxy "Grout. It has 3 parts a are liquids and c is the powder color.