I'm installing a prefab granite countertop that I've cut into several pieces for a jacuzzi tub surround and shower seat in my master bath. I'e cut the pieces so they fit together tightly but am not sure how to glue/cement in place. I've got a 3/4 plywood deck around the tub cut-out and used 1/2" plus 1/4" hardibacker for the shower seat with a piece of Kerdi waterproof membrane over that. What do I use to fix it in place? Is it the same for inside the shower as around the tub? Also, the slab thickness was not uniform. What do I use to raise the thinner pieces slightly to be the same level as the thicker pieces? Thanks for your help.