This is a job which could go very wrong, very quickly. I wuold check over at the expert tile forum, www.johnbridge.com for advice.
Help! I have a client who want's the walk way around the pool re-tiling, however he does not wish to remove existing tiles. This in its self is not the problem he wants a 2" fall to the edge of the pool which is too much to build with adhesive. how can this be done?