We had mosaic turtles placed in our FG pool while it was being made. The way I understand it, a rubber mold is placed when the FG shell is being made. It's removed and the matching mosaic is glued into the shell before the final gel coat is applied. You can barely feel the tiles under your feet. I don't know how you would apply a mosaic to an existing pool. Seems like it would stick up and catch your toes.

Chris