Inspired by this post:
For over a year I've been musing about installing granite floor tiles on top of an existing arborite counter-top. I've considered gluing and screwing plywood, one layer, over the existing arborite, and topping it with granite floor tiles. You've also used a Ditra mat, which I hadn't known about. Since, I am very impressed with the quality of your research and knowledge, and I would like your honest opinion.