I Have around 10m2 of spare IPE/Brazilian tropical hardwood unused from a recent deck I built. I'm in the process of renovating my bathroom and was thinking of using it instead of tiling in the shower area. I have the shower currently clad in 12mm cement-board. Pintrest and google display many examples of IPE being used in wet areas and from previous experience using it, it should not suffer from water exposure although it does expand and shrink quite a bit with moisture which I planned to combat with two coats of matt Poly. My plan was to tank the cement-board with a membrane and fix to IPE planks using fiber reinforced modified tile adhesive. I thought about battening it off and using stainless screws but i'm reluctant to have any kind of holes through the membrane even if they are sealed. Any suggestions welcome.