Hi - Im in the middle of refurbing my daughters ensuite (Jack and Jill), I don't plan to fit a wet room, but when you have teenage daughters im as well making it as waterproof as I can. I have removed all the plasterboard on the walls and replacing with Kerdi board, and I will seal appropriately around the shower area, I plan to replace the chipboard flooring with 18mm Marine Ply. I was going to use hardie backer board on top of the ply, then tile, but Im not sure that give me a good waterproof seal for the floor, are there any suggestions in what is best to waterproof the plywood floor? thanks