hi guys , i have just finished replacing victorian lath + plaster walls with 12mm wbp ply, ready for bathroom refurb . i am fitting a 1400 x 900 walk in shower enclosure with low profile stone resin tray . the corner of the room for the shower area is perfectly true and level and corner joints bedded and sealed with silicone . i am using a waterproof adheshive and waterproof grout so will i need to tank the shower area ? any advice greatly appreciated , cheers ,Ray