Hi, I am extending my bathroom to fit a 800 mm shower tray (taking some space from landing). I was planning to build a frame to surround the tray with 4 x 2 and then use 12mm hardie backer to line the walls of the shower area. The tray is a resin tray which I plan to sit on the floor. Would the hardie backer sit over the tray and then tile? or down the side of the tray and just the tiles overlapping the tray? . Also what would be the ideal centres spacing for the hardie backer to ensure maximum strength/rigidity? Thanks in advance