Hey, this is my first time attempting to tile in my first home. Did a bunch of research last year and made some notes and decided to go for hardie backer board based on that research. Finally getting around to tiling my bathroom, have bought the hardie boards and they all have a slight bow towards the middle, even though they were stored flat in the shop and have been at my house (they must be manufactured that way?). The problem is, my plasterer has left the walls way out of plumb and I had planned to dot and dab the boards to the walls plumb with tile adhesive and then use mechanical fixings once the adhesive had gone off but this is gonna be hard to do with the method I'd planned as I'll need to tighten the boards before adhesive has gone off to try and pull these dips out of the boards. That would mean some how trying to put blocks on the wall in certain places at just the right thickness because the wall isn't consistently out, there's waves in it - it's going to be a right pain. I was watching some videos of kerdi board installation and because there's a slight flex in these types of boards, they can just dab them to the wall and then give them a tap with a mallet to flatten them. I'm thinking of switching to an insulated tile backer board instead but I'd designed the shower stud wall to take a 6mm hardie board (they allow you to do this if screw centers are <400mm) but I've not found any documentation that allows 6mm insulated backer boards in this situation. Kerdi will allow 10mm if joist centers are =<350mm. The shower tray is already sand and cemented to the floor and shower components fitted, so really need to use a 6mm board. Appreciate any tips. Thanks.