Hardie board issues other recommendations please

Discussion in 'Tilers' Talk' started by cha1n, Jul 1, 2020.

  1. cha1n

    cha1n Member

    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.
  2. cha1n

    cha1n Member

    Just for the reference for any future readers, as this has been nearly a full days worth of reseach, I think this might end up being useful.

    I'm going to return my hardie boards. Looks like awful stuff to work with, there's a lot of value in me being able to cut my boards in the same room they will be fitted in, whereas hardie board sounds like nasty stuff to cut and would have to be done downstairs and outside. The most cost effective insulated boards I've found are Marmox boards. They actually approve the dot and dab fixing method with dowels that go through the dabs into the masonry (use rapid set tile adhesive for the dabs, not gypsum board adhesive). The cores are waterproof, so they don't need to be tanked like some of the other boards I was looking at. Any thickness boards can be used on floors (they go down to 4mm boards), so I can use 6mm boards like I was going to with hardie and all my existing measurements will match. I plan on using 12.5mm on the dot and dabbed wall and 10mm on my stud wall which has <350mm centers and will 'wet shim' them to the stud to ensure they are plumb and flat.

    They recommend waterproof tape over joins that need to be waterproof and an alkali resistant tape with a 150mm tile adhesive feather over joints that don't. Their tape is pretty expensive but I found this stuff, which has the same spec but is loads cheaper https://mastabuild.co.uk/index.php?route=product/product&product_id=72. They also seem to have some sort of sealant/adhesive that they recommend using on butt joints between boards and to fill the expansion gap around the room perimieter - I'm not convinced that it's much more than sanitary silicone but it's only £6/tube, so I'll probably use it for what it's worth. Someone else might look at the chemical compound and decide to use something equivalent and cheaper. The fixing washers are quite cheap at £13/100 and I'm going to use stainless screws at £18/200 but you can buy any alkali resistant screws (cement can corrode normal screws).

    Hope this helps someone in my situation in future!

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