Tiling backer advice on masonry wall

I am doing a complete bathroom reinstall and was planning on using Hardie Backer boards for all four walls (three stud partition walls and one masonry wall). The problem I have is with the masonry wall, which I was planning on using dot and dab to fix the Hardie boards to. Hardie's own website says that dot and dab isn't an appropriate method for fixing to masonry though. The reason I wanted to use dot and dab is primarily because it will make it easier to make the wall plumb (removal of the old dot and dab has meant the masonry wall surface is now quite uneven in places) and also that I need to build the final wall out by a set amount.

Some context on the reason why I need to build the finished wall out by a set amount; I am installing some reduced depth fitted furniture against this wall. The tolerance of where the furniture can be in relation to the soil pipe (which is fixed) is wafer thin because of the reduced depth. This means I have this really tight tolerance of where the finished tiled wall surface can be in relation to the soil pipe.

So going back to the problem, I don't think I can use Hardie's suggested fixing method (adhesive glue and mechanical fixings) because the finished wall depth would not be enough. I can't add extra tile adhesive to accommodate as this would be more than the maximum recommended.

I have seen some posts on this forum saying it is possible to dot and dab Hardie backer, but it doesn't sit right going against manufacturer's recommendations. I have considered building the wall out with studs, but this would then make the finished wall greater than what I need for the reduced depth fitted furniture.

Additional info (if useful):

• Tile backer needs to be strong enough to support large-ish format porcelain tiles (600mm x 1200mm x 9mm)
• Dimensions for masonry wall are approx 1.2m x 2.4m
• Ideal finished wall distance from masonry wall needs to be approx 36mm to accommodate reduced depth furniture

Anyone have any suggestions or daft things I might not have considered?

 

Hi Jord86, thanks for the fast response

I think the problem with that would be the final distance from the masonry wall would be more than I need to get the fitted furniture aligned with the soil pipe. I was aiming for a finished wall distance 36mm from the masonry wall, doing what you suggested would push it out around 43mm (5mm minimum for the dot and dab, 12mm plasterboard, 12mm Hardie backer, 5mm tile adhesive, 9mm tile thickness). In reality, I think the dot and dab would be thicker than 5mm too to accommodate uneven wall surface, which would make that final distance even greater. The actual problem I have is the ridiculously low tolerance of the reduced depth furniture, but that's the challenge!

A bit more information on the furniture, the distance from the back of the front legs (which are required to clip the plinth on) to the back of the units is 135mm. Soil pipe obviously takes up 110 mm of that space which in an ordinary situation would leave 25mm of wiggle room (which is plenty). However, I also have to feed some copper pipe hot and cold feeds behind the soil pipe which adds on 15mm and reduces that wiggle room down to 10mm!

 

Although I guess swapping out the Hardie for moisture resistant plasterboard would result in my original planned thickness, which is what you have suggested. It's not a wetroom, so I don't expect that wall to really need the cement board from that point of view. Have you (or anyone had any experience of other backer boards that are 12mm and can be dot and dabbed and hold large format tiles?