Tiling bathroom floor with Hardiebacker, electric UFH and self leveling compound

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Am doing my loft bathroom floor and wanted to confirm my order of flooring build up is correct?

-22mm chipboard
-12mm Hardiebacker, glued down using tile adhesive and 12 screws per board. 3mm expansion gap around perimeter of floor, which I'll fill with silicone (so there's no gaps when laying SLC)
-Electric underfloor heating - does this need to be glued down with tile adhesive or is it OK to roll out the self adhesive mat directly onto the Hardiebacker boards?
-Self levelling compound
-Tile adhesive and tiles

Chipboard is already in (glued and screwed) so will be doing hardie backer onwards
 
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Yes that all sounds fine. If you want better performance and faster warm up times from your UFH you could use insulation boards such as Marmox instead of Hardibacker, 10mm would be fine. Remember to prime each layer with tilers primer before starting the next. The UFH mat doesn't need laying in adhesive, there are strips of adhesive tape on the underside of it. My choice of levelling compound would be Mapei Ultraplan Renovation Screed. Good luck.
 
Yes that all sounds fine. If you want better performance and faster warm up times from your UFH you could use insulation boards such as Marmox instead of Hardibacker, 10mm would be fine. Remember to prime each layer with tilers primer before starting the next. The UFH mat doesn't need laying in adhesive, there are strips of adhesive tape on the underside of it. My choice of levelling compound would be Mapei Ultraplan Renovation Screed. Good luck.

Many thanks. I'd already purchased the Hardiebacker boards so will likely just crack on with those rather than insulation board - plus UFH will be a secondary heat source anyway so doubt we'll use it much

Just to clarify, when you say to 'prime each layer with tilers primer before starting the next' - which layer/s are you referring to? I assume on top of the SLC, before laying tiles? Would I also need to prime the chipboard before laying hardiebacker? And any specific primer I should be going for?

Also below link is the tile adhesive I'll be using (Mapei Maxi S1) to lay tiles onto SLC and lay hardiebacker onto the chipboard, this alright?
https://www.tilemountain.co.uk/tile-adhesive/p/keraflex-maxi-s1-grey-slow-setting-adhesive-20kg.html
 
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Since you'll be using Hardibacker it will be fixed with adhesive and screws so I wouldn't worry about priming the chipboard. Prime the Hardibacker prior to the UFH and you'll get the mat to stick down better. Also prime the levelling compound before tiling. Your adhesive will be fine. It's better to use the same primer as the adhesive so in your case it would be Mapei Primer G, although any acrylic primer or SBR will do the job, just don't use PVA. Good luck.
 

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