Hardibacker on Celotex/ Kingspan

Discussion in 'Tilers' Talk' started by Haider, Mar 21, 2020.

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Problem with flooring using hardibacker ... HELP

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  2. bathroom

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  1. Haider

    Haider New Member

    I have removed the old floors from a bathroom, around 5 square meter, and there was a celotex (50mm). It was sitting on a concrete slab. I repeated the same model, but I added a membering first then 50mm celotex then 12mm Hardibacker. I fixed the hardibacker with screws to the main concrete slab through the celotex. Any potential problem with that? Any advice before tiling?
     
  2. TonicUK

    TonicUK Member

    So, you put backer board straight on to Celotex which is sitting on your oversite? In essence the hardie is now the substrate... A general rule is that you don't tile onto substrates direct.

    Imo you should screed on top of the Celotex. Followed by self levelling
     
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  3. Haider

    Haider New Member

    Thanks for this, I put screws to hold the hardibackers to the concrete floor through the celotex (10 in each sheet), formed very solid floor. then I put the self leveling ( i can not add screed because i don't have much space .. Not sure if this is the best way
     
  4. TonicUK

    TonicUK Member

    Well, if you've already done it I would at least suggest to use uncoupling matting as there will be movement. Hopefully the hardiebacker suffices as a substrate equivalent to screed. 25mm of the screws you used going through the Celotex are basically wobbling around inside of the Celotex not doing much.
     
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  5. Haider

    Haider New Member

    To keep the hardibacker firm, I used 8 x 120mm screws, the hardibacker is 12mm + 50mm celotex, so it will be 55mm through the concrete with plugs. Like you said I will add uncoupling matt. Does it matter to tile with granite?
     
  6. TonicUK

    TonicUK Member

    Oh sorry, I said 25mm. I mean 50mm. Regardless, there is still 50mm flex in the screws inside the Celotex...
    If you are going to proceed with the way you have done it then make sure you use an adhesive and grout that is "flexible" for both the matting and tile.

    No matter the material of the tile ensure you use flexible adhesives and grout in your situation.

    If a client asked me to fit tiles on top of hardiebacker screwed down to oversite through Celotex I would not proceed without them signing understanding that there is risk of cracking tiles/grout.
     
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  7. Haider

    Haider New Member

    I asked the client to let me put the screed on top of the membering and to forget about the celotex to avoid cracks in the future with some joints on the sides. He asked me about the matting option and if it is a solution considering he doesn't like the mess of the screeding the kitchen. He asked me about the percentage of avoiding cracks if we use the uncoupling matt? anyone better than other?
     

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