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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    • CommentAuthorYanntoe
    • CommentTimeSep 2nd 2017
    Has anyone any experience concerning laying a 12mm slate floor on a cured limecrete floor?

    We did one last year and it was a nightmare. A big floor, around 40sq meters and the advice from the limecrete supplier was to use the same mix as the original floor. Didn't work. Slates just would not adhere to the floor. We wet them, buttered the backs, changed the ratios and ended up with a sharp sand/ builders sand/ NHL 5 mix which just about keeps them down. To ensure some longevity they are pointed with off the shelf tile grout.
    And yes, I know that slate doesn't breathe especially when used with a cementitious tile grout.

    We're committed to slate for the next floor and, despite advice from lime suppliers to just use a cementitious floor adhesive, I'd like to use a breathable adhesive and leave wide joints, grouted with a breathable grout. We can increase the bedding depth as we have plenty of depth on the new floor.

    Anyone any suggestions?

    In anticipation .... thanks.

    • CommentAuthorYanntoe
    • CommentTimeSep 2nd 2017
    Oops, missed the dimensions which are;
    - the floor is 2 meters by 10 meters,
    - the slates are nominally 12 mm thick, 400 mm wide and random lengths, 500mm to around 1100 mm.
    • CommentAuthorowlman
    • CommentTimeSep 2nd 2017 edited
    Why not adhere the tiles on a floating decoupling membrane? Or, if you are a bit worried by the idea of a floating stone floor, most are, then just use a glued down decoupler in the more usual fashion.
    Personally I dont like buttering the backs of tiles especially long ones, ideally they need a continuous bed of adhesive.
    P.S. Did you prime the floor first??
    • CommentAuthortony
    • CommentTimeSep 2nd 2017
    Lime mortar and lime grout for me
    The slate is too smooth, you need to create a physical key by scoring the tiles before laying them.

    Also was the slab finished smooth? If so i would use a pricking up coat, harled, on the slab so that there was a mechanical key on both surfaces.
    • CommentAuthorYanntoe
    • CommentTimeSep 3rd 2017
    What would the mix of sand and lime be? Is that builders and or sharp sand , e.g. Cardewmire? Should it be an NHL lime (3 or 5) or a lime putty?.

    I could score each tile, or use SBR to give it a key?

    Is there a proprietary brand of lime bedding mortar that anyone can recommend?
    What's the top level of the current slab looking like? Is it consolidated or is it dusting? And is it tough with aggregate showing, or smooth with lime?
    • CommentAuthorYanntoe
    • CommentTimeSep 4th 2017
    The top layer of the current slab would best be described as "tough with aggregates showing" It's not very dusty at all. It's been down for about 18 months.
    We've used nhl5 with a high silica sand to bed slates and they seem to have stuck (so far). However, we've used the same lime with a limestone based aggregate for our screed and it has dusted terribly. If we were laying slates with that, they would certainly have lifted.
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