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  1.  
    Our lime slab is dusting quite a lot. This hasn't happened with the other lime we've used. The aggregate is limestone based. I wetted it religiously for 2 weeks (maybe too much?)
  2.  
    I should have added, I'm not sure what might have caused it, or whether it is normal? It was NHL5 and has gone off extremely hard. Might anybody be able to shed any light on what might have happened?
    • CommentAuthorgyrogear
    • CommentTimeAug 1st 2017
     
    Hiya, CoP,

    wow, your slab sounds HARD !

    I used NHL 3.5 by Italcement

    but I mix it with loam (= muck form the crawlspace floor) (= half sand, half clay).

    the actual mix is:
    1 VOL OF LIME (“NHL 3.5”)
    1 HALF-VOL OF CEMENT (OPC)
    1 HALF-VOL OF FIRE ASH
    4 VOLS of DRY SAND
    NOTE: ONE VOLUME = 5 LITERS…

    MIX the above DRY in a trough
    then gradually trowel the DRY MIX into 12 LITERS of water (in an 80-liter black plastic dustbin…).
    Then mix thoroughly with a stick: it gives a sloppy mix with the consistency of a “semi-mousse”.

    Then I pour this onto the sub-base - here is a photo or two !
      After a trip to Trowel Services....jpg
  3.  
    Thanks @gyrogear. Looks very interesting! Yes, it is hard. Secil NHL5. It is deceptively hard. I thought it was a bit crumbly, but it is extremely difficult to chip away at. I wonder if the dusting is as much down to the limestone aggregate as the lime. Perhaps a more silica rich aggregate would have been less dusty?
    • CommentAuthorgyrogear
    • CommentTimeAug 1st 2017
     
    I guess that the dusting is a problem if you need to stick unglazed earthenware tiles to it ?

    I am wondering if your slab is actually suffering from efflorescence, if so, muratic acid can be used to remove
    it...

    http://www.concreteconstruction.net/products/decorative-concrete-surfaces/what-causes-efflorescence-and-how-do-you-remove-it_o

    Mick
  4.  
    Maybe, I'm not sure. I've seen efflorescence on concrete and this is not like that. Basically the lime seems loose on the surface, so that it can be brushed out, leaving more of the aggregate showing.
    • CommentAuthorgyrogear
    • CommentTimeAug 1st 2017 edited
     
    •  
      CommentAuthordjh
    • CommentTimeAug 1st 2017
     
    I believe its a common problem but I don't remember what the cause is, sorry. I'd suggest asking your lime supplier.
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