Mortar not sticking to paving slabs

Discussion in 'Builders' Talk' started by Melly, May 4, 2012.

  1. Melly

    Melly New Member

    Hi there,

    Can somebody please help me with my patio laying. I laid a few rows of slabs last week on a 2.5" wet mortar bed of 3 sharp sand to 1 cement with a plasticiser on a 4" MOT whackered base. It did rain 24 hours later but I did cover them up. I went to lay some more yesterday and realised that they were loose and not adhered to the slab at all, not one bit of cement had stuck to the slab and there was complete contact with no voids. I have bradstone ashbourne slabs and the only thing I did notice was that there is a shiny "film" on the back of them. The cement didn't really take to the hardcore that well either.

    I've got them all back up and am ready to start again but not sure what to do, should I add a hardener to they go off quicker, even though this doesn't really help with the adhesive side of things??

    Any help would be gratefully appreciated.
     
  2. Captain Leaky

    Captain Leaky New Member

    Why on earth would you use sharp sand? Building sand should be used. No need for plasticiser either. Also 6:1 is a much better ratio.
     
  3. Melly

    Melly New Member

    I thought it would be stronger....is that the problem then do you think??
     
  4. G Brown

    G Brown New Member

    You have done it all wrong! Use building sand in 1:6 ratio, no additives.
     
  5. Melly

    Melly New Member

    Shall I sprinkle any sharp sand in the gaps of the MOT first or just cement on top
     
  6. Melly

    Melly New Member

    Also forgot to say that some local builder told me to use 3 sharp, 2 building to 1 cement...I really don't know what to do for the best...??
     
  7. Building sand on its own is to soft and mixed at 6 to 1 is useless below ground, it will fail.
    Use a plastering sand or as your local builder said 3 sharp and 2 building, wet mix and full bed of mortar.
     
  8. Melly

    Melly New Member

    Thank you very much, I thought building sand alone would be too soft.

    Cheers :)
     
  9. DIYDave

    DIYDave Guest

    Hi Melly
    I laid a patio last summer with a friend and being a diy'er, did a fair bit of research before we started.
    Found a brilliant site with endless info on all aspects of paving - pavingexpert.com  (It's been recomended on this site many times)
    Not knocking any help that you may recieve on this splendid site but really suggest that you spend some time reading through pavingexpert and you can post questions as well

    I laid my slabs (after ground work prep) on a solid mortar bed of sharp sand / cement @ 6-1 with a bit of plasticiser in the mix

    There is a lot written on paving forums about slabs not bonding with the mortar bed and a lot of replies say that this is quite usual and not a problem, as long as you leave a gap between the slabs and then fill with mortar, this will then bond the slabs together

    Wanted my slabs to stick to the mortar bed (just seems a better job to me) so "painted" the back of each slab just prior to laying with a slurry mix of SBR and cement powder - they stuck like sh#t to a blanket and not a single rocker
    Then filled the joints, spaced at 10 mm, with a damp mix  and the slabs will never move

    Hope you find this helpful and read up on the above site - good luck
     
  10. Melly

    Melly New Member

    Thank you very much, I'll have a read of that too
     

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