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Thinnest mortar bed you ever did under bluestone?

Discussion in 'Hardscaping' started by Ecscaper, Apr 21, 2009.

  1. Ecscaper

    Ecscaper LawnSite Member
    Messages: 23

    Hi guys,

    Over concrete, what's the thinnest mortar bed you've used to set bluestone?

    Usually I'll do a 2" thick stone around the edge and infill with 1-1/2" so I end up with most of the bed being about an inch. I do a slurry, then a real dry mortar bed, set the stone, pull up the stone, slurry the stone, reset stone.

    I have an existing stair condition where I have to add bluestone treads on top of existing concrete. Due to existing conditions I have to keep the mortar bed as thin as possible to keep the riser height reasonably uniform.

    What's the thinnest mortar bed you've successfully used? Has anyone used pre-mixed mortar with admix (think notched trowel)? I'm in a freeze-thaw area.

  2. riverwalklandscaping

    riverwalklandscaping LawnSite Senior Member
    Messages: 759

    if your adding a tread that is the same size to each step it shouldnt change the size of the rise? I mean if you add two inches to each step each step is two inches higher so its all the same in the end except the first/last step is higher by the amount of the tread height. Maybe I don't understand?
  3. Isobel

    Isobel LawnSite Senior Member
    Messages: 548

    i think what he's saying is that he wants to keep that added height on the first/last step to a minimum, therefore he's looking for the thinnest mortar bed.
  4. Ecscaper

    Ecscaper LawnSite Member
    Messages: 23

    Yes, the landing at the bottom will not be getting anything applied to it. Two steps and the third rise (to the upper landing) will be getting bluestone.

    The first rise is short, so I can hopefully add a tread to the step and keep that first rise <3/8" higher than the rest.

    If I could use premix mortar+admix I could probably keep it in the range of 3/16.

    3/8 is not really that much, until somebody trips :) I try to keep the rises +-1/8

    How thin could you realistically go with type s? A normal bed is 3/8", I'm wondering if I could go thinner without popping.
  5. 2low4NH

    2low4NH LawnSite Bronze Member
    from NH
    Messages: 1,890

    dont go under 1/4" you can not use thin set with a notched trowel it will not hold. i try and keep a minimum of 1/2" under my bluestone. if you stay closer to 1/2" it allows more play time to set the stone. do not pick the stone up after you have set the stone it breaks the bond and makes it weaker every time you move the stone.
  6. Ecscaper

    Ecscaper LawnSite Member
    Messages: 23

    HI 2low,

    Thanks for the reply. Yeah I didn't think 1/4" would work. I know they make the pre-mix+admix mortar for doing tiles outside. Wasn't sure how bluestone would work with that stuff since the stone is porous.

    I've always used the pick-up-reset method. I use a real dry mortar mix. I make a real loose slurry with the mortar (like the thickness of heavy cream) and apply that to the the stone with a stiff brush.

    The slurry forms the bond between bluestone and mortar when I reset. It seems to work well.

  7. 2low4NH

    2low4NH LawnSite Bronze Member
    from NH
    Messages: 1,890

    yeah slurry mixes will help. i tend to try and set in one shot. if i can. i do slurry mixes on dry face natural stone work on fireplaces to make sure they are all bonded they work great. are you using any portland in your mortar mix? when your doing stair treads i tend to scar up the base of the stone a little to help with bonding. the stone we buy here is really smooth on the bottom. i live in a heavy freeze thaw area so bond breaking here is a huge problem.
  8. Ecscaper

    Ecscaper LawnSite Member
    Messages: 23

    No added portland here, I used Type S and some extra lime. Are you mixing your own mortar? What proportions?

    Anything that works for you up in NH should be foolproof down here!
    Last edited: May 1, 2009
  9. 2low4NH

    2low4NH LawnSite Bronze Member
    from NH
    Messages: 1,890

    2:1:1/2 sand portland and mortar. i very rarely use pre mix only when the temps drop.

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