Need help with flagstone patio

Discussion in 'Landscape Architecture and Design' started by JimLewis, Sep 10, 2004.

  1. JimLewis

    JimLewis LawnSite Fanatic
    Messages: 6,872

    Hey guys. I could use some help / advice with constructing a flagstone patio. I am working on a project for a friend of mine. I have a lot of experience installing flagstone patios where we put sand or fine gravel in the joints. But my friend wants the flagstone mortared in. I don't have as much experience installing mortared patios.

    I thought we'd be able to just install our base (1/4 minus gravel compacted with a vibrating compactor) and then install the flagstone, then install mortor in the joints with a mortar bag. I thought that would work. But my uncle (a general contractor) says that will look nice now but come winter, when water and freezing temperatures effect it, it will begin to crack and by next spring it will look horrible.

    My uncle says that the only way to mortar flagstone together and make it work is to actually lay the flagstone on a 1" layer of wet mortar. Then we have to wait 4-5 days for it to completely harden, and only THEN can we mortar the joints together with a mortar bag. And finally, he suggests we seal the top of it with a water sealer to keep water out during the winter.

    So I guess if I have to do it this way, we will. The crappy thing is that we've been working on this for 3 days already and already have the flagstone all in place. I hate to take it all off and basically start from scratch.

    Short of starting over and laying the flagstone on wet mortar, is there any way to mortar the flagstone together as it is now? Anyone have good experience with this? I need to know by Monday, October 13th.
    Forest likes this.
  2. kris

    kris LawnSite Bronze Member
    from nowhere
    Messages: 1,578

    Jim ...this was many moons ago but your contractor friend is correct IMO.

    We poured a base of concrete,then we laid it on about an 2.5cm of wet mixture .

    Since your time is limited working with the wet mixture we did what you have now. Remove them and number-place them beside the working area the best you can.

    If you decide to not go that route i wouldn't bother with trying to mortar them together....pack in stone dust or something similar...perhaps with a bit of concrete so it firms up real tight.
  3. GreenMonster

    GreenMonster LawnSite Silver Member
    from NH
    Messages: 2,702


    In reference to above, polymeric stabilizer sand might work. It is very fine and hardens up when water is applied. It's typically applied to pavers, so I'm not sure how it would work in larger gaps. It's also expensive $12/65lb bag.

    Little mortar work around here like that due to frost.

    good luck.
  4. D Felix

    D Felix LawnSite Bronze Member
    Messages: 1,898

    You want to ship some out here?? That's cheap, the price list from one of our suppliers has it at $21/65 pound bag!

    Sorry Jim, I don't have much experience with mortaring flagstone, but how your uncle said to do it is how I've seen it done around here. Pour a concrete slab, and mortar the stone to it.

  5. Gilla Gorilla

    Gilla Gorilla LawnSite Senior Member
    Messages: 923

    Dan try $23.95 for a bag of that stuff in northern virginia where I get my stone and dust from
  6. JimLewis

    JimLewis LawnSite Fanatic
    Messages: 6,872

    I LOVE the idea of polymeric sand. The cost really doesn't matter. It's the savings in labor that I am interested in. I've been doing some searching on the internet - trying to see if polymeric sand (aka "stabilizer sand") would work on a flagstone patio application. Still researching that.

    One product I found is VERY promising! EnviroStone by EnviroBond This is just a landscape supply company's website. The actual website for the manufacturer is But I like the detail the first site has.

    Only problem is that there are no suppliers of this product anywhere near where I live. So the search goes on......
  7. Turf Medic

    Turf Medic LawnSite Bronze Member
    Messages: 1,073

    Haven't tried it yet, but it is my understanding if you want to mortar flagstone in, you first lay concrete under the area you are going to flagstone, similar to pouring sidewalk, 3-4" thick, let that cure out, then attach the flagstones using a layer of mortar, plus filling the areas between the flagstone. Not a bad job, but really sucks since you have already done a lot of prep work that won't work for the application you are wanting.
  8. JimLewis

    JimLewis LawnSite Fanatic
    Messages: 6,872

    The flagstone patio that we are installing has a layer of compacted 1/4 minus rock under it. Under part of the patio is a exposed aggregate concrete pad. But our new patio extends beyond that orginal pad. So the where there isn't concrete underneath, there is a good 6" of 1/4 minus that we compacted with a vibrating plate compactor. It's almost as solid as concrete. And I'm told that I can just lay the wet mortar on top of that and it would work.
  9. Turf Medic

    Turf Medic LawnSite Bronze Member
    Messages: 1,073

    Like I mentioned we haven't tried mortaring flagstone in, so I am not speaking from experience, only information, I was told that you needed a bed of concrete under it. Not sure if I understood the guy correctly but the objective is the mortar adhering to the concrete and the flagstone. He even mentioned using some sort of chemical to treat the concrete if it was older, to help with adhesion. This keeps the flagstone from breaking loose, and the seams from cracking. My guess is that the mortar will not work as an adhesive between the flagstone and the area that you have compacted, ie if you put mortar down on the compacted area, it will lift right off after it cures, whereas with concrete underneath the mortar you would have to chisel it off after it cures.
  10. GreenMonster

    GreenMonster LawnSite Silver Member
    from NH
    Messages: 2,702

    fwiw, the polymeric I've been using is from Techno-Bloc.

    Grey or brown.

Share This Page