Flag patio install technique question

Discussion in 'Hardscaping' started by manfromearth, Jan 13, 2007.

  1. manfromearth

    manfromearth LawnSite Member
    Posts: 68

    A buddy of mine was telling me about seeing a guy installing a flagstone walkway using a technique I've never used. It is an interesting technique, but I'm a little suspicious of how it would hold up. This guy excavated and formed up the area to be done in flagstone. He tamped in 1.5" of gravel fines (8910) and then tamped in a 1.5"-2.0" mixture of 32 scoops of sand and a 94# bag of portland. He cleaned his flagstone and then wet the back of the stone as he sat it on top of the dry sand/portland mix. After getting the stone layed down and level, he came back with a conventional mortar mix to fill in the joints. I'm not sure if he did any wetting of the stone (with the sand/portland mix underneath it) prior to grouting, but I'm assuming he didn't. He told my buddy that he's done many this way. What do you all think about this technique?
     
  2. tthomass

    tthomass LawnSite Gold Member
    from N. VA
    Posts: 3,497

    I think he will be redoing many this way. The joints are going to crack. Maybe you'll be lucky enough to be called for the repair and can inform the customer that you have to remove everything and pour a concrete slab and set it in mortar.......the right way.

    It has basically constructed a dry lay patio and mortared the joints.

    32 scoops of sand for a 94lb back of portland = weak......no more than 20 scoops
     
  3. tthomass

    tthomass LawnSite Gold Member
    from N. VA
    Posts: 3,497

    I need sleep.....thinking vs typing and spelling aren't working for me tonight. haha
     
  4. Az Gardener

    Az Gardener LawnSite Gold Member
    Posts: 3,899

    We do lots of sand set flagstone patios here in the south. If you don't have the freezing and thawing of the north it is not much of an issue. I challenge you to show me any flagstone patio that doesn't have some degree of small spiderweb cracks. As long as they run along the stone and not across the grout line its not a problem.
     
  5. tthomass

    tthomass LawnSite Gold Member
    from N. VA
    Posts: 3,497

    Yes freeze thaw is different but wetting the stone and setting it down in very week mix.......you may as well be using Elmers glue.
     
  6. Az Gardener

    Az Gardener LawnSite Gold Member
    Posts: 3,899

    Hey, all I can tell you is it's the industry standard here and companies that I have worked for and owned have put down acres of flagstone on million dollar homes this way for decades. It may be weak in your opinion but that is not to say it does not work or does not hold up.
     
  7. leaflandscape

    leaflandscape LawnSite Member
    Posts: 241

    I can only see that technique working in warmer climates. The freeze thaw cycle in the northern states and canada would make short work of that installation.
     
  8. manfromearth

    manfromearth LawnSite Member
    Posts: 68

    I would think there are some "tricks of the trade" to make this technique work. For instance, it would seem to me that you are going to be using mostly large pieces of stone and that they would be at least 1" thick (maybe 1.5"-2.0" being even better). Am I right on that count? Also, when using this method, do you do any wetting inbetween the stone before grounting or do you apply the grout (I've always used a simple mortar mix for the grout) directly on top of the dry tamped down sand/portland mix? Also, is the 1" or so of tamped 8910 before applying the sand/portland mix appropriate. I'm currently building a fire pit with a half circle stone bench and small patio. I may want to try this method, but I'd like to be sure that if I do it, I do it right and it's going to be there as long as I'm alive (haha).
     
  9. tthomass

    tthomass LawnSite Gold Member
    from N. VA
    Posts: 3,497

    I understand the joints but this is where I am confused. I will explain on a large range for simplicity:

    Okay, we've got 12" of the base @ 32 sand to 1 bag portland.

    The 1" stone itself is wet and set onto the dry 12" base of sand/portland.

    Say the water on the 1" stone supplies enough moisture to harden 4" of base under the stone.

    The remaining 8" of base is still dry.

    I view this as a 5" thick stone set on dry base, moveable.

    Freeze thaw perhaps not a factor but it is as if traffic itself......I don't know, its just loose with mortared joints that I see breaking to pieces over and over. Is this an issue?
     
  10. Az Gardener

    Az Gardener LawnSite Gold Member
    Posts: 3,899

    You probably will think our method is even more bush league. We don't even use any Portland or gravel we just put down a bed of sand 2"-4" thick, tamp it down then just lay the flagstone on it. Then we grout the edges, on the outside edge we will have the grout mix go down 4'-6' and taper out. We never use pieces less than 1" thick and yes they are usually large 10"x10" being about the minimum size and 2'x 3' are not out of the ordinary.

    We do wet ours down but that is mostly to get the dust off as we cut every piece so they have smooth edges and fit together like a puzzle. Our biggest grout joint will be 1"-1 1/2" wide. No 5"-6" grout triangles where pieces don't fit together so well for us.

    We have two soil types here, hard compacted clay or very loose decomposing granite that holds no moisture. This is a method that works for us . I would caution you to stay with the industry standards in your area or at least experiment on a friend or family's patio with this or any new methods.
     

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