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Sand or stone dust under bluestone?

Discussion in 'Landscape Architecture and Design' started by greenersideup, Jan 11, 2005.

  1. greenersideup

    greenersideup LawnSite Member
    from NH
    Posts: 1


    I am a landscape contractor who has been asked to re-do a bluestone walk that has failed. It buckled, and many of the stones are actually cracked. It is in NH, where the winters are long and cold. I thought maybe that the base wasn't done right, but we lifted a few stones, and found ~8" of gravel under 3"+ of stone dust. Do you think that the stone dust is holding too much water and didn't drain properly, and that's why the walk has failed? WHen we relay it, isn't it better to use masonry sand rather than stonedust?

    Thanks for your comments.
  2. cgland

    cgland LawnSite Bronze Member
    Posts: 1,929

    IMO the reason it failed is because of the stone dust itself....especially at 3"! Stone dust is poorly graded(meaning it does not have an even mix of small, medium and large particles) Stone dust consists mainly of....dust w/ some 1/4" pieces in it and because of that fact when you screed stone dust you can have highly concentrated areas of large particles and highly concentrated areas of very small particles, both of which settle differently causing waviness and/or improper settling. I would use coarse washed sand as a setting bed.

    P.S. just because you found 8" of gravel does not mean it was compacted properly.

  3. AGLA

    AGLA LawnSite Bronze Member
    Posts: 1,742

    Is the stone dust washing down into the gravel?
  4. AGLA

    AGLA LawnSite Bronze Member
    Posts: 1,742

    In the Boston area and down here on the cape, I have never seen anyone put stone dust over gravel. It is always stonedust only. The reason it is used instead of sand is that it compacts while sand does not (fire at will). I live on what is mostly all sand down here, yet stonedust is always used under bluestone when dry laying. We never had problems in the 'burbs from freezing and thawing (we do get freeze that down here from time to time on the cape as well). I walk on patios that I did twenty years ago that are just as flat and even today as they were then.

    I think that your best bet is to talk to local guys that have been around for a long time to see what they do.

    The concrete paver revolution has made construction standards for their products that a lot of people are applying to everything else as well. I'm not sure that is a good idea.
  5. northmichigan

    northmichigan LawnSite Member
    Posts: 133

    i build flagstone walks on 5oz.landscape fabric with 4 inches of 9a[crushed stone with dust also called road base] that is compacted and topped with an inch of diamond dust [stone dust] after i cut and fit the flagstone[one and a half inches thick stone] i sweep the joints with masonary sand to fill the area between the stones if the joints are wider than one inch i fill them with crushed stone.
    i can't say why your walkway failled but look to the drainage in the area.
  6. plantace

    plantace LawnSite Member
    Posts: 6

    Why do you use stone dust under but sand between the stones?
  7. northmichigan

    northmichigan LawnSite Member
    Posts: 133

    the stone dust makes a milkly stain on the flagstones when it rains. the masonry sand fills the joints and polishes the flags when you sweep it over the finished work.
  8. plantace

    plantace LawnSite Member
    Posts: 6

  9. steve in Pa.

    steve in Pa. LawnSite Senior Member
    Posts: 294

    The reason the stones are settling is the dust is lime stone dust. Which over time the lime stone chip or dust starts to break down and deteriorate. Farmers use lime stone dust to spread on there fields here in pa. Its basically a cheaper lime product. We see alot of that corner cutting or lack of knowledge for paver installation here. The dust is really cheap from the stone quarry therefore making more profit for the flyby nighters around here. ICPI certification states to never use dust for paver installation, they suggest concrete sand! We like it when we get calls to fix a patio or walkway that we lost because the homeowner went with the cheapest bid. They just hang their heads say we should have went with you!!!!!! payup
  10. plantace

    plantace LawnSite Member
    Posts: 6

    No, actually it's granite dust, or some sort of schist or basalt. Those are primarily our native bedrock types, and we have no limestone outcroppings. Thus, decomposition isn't a problem, except on a geologic time frame.

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