Patio on clay

Discussion in 'Landscape Architecture and Design' started by site, Apr 23, 2001.

  1. site

    site LawnSite Member
    Messages: 168

    I saw some threads last year about adding lime to clay to stiffen it up in order to build a patio above. How much lime do you use? Do you till it in and then run the compactor over it? Anything else I should know?
    In the past we have just dug down extra deep and replaced clay with gravel. It seems like where people have clay it is bottomless-several feet or more deep, and we still have shifting problems sometimes when we use our current method.
  2. WALT

    WALT LawnSite Member
    Messages: 27

    Adding lime to the clay will acctually suck up the water by a chemical reaction. The chemical being calcium oxide, which reacts with water, giving off heat and expanding into calcium hydroxide. This will make the soil from a moldable - soupy mass to a crumbly soild.
    As far as how much, depends on how moist or wet it is. Lime is fairly inexpensive, so go to town. It is messy and definatley use a dust mask.
    Work it into the soil with a tiller 4-8" deep. Then wait, overnite perferably, to see results, add more if needed the same way. Run the tamper over it a few times, but not extra long because this will brig what moisture that's still underneath up to the top.
    You should have a good subbase for a patio. Add base course, crush rock, to it to finish it off.
    Digging down extra deep, of course would be an excellent way indeed. Depends on what you can or cannot charge the customer is what I would base it on.
    Hope this helps...
  3. Guido

    Guido LawnSite Silver Member
    Messages: 2,087

    Your Bible must be close by! ;)

    You beat me to it!
  4. neighborguy

    neighborguy LawnSite Member
    Messages: 186

    Southeastern WIsconsin is notoriously filled with clay. When we dig our patios we dig to a depth of 10-12". This leaves 7 1/2" to 9 1/2" for our 3/4" to dust crushed limestone. I have never heard of actually rototilling in lime to bring out moisture. The only thing I can think of is that we don't add the lime because we are using crushed limestone which may have the same effect(?)
  5. Stonehenge

    Stonehenge LawnSite Bronze Member
    from Midwest
    Messages: 1,276

    Neighborguy - sounds like you know a bit more about pavers than you let on in your other thread on pricing. However, 10-12"? That's pretty deep. AASHTO says 4-6" base is plenty for the kind of ESALs a patio or walk would receive in our neck of the woods.
  6. WALT

    WALT LawnSite Member
    Messages: 27

    Lime is obtained by cooking limestone at high temputures, so it then becomes calcium oxide, which WILL react with water, giving off heat.
    I myself have done this, and seen it work. I have also read it in a number of articles and books.
    If crushed limestone has the same affect, I don't know. I can imagine it's a fine base course, but I haven't had the pleasure of using it.
    Curious as to what you do if a depth of 10-14" the sub-base is still "pumping" from the dampness?
  7. neighborguy

    neighborguy LawnSite Member
    Messages: 186

    sorry it took so long to reply, been busy (I know; preaching to the choir).

    Stone- I guess that we have always gone that deep to cover our rears. I haven't had any problems selling a client on the possible benefit of a thicker base to resist the freeze/thaw cycle a little longer than a thinner base. If I start to lose jobs over the base depth, I will probably have to change my routine.

    Site- I have yet to run into a situation where my subbase was really wet at our final depth.

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