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Thread: Concrete Patio

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  1. #1
    Join Date
    Jan 2010
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    Question Concrete Patio

    I am getting ready to do a concrete Patio off our dinning room. Our property sits on Clay soil. I have heard and seen how the clay can damage concrete if it is not done properly. I would like to see if anyone knows how to prep the soil and ground so the concrete will last. the patio is going to be 20 X 20 so 400 Sq feet. I dont know if I need to be s certain thickness or what. If anyone has any ideas please share them...Thanks Hans

  2. #2
    Join Date
    Mar 2009
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    Default Re: Concrete Patio

    Howdy, depending on how expansive the clay is will affect the slabs movement. To help consider adding cement wire mesh or even better 1/2" re bar in a lattice pattern 1.5 inches into the cement above the soil. Might also add fiberglass fiber to the mix but the fibers are visible in finished work. Makes sure the slop is away from the slab. Be sure to have no down spouts draining adjacent to the slab. Consider a felt saturated with tar expansion joint against the house foundation and strike the pad every 20 sq foot to control cracking..

  3. #3
    Join Date
    Aug 2007
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    Default Re: Concrete Patio

    Quote Originally Posted by Timothy Miller View Post
    Consider a felt saturated with tar expansion joint against the house foundation and strike the pad every 20 sq foot to control cracking..
    As Tim notes, fiberglass fiber will be visible in the finished concrete, not something I'd recommend for a patio, go with rebar or mesh.

    I personally don't like the look of visible expansion joints. Wood joints will rot out over time, the felt won't, but it's a big ugly black thing that sticks out like a sore thumb. IMHO, a felt expansion joint is only necessary when the concrete will be in a confined space, even then it's questionable in most situations. Trex would be a suitable alternative that won't rot an still looks somewhat wood-like.

    Striking every 20sqft is a little overkill, one strike line at the center point in both directions will suffice. Use a 1" seaming tool for the job and you'll have no issues. Another alternative would be to pour four individual pads. It's a little more work and draws out the pour time a little, but in the end it's easier because you're doing less concrete at a time and you do not have to seam or use expansion joints because this method of pouring automatically puts those joints in and they will be virtually invisible.

    Minimum slab thickness should be 3-1/2". Make sure that it slopes away from the house by a minimum 1/8" per foot and a maximum 1/4" per foot. The surface should be at least 1/2" below the bottom of the door threshold.
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  4. #4
    Join Date
    Aug 2007
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    The Great White North
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    Default Re: Concrete Patio

    To add to Sprucey's post ---- there isn't a mention of what area you're in ------ If there will be frost heave or not.

    Preperation is a main factor to the longevity to the pad.

    A proper sub-base is critical ---- especially with clay soil and / or ground frost.

    It's a good idea to excavate away any top soil along with any other organics like roots and get down to good layer of clay .

    Place a geo-texitle ( heay land scape fabric ) down on top of the clay to seperate 6 - 12 inches of 3/4 down stone base , from the soil ---- don't use plastic the fabric allows ground water to pass through.

    Rent a vibrating compactor and run it over the 3/4 down stone.

    Lay the rebar or mesh and pour the concrete.
    "" an ounce of perception -- a pound of obscure "
    - Rush

  5. #5
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    Aug 2007
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    Default Re: Concrete Patio

    Quote Originally Posted by canuk View Post
    To add to Sprucey's post ---- there isn't a mention of what area you're in ------ If there will be frost heave or not.
    I always forget about that tidbit for those that like to live in the white stuff. In cases like this I recommend moving to warmer climates ...

    Quote Originally Posted by canuk View Post
    Preperation is a main factor to the longevity to the pad.

    A proper sub-base is critical ---- especially with clay soil and / or ground frost.
    True, no matter where you live. Even here I've seen slabs that were 0" to over 12" thick because there was no prep done. You can guess why the slabs had to be replaced. No, I'm not exaggerating with the 0". I've seen more than one hole form over a dirt clod that only had a layer of cream skimmed over the top of it.
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  6. #6
    Join Date
    Mar 2009
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    Default Re: Concrete Patio

    Howdy, the use of an asphalt impregnated expansion joint against the house to isolate the patio slab so if clay soils expand the slab will move up without possibly buckling and breaking next to the foundation of the home - for $10.00 in material great piece of mind. The every 20 square foot to strick a expansion joint is recommended by soil engineers for clay soils.I would have the slab cut with a cement saw after poured so the expansion joints are pretty straight lines, looks great, acts great, and allot less chance of any cracking where you do not want it.

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