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Is a foundation slab REALLY necessary - Forno Bravo Forum: The Wood-Fired Oven Community

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Is a foundation slab REALLY necessary

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  • Is a foundation slab REALLY necessary

    IS building a foundation slab REALLY necessary if you already have a concrete patio set up in the backyard?

    I mean.. the foundation is already built there and my grills reside there on the spot... so cant I just skip on by this step and get to building the stand next?

    It would be much more time and cost-efficient.

    So... is this okay in anyone's opinion?

  • #2
    Re: Is a foundation slab REALLY necessary

    It all depends on the patio. If it's at least three and a half inches thick (which you can tell) and reinforced (which you can't) and properly drained (which is important to avoid frost heave), you're good to go. Remember, your oven is VERY heavy, your grill is a feather compared to it. If the weight of the oven cracks or shifts your patio there's no going back short of reconstructing it.

    That said, i'd be tempted to use the existing pad. One builder diamond cut a section of an existing patio, so that if it cracked it wouldn't wreck the whole patio.
    My geodesic oven project: part 1, part 2

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    • #3
      Re: Is a foundation slab REALLY necessary

      The heaviest part of a WFO, if you build it the way Forno Bravo recommend in their Pompeii Oven Instructions, is the support stand and slab. All that heavy blockwork, rebar and poured concrete is enough to support the Empire State Building! The oven itself is just a few bricks cut in half with some lightweight Vermiculite or Perlite insulation and doesn't need all that over-engineering. It's even lighter if you use all Insulite blanket insulation.

      Whether your patio paving will hold the weight depends on how the slabs have been laid. If they've been cemented down then you should have no problem. Laid on loose sand or similar then you will need a firmer foundation.

      If they're firmly laid then build your blockwork with 4" concrete blocks instead of the monsters recommended. Build them as you would a brick wall. Use 2inch thick paving slabs for the top of the stand on which you'll build your hearth and cooking floor as recommended in the instruction. I used this method on an existing patio without any problems. It even withstood a minor earthquake!

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      • #4
        Re: Is a foundation slab REALLY necessary

        Originally posted by achilles007 View Post
        IS building a foundation slab REALLY necessary if you already have a concrete patio set up in the backyard?

        I mean.. the foundation is already built there and my grills reside there on the spot... so cant I just skip on by this step and get to building the stand next?

        It would be much more time and cost-efficient.

        So... is this okay in anyone's opinion?

        I built mine on an existing 3.5 inch slab.
        I do have one long crack... but my slab was also cracked where I placed the oven. And I think there was some more settling.
        BUT I did rush the curing process, so I really don't know what caused the crack.

        I'm still cooking though... 2 years later....I never notice the crack anymore.
        But, who cares, the crack adds character and the cooking is superb...whether you are making pizza or BBQ or turkeys or steak or chicken...

        so I say yes.


        Enjoy your build.

        BTW - asudavew=redneck.

        (if i was starting from scratch... 5.5 inch slab, but existing 3.5 who cares! go fer it)
        My thread:
        http://www.fornobravo.com/forum/f8/d...ress-2476.html
        My costs:
        http://spreadsheets.google.com/pub?k...Xr0fvgxuh4s7Hw
        My pics:
        http://picasaweb.google.com/dawatsonator

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        • #5
          Re: Is a foundation slab REALLY necessary

          Originally posted by dmun View Post
          It all depends on the patio. If it's at least three and a half inches thick (which you can tell) and reinforced (which you can't) and properly drained (which is important to avoid frost heave), you're good to go. Remember, your oven is VERY heavy, your grill is a feather compared to it. If the weight of the oven cracks or shifts your patio there's no going back short of reconstructing it.

          That said, i'd be tempted to use the existing pad. One builder diamond cut a section of an existing patio, so that if it cracked it wouldn't wreck the whole patio.
          Originally posted by Nev Grady View Post
          The heaviest part of a WFO, if you build it the way Forno Bravo recommend in their Pompeii Oven Instructions, is the support stand and slab. All that heavy blockwork, rebar and poured concrete is enough to support the Empire State Building! The oven itself is just a few bricks cut in half with some lightweight Vermiculite or Perlite insulation and doesn't need all that over-engineering. It's even lighter if you use all Insulite blanket insulation.

          Whether your patio paving will hold the weight depends on how the slabs have been laid. If they've been cemented down then you should have no problem. Laid on loose sand or similar then you will need a firmer foundation.

          If they're firmly laid then build your blockwork with 4" concrete blocks instead of the monsters recommended. Build them as you would a brick wall. Use 2inch thick paving slabs for the top of the stand on which you'll build your hearth and cooking floor as recommended in the instruction. I used this method on an existing patio without any problems. It even withstood a minor earthquake!
          Originally posted by asudavew View Post
          I built mine on an existing 3.5 inch slab.
          I do have one long crack... but my slab was also cracked where I placed the oven. And I think there was some more settling.
          BUT I did rush the curing process, so I really don't know what caused the crack.

          I'm still cooking though... 2 years later....I never notice the crack anymore.
          But, who cares, the crack adds character and the cooking is superb...whether you are making pizza or BBQ or turkeys or steak or chicken...

          so I say yes.


          Enjoy your build.

          BTW - asudavew=redneck.

          (if i was starting from scratch... 5.5 inch slab, but existing 3.5 who cares! go fer it)
          GREAT information guys!

          Thank you so much.. so I will have to get some information on this patio then. be right back with the updates. thanks a ton, guys

          Comment


          • #6
            Re: Is a foundation slab REALLY necessary

            I may be the lone dissenter here but I don't think there is a single answer to this question. It depends on where you live and what kind of base the slab sits atop.

            Speaking only for myself, the aggravation if something did go wrong like a crack or shift in the slab that caused a crack or fracture on the oven dome outweighs any savings in time or money.

            Comment


            • #7
              Re: Is a foundation slab REALLY necessary

              I'm with DimTex on this one.

              Building on a slab is OK, but only if you are fairly sure about the condition of the slab. Also the slab supporting the oven should be isolated from the rest of the patio.

              I would do further investigation of the existing slab. (Talk to the previous owner / builder ?). If in doubt I might do something like saw cut it to isolate it from the rest of the patio and form and pour a 3 1/2 inch reinforced new slab on top.
              Last edited by Neil2; 07-08-2009, 02:51 PM.

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