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hearth floor construction - Forno Bravo Forum: The Wood-Fired Oven Community

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I'm Peter Reinhart! Ask Me Anything! Monday, February 15, 2016 7:00-8:00 pm EST

To kick off our AMA feature, we have invited author, chef and master bread maker and host of Pizza Quest, Peter Reinhart, to be our first host! Peter will be in the Forum on Monday, February 15th, from 7:00 - 8:00 pm EST. If you are unable to be online during the live session, you can post your questions in the sticky post. Peter will answer those questions during the live session on February 15th. You can view Peter's answers to your questions as well as what happened during the live session in the session thread.

Ask Me Anything New Forum Feature

You will notice a new forum at the top of the main page called, "Ask Me Anything". This forum will be used for live one hour "Ask Me Anything" (AMA) sessions hosted by people who are knowledgeable in different areas pertaining to wood fired ovens. How it works:
- Each AMA will have a "sticky" thread where the community can post questions they would like answered during the live session. This will allow everyone to participate even if you can't be online for the live session. These questions will not be answered by the host until the live AMA; if you need an answer quickly, you should post it in the appropriate Forum area for the community to respond.
- Another thread will be posted for the live AMA. Registered users who are logged in during the live session can interact with the host by asking questions and receiving responses.
- The live thread will remain in the AMA forum to view after the session.

We hope you enjoy this new feature! Please let us know if there is a topic that you'd like to have as an AMA and we'll look for a host!

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  • hearth floor construction

    I am building a 36" dome oven. The base is ~50"x70" for the hearth floor with 2" angle iron on 16" center. I intend to use 1/2" concrete board and then a mixture of portland cement, quickcrete concrete, vermiculite with rebar and make that layer ~2" and set my 24x12x3 firebrick slabs on that.

    Question is do you think the mixture of concrete, cement and vermiculite is OK?

  • #2
    Re: hearth floor construction

    Welcome to the forum.

    In my mind, you need a structural base (my hearth base was 3.5 inches thick with angle iron and rebar), then an insulating layer (I used a two inch insulating board), then the oven floor (2.5 inch firebrick). I recommend you download and read the pompeii oven plans, they lay out the process for a strong base/hearth structure and a proven oven. Quickcrete will suffice for the hearth, but I would not mix the vermiculite in the structural base. Cast the vermicrete layer over the structural base/hearth. HTH
    Lee B.
    DFW area, Texas, USA

    If you are thinking about building a brick oven, my advice is Here.
    Our One Meter Pompeii Oven album is here.
    An album showing our Thermal Breaks is Here.

    I try to learn from my mistakes, and from yours when you give me a heads up.

    Comment


    • #3
      Re: hearth floor construction

      I agree with Lee. What you describe will not insulate well and you will likely have difficulty getting the floor temperature up to where you want it. I used 3 inches of insulating board over a concrete base and I am very happy with the results!

      Comment


      • #4
        Re: hearth floor construction

        Originally posted by avkroth View Post
        .....and then a mixture of portland cement, quickcrete concrete.............
        There is no need to add Portland cement to a bagged concrete product.
        Old World Stone & Garden

        Current WFO build - Dry Stone Base & Gothic Vault

        When we build, let us think that we build for ever.
        John Ruskin

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        • #5
          Re: hearth floor construction

          That depends Stonecutter. A lot of what is sold in big box stores is only rated at 2500 PSI, with actual breaks well below that. If it is their lowest cost product, a shovel per 80# bag is a good thing.

          Comment


          • #6
            Re: hearth floor construction

            Yeah, I agree, but for an oven slab its overkill.
            Old World Stone & Garden

            Current WFO build - Dry Stone Base & Gothic Vault

            When we build, let us think that we build for ever.
            John Ruskin

            Comment


            • #7
              Re: hearth floor construction

              For the slab, yeah, but I thought he was talking about the hearth.

              Comment


              • #8
                Re: hearth floor construction

                Yes that's right, but I saw he is installing angle at 16" oc for the hearth slab. So 2500 is plenty strong with that kind of support. It's possible that his bag mix is the 5000 psi stuff....and more porty is way overkill that too.
                Old World Stone & Garden

                Current WFO build - Dry Stone Base & Gothic Vault

                When we build, let us think that we build for ever.
                John Ruskin

                Comment


                • #9
                  Re: hearth floor construction

                  I should just say I agree that a shovel of porty is good insurance for a #80 bag...and cheap. It is possible to add too much Portland in a mix design, but I think I am over thinking this.
                  Old World Stone & Garden

                  Current WFO build - Dry Stone Base & Gothic Vault

                  When we build, let us think that we build for ever.
                  John Ruskin

                  Comment


                  • #10
                    Re: hearth floor construction

                    just gotta ask....to clear my own mind...what happens if there is too much portland in a mix?
                    jon

                    Comment


                    • #11
                      Re: hearth floor construction

                      Brittle concrete
                      Old World Stone & Garden

                      Current WFO build - Dry Stone Base & Gothic Vault

                      When we build, let us think that we build for ever.
                      John Ruskin

                      Comment


                      • #12
                        Re: hearth floor construction

                        Shrinkage cracking primarily, but ultimately if it is out of proportion it will weaken the mix design in flexural strength.

                        For the foundation slab, almost anything is strong enough, even the "fence-crete" garbage the big box stores sell as is. For anything with a span or cantilever you need more flexural strength which is tied to compressive, and the thinner the more important it is. If you are pouring a full 4" slab for the hearth, then a 2500 PSI is adequate. If you are slimming it down to 2-3" it is safer to use something with a higher flexural strength.

                        Flexural strength is not a standard that is used to designate bag mixes though, so you will never see it listed, and must infer it from the compressive.

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                        • #13
                          Re: hearth floor construction

                          what role does the rebar play into the flexural strength of concrete?
                          jon

                          Comment


                          • #14
                            Re: hearth floor construction

                            Almost all of it, provided it is placed correctly.

                            Comment


                            • #15
                              Re: hearth floor construction

                              so if two layers of bar are used, the top mat is under compression and the bottom mat would be under stress?
                              jon

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