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A few questions about hearth insulation and mass - 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.

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A few questions about hearth insulation and mass

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  • A few questions about hearth insulation and mass

    Hello all!

    I am beginning to build a 36" pompeii. I already have the base poured and am ready for the hearth insulation.

    Question 1: Does 4" of vermiculite concrete have about as much insulation value as 2" of FB board or SuperIsol?

    Question 2: I have some firebrick splits around from a maple syrup evaporator I no longer use and am wondering about putting a layer of them under the the regular size hearth brick for some added mass. We are big bread fans in addition to pizza lovers and I thought a little more mass might be nice for baking bread. And it seems to me like having close to the same amount of mass on the hearth as there is on the dome would make sense. Am I right or wrong? Also......could anyone give me an idea of how much longer it would take to heat the oven with this added mass?

    This is a great forum and I am so glad I found it before I started on a Allan Scott oven which would've had way too much mass for me!

    Thanks

  • #2
    Re: A few questions about hearth insulation and mass

    OK....I decided to use calcium silicate boards for insulating the hearth. But, I'm still wondering about adding mass under the hearth. Especially in relation to baking bread. Does anyone have any advice or other input to give me about it?

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    • #3
      Re: A few questions about hearth insulation and mass

      If you want more mass, you can turn the firebrick on their sides for the floor, giving you 4.5" of mass, but unless you plan on multiple batches, you will spend more time firing than it is worth.

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      • #4
        Re: A few questions about hearth insulation and mass

        Hi Geek,

        Ask this question in the Pompeli Oven Construction tab. It is much more active. But to answer your question, at least from my perspective. I have 2" of FoamGlass topped with 1 1/2" of CaSi with a 3" thick high density fire brick floor. The HD bricks and increased thickness seems take longer to saturate but once charged they also seem to hold the floor heat. I would think 2" of CaSi is your min. There is no significant insulation gained by the splits but does add mass consider more CaSi or a V-crete layer under CaSi. My two cents.
        Russell
        Build Link............... Picassa Photo Album Link

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        • #5
          Re: A few questions about hearth insulation and mass

          Originally posted by Tscarborough View Post
          If you want more mass, you can turn the firebrick on their sides for the floor, giving you 4.5" of mass, but unless you plan on multiple batches, you will spend more time firing than it is worth.
          Thanks so much for your input. I thought about using bricks on the side but I already have the splits and so it would be more cost effective to use them instead.
          The way I perceive we will be using the oven is this: Starting with pizza then after that one or two batches of bread then possibly on occasion some smaller pastries. would the standard 2.5" hearth handle that fine?

          Originally posted by UtahBeehiver View Post
          Hi Geek,

          Ask this question in the Pompeli Oven Construction tab. It is much more active. But to answer your question, at least from my perspective. I have 2" of FoamGlass topped with 1 1/2" of CaSi with a 3" thick high density fire brick floor. The HD bricks and increased thickness seems take longer to saturate but once charged they also seem to hold the floor heat. I would think 2" of CaSi is your min. There is no significant insulation gained by the splits but does add mass consider more CaSi or a V-crete layer under CaSi. My two cents.
          Thanks for the tip about the thread location! I really should start a proper build thread with pics so I can just ask questions there. I will have enough CaSi board for more than 2" so I think I'll be fine there.

          I'm still wondering if more floor heat is better for bread or doesn't it really make that much of a difference?

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          • #6
            Re: A few questions about hearth insulation and mass

            Standard hearth will easily handle what you're describing. When people talk about "multiple batches" of bread, they usually mean production-level quantities, not the 10kgs (20 one pound loaves) you're going to bake in two batches.

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            • #7
              Re: A few questions about hearth insulation and mass

              Originally posted by azatty View Post
              Standard hearth will easily handle what you're describing. When people talk about "multiple batches" of bread, they usually mean production-level quantities, not the 10kgs (20 one pound loaves) you're going to bake in two batches.
              Awesome! Thanks!

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              • #8
                Re: A few questions about hearth insulation and mass

                Adding mass under the floor as you suggest will result in slower heat up of your oven floor and negate the usefullness of your insulation to a point. Think of it this way. The added mass will heat up only by drawing the heat away from your floor. The insulation under your "mass" will allow for longer heat retention but will do nothing to aid in the heating of your floor. As for baking breads (I too am a fan) I don't think that the added mass that you are talking about will be that benifitial, but of course I don't know what your plans are. Just saying that I have been able to use my oven to bake bread after I was done with making pizzas.

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