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Vermicilite /Cement ratio - Forno Bravo Forum: The Wood-Fired Oven Community


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Vermicilite /Cement ratio

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  • Vermicilite /Cement ratio

    I am mixing my cement with 3 to 1 cement gravel mix to Portland cement. How much Vermiculite should I add to this mix to optimize the insulating value of the Hearth?

  • #2
    Insulating concrete

    Ciao Fudugazi,

    The insulating concrete is 5-6 parts of vermiculite to 1 part portland cement. The vermiculite is the only aggregate, so in that sense, you are not adding vermiculite to redi-mix concrete (where sand and gravel are the aggregate).

    Any easy way of doing this is to mix the vermiculite and portland together (where the portland coats the vermiculite) when they are dry, then you add water until you get an oatmeal texture. I have heard that mechanical mixers can beat up the vermiculite and ruin the hole structure.

    The mixture is light, and easy to work with. It's also cheap and efficient.
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    • #3


      Just a back up here. Six to one is the ratio I'd use, and no ready mix. A mechanical mixer will beat up the vermic way too much. Mix it dry, then add water. The resulting wet mix is light and easy to work with, the lightest in the entire project.

      "Made are tools, and born are hands"--William Blake, 1757-1827


      • #4

        Thanks guys Got it The mixture gets poured this weekend on Lake of The Woods!!!! Ciao Fudugazi


        • #5
          Re: Vermicilite /Cement ratio

          hi guys , i'm mixing my vermiculite base this weekend, do i use "ordinary" cement for the mix or do i need to use heat proof cement ??? cheers for any feedback ...Dave..


          • #6
            Re: Vermicilite /Cement ratio

            Ordinary cement..

            Big tip, soak the vermiculite first.. worked a treat when i did mine..

            And i just added cement till it felt right, think it ended up around 4-1 or 5-1


            • #7
              Re: Vermicilite /Cement ratio

              As Canuck Jim says, mix it gently by hand. You don't want to break up the vermiculite particles thus increasing the density and reducing the insulating value.

              I suggest a 6:1 mix under the hearth and a 12:1 mix for over the dome.
              Last edited by Neil2; 06-07-2011, 07:03 PM.


              • #8
                Re: Vermicilite /Cement ratio

                Careful you don't add too much water or it will wash the cement off the vermiculite and sit in the bottom of your barrow/container. I've found 10:3.5 by volume of vermiculite, water works well and for the really fine stuff go to 10:4
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