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Yet another insulation question - Forno Bravo Forum: The Wood-Fired Oven Community



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Yet another insulation question

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  • Yet another insulation question

    Last edited by wotavidone; 03-31-2013, 12:25 AM.

  • #2
    Re: Yet another insulation question

    They're both the same. Same insulating properties, same manufacturing processes (they are expanded minerals - popped in heat like popcorn).

    Perlite is white: it makes a good visual marker when your gray portland is evenly distributed.

    Vermiculite is said to be less dusty.

    Neither one of these is a deal killer in my book.
    My geodesic oven project: part 1, part 2


    • #3
      Re: Yet another insulation question

      I used half perlite and half vermiculite. I found this a bit easier to work with that straight vermiculite, particularly when forming/screeding the dome layer.


      • #4
        Re: Yet another insulation question

        Originally posted by dmun View Post
        They're both the same. Same insulating properties, same manufacturing processes
        Hi dmun,

        Do Perlite and Vermiculite actually have the same insulating properties?

        Forgive the question, I'm just a natural-born-fool from Gippsland, but the data I have indicates that Perlite has a thermal conductivity almost half that of Vermiculite (0.031W/m.K for Perlite, 0.058W/m.K for Vermiculite).
        The Melbourne Fire Brick Company


        • #5
          Re: Yet another insulation question

          I suspect there are a lot of variables involved with Perlite/Vermiculite/Portland insulation value. Grain size, ratio of Portland, how long it's mixed, etc.

          For our purposes (insulating under an oven floor), 4" of either material will give you satisfactory results. Is one better than another in a laboratory? Probably. Are you going to notice a difference in your oven. I seriously doubt it.

          It's like comparing flat panel TV's at Walmart. One might look a little better in the store, but either will look great in your living room.
          Ken H. - Kentucky
          42" Pompeii

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          • #6
            Re: Yet another insulation question

            Thank you Ken for that analysis. For our needs, there is no reason to re-invent the wheel.
            knowledge is contagious, spread the infection!!!


            • #7
              Re: Yet another insulation question

              Last time I checked thermal conductivity it said perlite was just a slightly better insulator than vermiculite, not double. I prefer to use vermiculite because it seems to mix up better and hasn't got that irritating dust that perlite seems to have. The perlite I use tends to abrade more than the vermiculite on mixing and you end up losing a bit of volume. You are not meant to mix either of them for too long, i think for this reason. Vermiculite also seems to coat with the cement a bit better, the grains of perlite are rounder and smoother and it doesn't seem to stick as well. Sorry for the extended answer. If I were making a choice between the two I'd take vermiculite.
              Last edited by david s; 06-26-2011, 01:29 PM.
              Kindled with zeal and fired with passion.


              • #8
                Re: Yet another insulation question

                For under floor insulation, you cant beat calcium aluminate board, end of story.
                OOPs that should be Cal. Silicate board.
                Last edited by Johnny the oven man; 06-26-2011, 09:27 PM.


                • #9
                  Re: Yet another insulation question

                  Thanks for your response Ken and David, and don't worry, I like extended answers!
                  The Melbourne Fire Brick Company