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Vermiculite questions - Forno Bravo Forum: The Wood-Fired Oven Community

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Vermiculite questions

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  • Vermiculite questions

    Apologies if I'm asking questions that have already been answered but I'm unsure about a few points for my hearth insulation. From what ive read it appears that 5:1 or 6:1 by volume is an appropriate vermiculite:concrete mix. I've read comments that I shouldn't use a mixer to do this but I've also read instructions suggesting its ok to use a mixer.
    Also, I think I need to mix dry ingredients then add water, is this correct?
    How much should I tamp or pack it, and how wet should it be?
    Should I simply dump it in and screed the top to level?

    Thanks

    R

  • #2
    Re: Vermiculite questions

    Originally posted by RichC View Post
    Apologies if I'm asking questions that have already been answered but I'm unsure about a few points for my hearth insulation. From what ive read it appears that 5:1 or 6:1 by volume is an appropriate vermiculite:concrete mix. I've read comments that I shouldn't use a mixer to do this but I've also read instructions suggesting its ok to use a mixer.
    Also, I think I need to mix dry ingredients then add water, is this correct?
    How much should I tamp or pack it, and how wet should it be?
    Should I simply dump it in and screed the top to level?

    Thanks

    R
    By all means use a mixer if you wish. I don't because I've found that it tends to stick to the sides of the mixer too much. Also the grains will break down somewhat in a mixer, whereas mixing gently in a barrow less so. Every batch of vermiculite is a bit different and depending on humidity or if the stuff has got wet, but I find for every 10 parts vermiculite you need 3 parts water. If you end up with water pooling in the bottom of the mix then you've added too much.i mix the cement and vermiculite dry first then add the water.the mix will seem too loose and dry so yes tamp it a little, but you don't want to compress it too much or you will lose insulation value.
    Kindled with zeal and fired with passion.

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    • #3
      Re: Vermiculite questions

      Thanks Dave

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      • #4
        Re: Vermiculite questions

        Made my first batch of vermicrete today. Not sure at all about the consistency. Made a slurry of about 13litres water to 1/2 bag(12.5kg) cement then mixed this into a 50litre bag of vermiculite in my wheelbarrow. It was very hard to reduce the amount if small balls. The mix also seemed very dry(although these quantities were recommended by the supplier). It's about a 6:1 mix. It was a bit like damp sand when mixed only lighter. Can someone tell me if this is right?
        Thanks

        R

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        • #5
          Re: Vermiculite questions

          sounds about right to me. Let it dry and check the firmness then. mine was like an old dried up sponge kinda when set. it had some give to finger pressure, but had to press hard. very technical answer, i know. It is strange stuff to work with i remember and i thought at the time this cant be right, but it all is fine once set.

          Texman
          My Progress:
          http://www.fornobravo.com/forum/f8/t...ild-17324.html

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          • #6
            Re: Vermiculite questions

            Thanks Tex, I just needed to hear it from someone who's done it before

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            • #7
              Re: Vermiculite questions

              Originally posted by RichC View Post
              Made my first batch of vermicrete today. Not sure at all about the consistency. Made a slurry of about 13litres water to 1/2 bag(12.5kg) cement then mixed this into a 50litre bag of vermiculite in my wheelbarrow. It was very hard to reduce the amount if small balls. The mix also seemed very dry(although these quantities were recommended by the supplier). It's about a 6:1 mix. It was a bit like damp sand when mixed only lighter. Can someone tell me if this is right?
              Thanks

              R
              Sounds like it will work. I like to use 3 parts water for every 10 of vermiculite, which would put yours at just over 16 litres rather than the 13 you used. After 24 hrs you should find it has gone harder. Allow it to dry, but keep rain off it, for a couple of weeks before covering it over with brick. See attach doc on drying vermicrete.
              Attached Files
              Kindled with zeal and fired with passion.

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              • #8
                Re: Vermiculite questions

                Thanks guys, finished my under heart vermicrete layer. Mixed at about 6:1 and was quite dry using the manufacturers recommendations. About 135mm gone in. I assume it'll have to be much wetter for the dome insulation as the consistency I was working with would never enable me to build up the sides of the dome. Do you guys find you need a much wetter mix for covering the dome?

                Thanks

                Richard

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                • #9
                  Re: Vermiculite questions

                  I use the same amount of water, but 10:1 vermicrete,cement over the dome. If you add too much water it will pool in the bottom of your barrow and tend to wash the cement off the grains.Apply it in small handfuls, pressing and holding for a couple of seconds. Starting from the bottom of the dome, leaving a little ledge on the top to take the next row.
                  Kindled with zeal and fired with passion.

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