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What is Vermiculite - Forno Bravo Forum: The Wood-Fired Oven Community



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What is Vermiculite

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  • What is Vermiculite

    I found this on the Internet, and thought it was interesting. It is a type of heat-resistant, insulating, volcanic popcorn. As a side note, the vermiculite we get at Home Depot in California has a "certified asbestos free" label.



    Vermiculite has been used in various industries for over 80 years. It is used in the construction, agricultural, horticultural, and industrial markets.

    Vermiculite is the mineralogical name given to hydrated laminar magnesium-aluminum-ironsilicate which resembles mica in appearance.

    Vermiculite is found in various parts of the world. Locations of the predominant commercial mines are in Australia, Brazil, China, Kenya, South Africa, USA and Zimbabwe.

    Vermiculite mines are surface operations where ore is separated from other minerals, and then screened or classified into several basic particle sizes.

    When subjected to heat vermiculite has the unusual property of exfoliating or expanding into worm-like pieces (the name vermiculite is derived from the Latin 'vermiculare' - to breed worms).

    This characteristic of exfoliation, the basis for commercial use of the mineral, is the result of the mechanical separation of the layers by the rapid conversion of contained water to steam.

    The increase in bulk volume of commercial grades is 8 to 12 times, but individual flakes may exfoliate as many as 30 times. There is a color change during expansion that is dependent upon the composition of the vermiculite and furnace temperature.

    The bulk density of crude vermiculite or vermiculite concentrate is in the range of 640-1120 kg/m³ (40-70 lb/ft³) and exfoliated or expanded vermiculite is in the range of 64-160 kg/m³ (4-10 lb/ft³).
    Last edited by james; 10-16-2007, 10:29 AM.
    Pizza Ovens
    Outdoor Fireplaces

  • #2
    Asbestos Free - off topic

    That is due to California Proposition 65 which states that living may be dangerous to your health. For those not familiar with the Kalifornia law it states that businesses must post signs telling consumers what products may be found in the business that could cause cancer/ birth or developmental defects. Numerous frivolous lawsuits have resulted since its inception in 1986. Scuba shops in the LA area were hit with a lawsuits for not having signs out warning about lead. That is what is used to counter balance the air in you tanks, the fat on your body and the wet or dry suit you are wearing of course depleted uranium and gold would be heavier but they are a bit more dear $$. You would think that common sense would tell you to not eat lead and wash you hands after playing with lead but I have been told that common sense is not common. So if a business plans on staying in business then just about every business will have a blanket statement stating that the establishment contains chemicals that are on the Prop 65 list.

    As for Asbestos Free – vermiculite may contain asbestos a natural occurring mineral. You can process the fines to remove the vermiculite from the asbestos. When in doubt wear a respirator mask. Just because it is asbestos free doesn’t mean that the vermiculite will not cause lung damage if you inhale it.

    It is best to wear a mask any time you are working around products that put dust into the air, be it coal, fiberglass, insulation, plaster, or cutting brick.

    licensed Professional Mechanical Engineer


    • #3
      It's free

      Hi Patrick,

      I'm not sure that's exactly right. Prop. 65 says that you have to make a label when something known to be harmful is present (one of my favorites is the "lead" in lead chrystal -- make sure you don't make drinking water pipes out of your candle stick). In this case, I think they are making the point that the harmful compound (Asbestos in this case) ins't there. I took another look today, and it says "certified Asbestos free".

      Completely off topic, our dog had a pill for "verme" in modern Italian -- or worms. I guess Vermiculite does look like worms.

      Pizza Ovens
      Outdoor Fireplaces


      • #4

        Just a quick note on asbestos in vermiculite. The material itself is a kind of expanded shale, and it comes in very fine granules (Pool Pac) and much larger pieces, both used for insulation. In the larger form, it looks a bit like mica. If there is asbestos present, I suspect it would be in miniscule (ppm) amounts. I used 11 bags of Pool Pac in my Alan Scott oven.

        On safety: at one stage in my early career, I worked in a silver mine in the Yukon Territory, and I probably was more exposed to lead, zinc, etc.,etc. than any 50 people I know, and I'm still here.

        In general: I'm really pleased and thankful that this group exists, and I could join it. My oven is almost ready to bake, and I've got tons of questions, including large batch recipes. In the past, I've only baked in small amounts.
        "Made are tools, and born are hands"--William Blake, 1757-1827


        • #5
          Hey Jim,

          Welcome aboard. I am looking forward to hearing more on your bread baking. I'm a hobbyist baker and would enjoy seeing more threads on bread. Mixers, techniques, flour, whole grains, pans, proofing, oven temperature, et al.

          Let's see if we can get an active group in the Bread section of the forum.

          Pizza Ovens
          Outdoor Fireplaces


          • #6
            If you can’t get your hands on Vermiculite Perlite is a good alternative. Try and get the largest granule size you can, as it is easer to apply to the oven dome. On a recent oven installation in Athens we could only get hold of Perlite with a granule size of 5-10 mm, the concrete was rather difficult to work with at first but the end result was ok.

            For more info on Vermiculite or Perlite try http://www.vermiculite.org/ and http://www.perlite.org/



            • #7
              Re: What is Vermiculite

              I have sourced Vermiculite from a Garden Center at $28 per 4 CU FT bag and a building supply center at $14.00 per 4 CU FT Bag. The building supply centre assured me it was asbestos free. He says is General Purpose. Can I go with either or do I need to be concerned that the building supply stuff could be treated with something that makes it un-useable? I read somewhere that silicone may sometimes be used?

              Check out my build at:


              • #8
                Re: What is Vermiculite

                Originally posted by tdibratt View Post
                I have sourced Vermiculite from a Garden Center at $28 per 4 CU FT bag and a building supply center at $14.00 per 4 CU FT Bag. The building supply centre assured me it was asbestos free. He says is General Purpose. Can I go with either or do I need to be concerned that the building supply stuff could be treated with something that makes it un-useable? I read somewhere that silicone may sometimes be used?

                Go with the cheap stuff.
                My thread:
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                • #9
                  Re: What is Vermiculite

                  I think if it has silicone in it, it would say so- what does the bag say it's to be used for? I think I saw somewhere here that some vermiculite (or maybe it was perlite) is treated for use in filling block cores. Mine came from a pool supply place. $14 is a good price if it isn't treated.