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Silicone in pearlite - 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.

Ask Me Anything New Forum Feature

You will notice a new forum at the top of the main page called, "Ask Me Anything". This forum will be used for live one hour "Ask Me Anything" (AMA) sessions hosted by people who are knowledgeable in different areas pertaining to wood fired ovens. How it works:
- Each AMA will have a "sticky" thread where the community can post questions they would like answered during the live session. This will allow everyone to participate even if you can't be online for the live session. These questions will not be answered by the host until the live AMA; if you need an answer quickly, you should post it in the appropriate Forum area for the community to respond.
- Another thread will be posted for the live AMA. Registered users who are logged in during the live session can interact with the host by asking questions and receiving responses.
- The live thread will remain in the AMA forum to view after the session.

We hope you enjoy this new feature! Please let us know if there is a topic that you'd like to have as an AMA and we'll look for a host!

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Silicone in pearlite

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  • Silicone in pearlite

    Why is it important to use pearlite without silicone for pearlite cement insulation? If you look in the Pompeii Oven instructions under Hints and Tips They caution against using pearlite with silicone added and recommend using "horticultural grade pearlite". Can someone explain why? I can source the masonry grade with silicone easily. Getting the other requires me to order and ship.

    Thanks Tom

  • #2
    Re: Silicone in pearlite

    The thought is the portland cement will not bond with the perlite (or vermiculite) due to the silicone. Since the mixture inherently has a somewhat crumbly texture when hardened, you wouldn't want something in it to compound the crumbly nature.

    Not being a chemist or engineer and having not tried the silicone perlite, I have no idea if the silicone actually effects the bonding or not; but it certainly makes sense that it could.

    RT

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    • #3
      Re: Silicone in pearlite

      Perhaps the silicon addition for masonary grade perlite is an attempt to prevent extra absorption of water into the perlite grains.
      Kindled with zeal and fired with passion.

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      • #4
        Re: Silicone in pearlite

        I believe that someone used the stuff successfully: Why don't you ask your vendor for a sample (explaining the problem) and do a test. After a week it should be hard, the consistency of cork, and only a little crumbly around the edges.
        My geodesic oven project: part 1, part 2

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        • #5
          Re: Silicone in pearlite

          Can't speak for the silicon perlite, I only used horiticultural, but I also used attic-insulation (silicon) vermiculite and didn't have too much trouble. It is true that while mixing it up with portland and water sometimes the portland would slide off exposing the golden vermiculite, but I just mixed it up more thoroughly and stopped messing with it.

          Seemed to work fine.

          My biggest problem with perlite was that even the most modest mixing rapidly destroyed the perlite, rendering it as fine dust. The vermiculite stood up to the abuse of mixing much better...and I mixed very gently: giant wheelbarrow, long gloves, slowly churning the mixture up to my elbows without any tools. That's as gentle as it gets.

          I would go vermiculite for that reason alone. Silicon or not doesn't seem to be an important deciding factor to me.

          Cheers!

          Website: http://keithwiley.com
          WFO Webpage: http://keithwiley.com/brickPizzaOven.shtml
          Thread: http://www.fornobravo.com/forum/f21/...ttle-7878.html

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          • #6
            Re: Silicone in pearlite

            It doesn't matter if it turns to dust, the essential property is the same. Siliconized perlite is useless for gardening, but it doesn't really matter for this application.

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            • #7
              Re: Silicone in pearlite

              Surely if the grains break down to dust you will end up with an increase in density, because each grain is filled with a lot of air. Certainly when mixing it and this happens you end up with a reduced volume which is in turn an increase in density. This is the main reason I prefer to use vermiculite rather than perlite because it doesn't break down as easily and does not produce that irritating dust.
              Kindled with zeal and fired with passion.

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              • #8
                Re: Silicone in pearlite

                Thanks for the replies. This will be the second oven I built. I work at a Vocational school in Central Mass. and I am designing this one for the students to construct at school. I would like to get the materials from one local source to make it easier for the future owner. On my oven I contained the concrete/pearlite mix within the hearth by pouring the hearth with a circular form two inches off the bottom the diameter of the dome plus insulation. It worked fine but I ordered the horticultural pearlite on line. It is much easier to have the future owner set up an account at a local masonry supply than have to depend on them to order something on line and then waiting for a delivery. It makes scheduling the project easier on our part.
                Unless someone has firsthand knowledge I guess this may be a non starter. By the way what happens to the silicone when it reaches a temperature of one thousand degrees? Any chemists out there?

                Thanks Tom

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