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Vermiculite 4" 5" 6" Does it matter? - 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.

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Vermiculite 4" 5" 6" Does it matter?

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  • Vermiculite 4" 5" 6" Does it matter?

    I searched but I couldn't find an answer.
    Does it make any difference whether I use 4" or 6" of vermiculite/perlite insulation under the floor? Is there any downside going with 6" as far as placing bricks on top? I understand the R value will increase but is it better than going with the recommended 4"?

    Thanks!
    George

    My 34" WFO build

    Weber 22-OTG / Ugly Drum Smoker / 34" WFO

  • #2
    Re: Vermiculite 4" 5" 6" Does it matter?

    I think it was Dmun who said, you can have too much thermal mass, but not too much insulation. I have 5" under my floor.
    Eric

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    • #3
      Re: Vermiculite 4" 5" 6" Does it matter?

      I guess what I'm trying to ask is will there be any 'settling' as you go thicker? I know it has good compressive strength but over time will they eventually settle somewhat under the weight of the oven?
      George

      My 34" WFO build

      Weber 22-OTG / Ugly Drum Smoker / 34" WFO

      Comment


      • #4
        Re: Vermiculite 4" 5" 6" Does it matter?

        "I guess what I'm trying to ask is will there be any 'settling' as you go thicker?"

        No. A vermiculite/perlite/portland mix will not settle to any appreciable degree.

        Comment


        • #5
          Re: Vermiculite 4" 5" 6" Does it matter?

          Thanks Neil, that's exactly what I wanted to hear.

          On a related note, is it all right to place the vermiculite/portland mix over a freshly poured slab, giving, say, a couple of hours setting time in-between?
          George

          My 34" WFO build

          Weber 22-OTG / Ugly Drum Smoker / 34" WFO

          Comment


          • #6
            Re: Vermiculite 4" 5" 6" Does it matter?

            'Back in the day' when I built my oven, it was recommended to pour the insulation layer the same day as the support slab. The idea being - the slabs will bond together better. As we all know, nothing is going anywhere once it is all built, so the bonding theory is debunked. Many have waited a day/week between pours, since those original instructions were posted.
            It is entirely your call based on time and energy level, take a day or two off, or go straight to the insulation layer.

            RT

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            • #7
              Re: Vermiculite 4" 5" 6" Does it matter?

              Thanks RT, that's exactly what I thought. I can do both on the same day as there will be no re-forming to do. The insulating layer will be formed exactly like the slab.
              George

              My 34" WFO build

              Weber 22-OTG / Ugly Drum Smoker / 34" WFO

              Comment


              • #8
                Re: Vermiculite 4" 5" 6" Does it matter?

                I would wait a day or two. I would then check that there is no dishing or ponding on the new slab and fix it with a bit of grinding. You want the vermicrete layer to drain out if any water gets in.

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                • #9
                  Re: Vermiculite 4" 5" 6" Does it matter?

                  To the original question. It is a (non) simple engineering question to calculate, but the reality is that 4 to 5 inches will probably not become heat soaked (thus requiring more depth) in the time frames we are operating the ovens.

                  As for the compressive strength, my brick chimney is sitting on up to 24 inches of 8-1 perlcrete and I have no concerns of settling at all.

                  Comment


                  • #10
                    Re: Vermiculite 4" 5" 6" Does it matter?

                    I decided I'm going to instead use an insulating board over the slab as I found a local dealer who sells 2" and 3" boards in 24"x36". The 3" boards are less expensive (per sheet) than the 2" boards. The 3" boards are more dense as well (per cu/ft). Are they not as effective as 2" boards?
                    George

                    My 34" WFO build

                    Weber 22-OTG / Ugly Drum Smoker / 34" WFO

                    Comment


                    • #11
                      Re: Vermiculite 4" 5" 6" Does it matter?

                      I must admit, I've been confused about the density of insulating materials as described on FB. Intuitively, I would have assumed that less dense means better insulating, but 6# blankets are regarded as better than 4# and worse than 8#, so that just doesn't make any sense to me.

                      With regard to the boards you found, what kind of board are they? What are the specs?

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

                      Comment


                      • #12
                        Re: Vermiculite 4" 5" 6" Does it matter?

                        Originally posted by kebwi View Post
                        With regard to the boards you found, what kind of board are they? What are the specs?
                        Here they are:

                        Ceramic Fiber Board

                        I'm confused as well...
                        George

                        My 34" WFO build

                        Weber 22-OTG / Ugly Drum Smoker / 34" WFO

                        Comment


                        • #13
                          Re: Vermiculite 4" 5" 6" Does it matter?

                          I see your point. My theory would be that the manufacturing process for the less dense material is significantly more difficult and expensive, but that's just a theory. Maybe the denser stuff is in much higher demand, thus is produced in much greater bulk, thus driving its price down.

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

                          Comment

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