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  • #61
    Re: Oven opening size

    Hi Frank - The 'vermicrete' insulation is just vermiculite and cement. A ratio of 8:1 by volume works ok.

    The trick is to get the moisture level right and too much water is an issue. It will end up like wet rice bubbles and is not a 'fun' material to work with. I found that working from the bottom up, balling it up and applying it in one 'smear' and moving on worked for me. Messing with it after you place it caused grief in the form of crumbling away.

    I had chicken wire over the blanket and it helps hold the vermicrete too. It is perfectly stable once it hardens but I found it an 'interesting' medium. I did, however, use it on subsequent builds.

    By the way, it is best to mix it in a barrow with a hoe rather than a mixer. The vermiculite maintains its integrity that way and you can better judge the moisture level. Good luck with it.
    Cheers ......... Steve

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    • #62
      Re: Oven opening size

      I've found the correct ratio of water is 3 parts water for every 10 parts vermiculite, although if you have the fine grade you need more water. As the addition of cement decreases the insulating capacity drastically I use a 10:1 mix, vermiculite, cement. Any less cement than this makes it difficult to get a good workable mix. Adding a little powdered clay to the mix will help to make a lean mix more workable.
      Kindled with zeal and fired with passion.

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      • #63
        Re: Oven opening size

        Cheers thankyou!
        Also I'm building the chimney vent out of bricks. What size would be best to make the internal diameter of it.

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        • #64
          Re: Oven opening size

          Originally posted by FrankHawkins View Post
          Cheers thankyou!
          Also I'm building the chimney vent out of bricks. What size would be best to make the internal diameter of it.
          Depends on the size of your oven.
          A 24" oven needs 20 sq in
          A 30" oven needs 30 sq in
          A 42" oven needs 50 sq in
          Kindled with zeal and fired with passion.

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          • #65
            Re: Oven opening size

            Ok, I think it's 8x5 inches at the moment. So I may have to open it up a little as mine is a 39 inch oven.
            Here are the pictures of my opening. Does it all
            Look about right?

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            • #66
              Re: Oven opening size

              From another angle.

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              • #67
                Re: Oven opening size

                Originally posted by FrankHawkins View Post
                Ok, I think it's 8x5 inches at the moment. So I may have to open it up a little as mine is a 39 inch oven.
                Here are the pictures of my opening. Does it all
                Look about right?
                That's ok, just make the cross section of the chimney a little bigger. The restriction at the bottom where the smoke enters will just work as a venturi making the smoke accelerate at that point.
                Kindled with zeal and fired with passion.

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                • #68
                  Re: Oven opening size

                  Building a 32" oven. Dome height is 16". Oven opening is arched. 12" in the centre arched to 9 1/2" to the sides. Width is 18". I'm worried that height (at 75%) is way off the mark. Should be around 10.5"...BUT if I add a row of half block then it gets really tight on the ends...
                  Any thoughts? Apparently I missed the 63% rule in the plans!? I figured it was ball parked etc etc...

                  I only looked into this today after completing the arch and it just looks to big....

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                  • #69
                    Re: Oven opening size

                    Don't sweat. It makes far less difference than many people would lead you to believe. Just fire your oven as it is, you'd find no noticeable difference if you rejigger it to 63%
                    Kindled with zeal and fired with passion.

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                    • #70
                      Re: Oven opening size

                      Glad to hear this! Since its arched from 9" (not 9 1/2" like I said earlier) to 12" I can take comfort in the math that it averages out 10 1/2" of height..which is right on the money

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