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Door/roof height ratio 63 or 55%

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  • Door/roof height ratio 63 or 55%

    hi everyone,

    I am having a go at building my own pizza oven but doing a gym ball with vermiculite.

    My gym ball is 75cm, but have raise it a touch so height of my dome is 42cm as opposed to 37.5cm.

    After lots of reading I was happily building but then a video popped up on YouTube when the guy who has built a fair few said that rather than use a ratio of 63% he was suggested to use 55% for vermiculite oven as they don't reach as high a heat?? This is the first I have heard of 55%, video attached for reference. Some guidance would be appreciated. Thank you skip to 5min 20sec

    Apologies if this posted on the wrong section but I'm new to this.

  • #2
    The standard recommendation of oven door height for a properly built pomeii style oven is 63%. However, I have no recommendations for this method of building other than to not build it. Here are some past threads covering this poor design.
    Last edited by Gulf; 05-03-2020, 12:39 PM.
    Joe Watson " A year from now, you will wish that you had started today" My Build Album / My Build


    • #3
      I read one guy had to add a second floor and the outcome was that the door : dome height ratio become 1 : 2, i.e. 50%. He said it was more difficult to light up, but once hot it worked fine. Go with the 63 % door height.

      Cast a shell insted. Even if a cement-vermiculite would work for some time, it will be a lot more difficult to control the heat. The thermal mass acts as a battery that is charged when the fire is high and radiates back more when the fire is low. Therefore, it is a lot easier to ceep constant temperature. I made a light weight steel barrel pizza oven some years ago. It was fun for a few times, now I'm building the foundation to a proper wfo.


      • #4
        Have you started yet. If not step back and reconsider using the gym ball with vcrete dome. Review cast domes with dense refractory or home brew refractory. Vcrete should only be used as an insulator. 5 to 1 under dome, 8-10 to 1 over dense refractory or home brew dome. Use a sand mold instead of gym ball. Look under "other oven types" in the blog. There are a couple well documented builds. We see these so call one-off YouTube videos that are not in your best interest. On this site you have the collective experience of hundreds of members and builders.
        Last edited by UtahBeehiver; 05-03-2020, 02:30 PM.
        Google Photo Album []


        • #5
          the video you linked to is the first time I’ve seen any one report about the perlite dome’s long term use. I must say I was surprised, as I suspected it wouldn’t last that long. Apart from longevity the lack of thermal mass and vulnerability of a low strength casting are major considerations. If you don’t intend to do any retained heat cooking I guess this is ok, but everyone who owns a WFO discovers the versatility of being able to cook a huge variety of foods in varying ways. Baking bread, slow roasting, fast roasting, smoking and grilling, so a WFO can become way more than just a pizza oven.
          Which ever way you go please document your build here so we can all learn. We are all here to push the envelope, break the rules and share information, in a supportive manner.
          Kindled with zeal and fired with passion.


          • #6
            not what was I was expecting. ‍♂️

            So thank you all for your comments so far..serious food for thought. So to answer a few questions yes I have just started making the template, supplies accumulated and about to start in anger. This is something I have been thinking of doing for a while and finally taken the plunge. Wish I posted on this forum sooner.

            Petter and utahbeehiver I was having same thoughts about the thermal mass. My wife is a keen Baker and have been dreaming of a WFO so it would be put to good use.

            I will check out castable domes and see if I can adapt what I have so far and still use the gym ball but cast over it. More thinking and research to do. Castable Refractory cement is 35 per bag here for 25kg. Will need to see how much I need and what the over weight will be. I was intending for it to be mobile. Ie on a wood frame which moves. Planning to use 75mm timber for the frame.


            • #7
              Do look at the links that I provided above. david s has provided some great insight into the pros of casting in place vrs. the cons of the medicine ball method. Also look for the "home brew" recipe. It is a lot cheaper than the commercial castable refractory.
              Joe Watson " A year from now, you will wish that you had started today" My Build Album / My Build


              • #8
                Originally posted by Gulf View Post
                Everyday I learn something new from you guys, I didn't know how to search directly in google by using the keyword "SITE: "
                Thanks Gulf !