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42" Pompeii Oven in Jamaica

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  • #76
    Do you think that render was still quite wet?
    My 42" build: https://community.fornobravo.com/for...ld-new-zealand
    My oven drawings: My oven drawings - Forno Bravo Forum: The Wood-Fired Oven Community

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    • #77
      I don't think so. I had it sitting for about 3 days before starting the cure fires. The cracks are mainly around my chimney with is only a single wall, so I assume that's the main reason for them.
      I operating under the assumption that once the curing is done, I can do another render to fill whatever cracks there may be.
      My Build - 42" Pompei Oven

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      • #78
        "Drying" and "curing" are two different things. Curing is a chemical reaction. Portland based masonry products should be allowed to remain moist for at least a week to properly cure in order for it to achieve some of it's final strength. (28 days is best) Then it can be allowed to dry.

        If it were mine, when I made the repair, this is what I would do.

        Remove the rendor/stucco back from touching the single wall pipe so there is no heat transfer. Cut a short piece of larger diamenter galvanized pipe to make a very short section of double wall. (Trimming the Render/stucco layer back enough to insert it slighty may be easier than scribing the bottom of the outer pipe to fit). Insulate between the pipes. Render/stucco up to near the top of the outer section. Then purchase or fabricate a storm collar to place over the intersection of the two pipes.

        You can do a search of the forum for "storm collar" . That should pull up some examples.
        Joe Watson " A year from now, you will wish that you had started today" My Build Album / My Build

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        • #79
          "Drying" and "curing" are two different things. Curing is a chemical reaction. Portland based masonry products should be allowed to remain moist for at least a week to properly cure in order for it to achieve some of it's final strength. (28 days is best) Then it can be allowed to dry. "

          Hi Gulf, glad you posted this, I dislike the the term curing as it's used in the curing thread, because it gets confused with damp curing of various types of concretes, renders/stuccos and mortars, where the objective is to retain sufficient water for a period to allow for the hydration process to enhance strength. I much prefer the term "water elimination" as the drying fires applied to an oven on completion never reach high enough temperatures to change anything chemically, all we do is remove the mechanical water.

          Regarding the cracks surrounding the flue pipe on the outer shell, this is a common problem if the render/stucco is formed directly around the pipe. Because the steel of the flue pipe is way more conductive than the stucco that surrounds it then it will expand first creating stresses in the stucco. If the pipe is surrounded with some box cardboard and the stucco worked up against it, then it can be removed leaving a gap of around 5mm which can be filled with high temp silicon. This seems to do the trick, allows the pipe to expand a little and eliminates the cracks which can otherwise create an entry point for water.
          Kindled with zeal and fired with passion.

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          • #80
            Thank you both for the advise. Feedback like this is why I love this forum and its members.
            I don't want to stop the process now. I just got a infrared temp gun and fired up to 500o F today; 3 days left until 800o F. I can make the repairs in the future by either one of these recommendations or purchasing a double walled chimney; we'll see...
            Last edited by wthwaites; 01-11-2021, 05:19 PM.
            My Build - 42" Pompei Oven

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