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Cracks in dome and steam - Forno Bravo Forum: The Wood-Fired Oven Community

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Cracks in dome and steam

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  • Cracks in dome and steam

    Hi . I finished the dome about 2 weeks ago , insulated and rendered (thin) waterproof cement. After very gradual firings I have increased the length of burn / fire size and now see some fine cracks which leak small amounts of steam i 1 or 2 places. When the fire dies down these shrink and nearly vanish.
    Should i be concerned? as the rendering is thin - should I add another layer?
    Grateful for any ideas.

  • #2
    Re: Cracks in dome and steam

    Sounds pretty normal and far better than many! The water in the cement - and there is a lot - has to go somewhere! Not sure what you are referring to as rendering, but as dry as San Antonio is, I have to keep my dome waterproofed or the dome gets wet. In England you will probably want to maximize your waterproofing!

    Good Luck!
    Jay

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    • #3
      Re: Cracks in dome and steam

      Water plus Heat equals Steam. The fact that your oven is steaming shows that you're still driving water out of it, a process that will go on for a month of so. Small cracks that close upon cooling are entirely normal. Are they in the brick dome (inside) or the stucco shell (outside)?
      My geodesic oven project: part 1, part 2

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      • #4
        Re: Cracks in dome and steam

        It will steam during the curing process. You may also get puffs of smoke during normal use.

        Water is the enemy of wood fired ovens. Refractory mortar is susceptible to water.

        I cover mine with a tarp when not in use during the rainy season and also re-cure it every spring.

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        • #5
          Re: Cracks in dome and steam

          Thanks for the reassurance. The 'rendering' as I call it, is cement stucco or plastering over the insulation layer (perlite cement mix). It is a very thin layer and I was going to add more later just in case any cracks did appear. I assumed that after this length of time the curing would be complete, perhaps I'm in too much of a hurry to start cooking !

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          • #6
            Re: Cracks in dome and steam

            Cracks are simply part of the process. And steam is an indicator you are making progress (until you get steam a year from now and realize you need to dry back out...GRRR! It happens!)

            And once you get to the firings, it feels soooo close. And yet so far! But the time will come! So start preparing!!!!
            Jay

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            • #7
              Re: Cracks in dome and steam

              I prepared today ! Chicken - sausages - bread - Pizza - A real 'cook it all ' ,and see what happens. The cracks have stabilised so on went a few more logs and suddenly the roof was white . I was surprised how quick it was at just under 2 hrs and my first pizza was half an hour later going in. My wife and youngsters finally saw why I have spent so much time on this odd looking lump .
              I wish to thank all who have posted on this great site, I would not have had the courage to tackle it otherwise.
              Last edited by muppety1; 06-28-2009, 01:43 PM. Reason: spelling /grammer

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              • #8
                Re: Cracks in dome and steam

                Originally posted by muppety1 View Post
                Hi . I finished the dome about 2 weeks ago , insulated and rendered (thin) waterproof cement. After very gradual firings I have increased the length of burn / fire size and now see some fine cracks which leak small amounts of steam i 1 or 2 places. When the fire dies down these shrink and nearly vanish.
                Should i be concerned? as the rendering is thin - should I add another layer?
                Grateful for any ideas.
                How do you think the render allows steam to exit when you have effectively created a barrier? Render should be applied after the dry out.
                Last edited by Johnny the oven man; 06-28-2009, 05:32 PM.

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                • #9
                  Re: Cracks in dome and steam

                  I put a small vent through the stucco into the insulation at the top of my dome. This allows steam/moisture to escape.

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