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  • Dome exterior too hot

    Hi all

    Iíve googled for hours without successÖ If anyone can help, that'd be wonderful.

    My ovenís exterior seems way too hot. About a month ago I finished a 1.07metre (internal diameter) brick oven, with the following insulation:

    Dome - 75mm ceramic fibre blanket (3 layers) followed by 50mm concrete render (the first 20mm is perlite mix - my 100L bag ran-out!)

    Base - 100mm ceramic board (2 layers), on top of 75mm Hebel. The floor is overkill, I didnít want any heat going into the suspended slab, and risk it failing.

    Nine days ago I started curing the oven. For the first 3 days I ran at 50 degrees c, the next 2 days higher, but below 100C. I kept the fire running for 5 hours each night. I ramped it on the 6th day. On the 8th day dome started to clear, even though I didnít plan to bring the temp up that high. So I thought blow it, and ran the oven hard. Itís the 9th day, and its very easy to ramp the temp up. I have no cracks inside whatsoever, not that I can see anyway. I two small cosmetic cracks on the render surrounding the arch, but they appeared before curing.

    So all is good, except the exterior is hot enough to be uncomfortable towards the top third of the dome.

    Thereís no steam to indicate water, and no cracks thatíd indicate steam trying to escape. So why is my domeís exterior still uncomfortably hot?

    I would've thought if I cleared the dome (twice), that all the moisture would be gone. I live in a dry and warm area.


    Thank you

    Brian

  • #2
    Forget the no cracks... This morning found crack on the back centre, extending from the bottom, zig-zagging along the mortar up five chains. The joins are tight, so I have no idea how i'd repair it, or even if its a pro blem. The crack is only on the inside, the exterior is fine.

    And here is a pic! Obviously before I started the curing fires. Since then I've installed the flue, and put it through the shed roof. Once its cured, the shed will go.

    Click image for larger version

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    thanks
    Brian
    Last edited by kayakfisherman; 04-02-2018, 10:48 PM.

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    • #3
      Just about guarantee it is still wet mate

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      • #4
        Agree, your oven is still wet. As youíve correctly observed the oven is way hotter at the top than the bottom. This is also an indication that the top of your oven inner bricks are dry, but the ones on the base are not. This situation leads to a big difference in temperature and therefore thermal expansion and often leads to cracking. There may also be a persitent ring of black unburnt soot around the base of the dome on the inside which is also further indication that the oven is not properly dry. The remedy is to keep firing, but you should also avoid the fire from hell until that black ring disappears. The steam accumulates in the insulation and carries the heat as water is quite conductive. When the oven is dry the outside will be only cosy warm. Many builders incorporate a vent in the outer shell to release this steam which hastens the drying of the insulation, but you will eventually dry the oven without it.
        Kindled with zeal and fired with passion.

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