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Dome Insulation and finish.... - Forno Bravo Forum: The Wood-Fired Oven Community



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Dome Insulation and finish....

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  • Dome Insulation and finish....

    Hello all,
    Well.... the dome and door are finished and drying out for a week before i start the curing process. I have the ceramic blanket ready...

    I seek advise as to the best 'recipe' for the vermiculite [or perlite] insulation layer that goes over the blanket and any tips in appyling this layer, as i heard it can be a little tricky. How thick? How to apply? Use just portland cement? Add sand to mix too ?

    Lastly the final render.... any tips for this?


  • #2
    Re: Dome Insulation and finish....

    Hi Phil,

    The Forno instructions for the vermiculite layer work well. I think I did 10 parts perlite/Vermiculite to cement, mix dry and add water (not too much) just enough so that the cement coats the vermiculite. It is like a thick porridge.
    I made a form tool out of ply about 60cm long by 20cm on a cut out thicker piece of ply. This I held in place and shovelled the mix behind applying pressure toward the dome while compacting it into place from above. There is a photo of a similar tool on one of the Australia posts.
    I worked around the dome in 200 mm strips allowing the lower course to cure a bit to support the upperlayers. As height increased I allowed the lower layers to fully dry before continuing to avoid a collapse.

    Most of this layer I did at about 75 mm on top of the 50mm blanket. I did two layers of render, only two small cracks.

    This insulation prevents a large amount of heat loss. The inside of the top of my dome can be at 500C+ after a few hours and the outside only at 28C.

    Good luck

    Last edited by BOOMERS WFO; 09-09-2013, 10:07 PM. Reason: Post to soon
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    • #3
      Re: Dome Insulation and finish....

      Insulation over the blanket (which is obviously insulation) is not required. It does no harm but you could just apply a stucco render and be done with it, assuming you are building a dome.
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      If at first you don't succeed... Skydiving isn't for you.


      • #4
        Re: Dome Insulation and finish....

        The advantage of using a vermicrete layer over the blanket is that it enables you to get a nice shape. There are lots of lumps and bumps where the blanket folds or overlaps. If you don't do a vermicrete layer you end up having to make the outside shell much thicker in an effort to get the hemispherical form. The vermicrete layer also insulates of course.
        Kindled with zeal and fired with passion.


        • #5
          Re: Dome Insulation and finish....

          Originally posted by Les View Post
          Insulation over the blanket (which is obviously insulation) is not required. It does no harm but you could just apply a stucco render and be done with it, assuming you are building a dome.
          I agree render over the blanket it not only quicker than dealing with a layer of pearlite/cement. Time is also saved waiting for that pearlite to dry.
          Downside is that the pearlite/ cement is cheaper than an extra inch of ceramic.
          Decision ultimately is yours fourlambs you can't wrong either way.
          Regards dave
          Measure twice
          Cut once
          Fit in position with largest hammer

          My Build
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          • #6
            Re: Dome Insulation and finish....

            Based on your original question, I did install a perlcrete layer over a ceramic fiber blanket. Used a 5 perlite to 1 portland mix. I wanted it a little more robust since I was going to stucco next and then drill in fasteners for copper singles (BTW which I have not done yet). I wanted a fairly consistent shape for the shingle base. Attached is pic of a curve trowel I made to pack and form the pcrete. Also Ignore the foil covering on the CF blanket. General consenseus is not to use. My CF blanket came that way so I punched hundreds of holes in foil so moisture could migrate out.
            Build Link............... Picassa Photo Album Link


            • #7
              Re: Dome Insulation and finish....

              Snow is coming soon Russell! Gotta see that copper. I might get down to SLC this winter for some boarding. I'll have to come check on you.
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