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Not enough cal sil insulation - what to do?

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  • Not enough cal sil insulation - what to do?

    I might not have enough cal sil insulation.

    I have enough to lay under the floor, but not enough to fill it under the layer of 50 mm of homebrew. Is it a problem to build the homebrew layer directly on concrete? I figure there might be some heat loss? Check the picture to understand what I mean.

    Of course I will also insulate with rockwool or superwool and vermiculite/portland on the homebrew. But the hombrew layer will not have any insulation underneath.

    Is the only solution to buy more cal sil? Expensive shit.

    I have 1200 mm x 510 mm cal sil board and my plan is to do 800 mm ID oven.
    Last edited by Linuc; 05-02-2021, 02:57 AM.

  • #2
    Do NOT place the cast dome on the concrete hearth, it is act as a heat sink. You can pour a 5 to 1 pcrete ring or a full layer around or under the CaSi. Also Rockwool is not you best dome insulation, too soft and absorbs water to easily. Ratio for pcrete for dome is 8-10 to 1.
    Attached Files
    Last edited by UtahBeehiver; 05-02-2021, 12:49 PM.
    Google Photo Album []


    • #3
      Thats a good choice, or make it easy this time and just get the second board. Everything will be dry, nice and level. You will thank you're self for that investment later on in the build.
      Last edited by Petter; 05-02-2021, 10:17 AM.


      • #4
        Thought so. I'll buy another board!


        • #5
          Make an insulated door with the leftover if enough.


          • #6
            Originally posted by Petter View Post
            Make an insulated door with the leftover if enough.
            Good idea.

            Instead of starting a new thread. Is 25 mm ceramic blanket enough for insulation? And then 50 mm of perlite/portland. See the attachmented file.
            Attached Files


            • #7
              The calculations tell that a ratio of 1:2 to 1:3 is the best compromise between mass and insulation for a given thickness. In theory, they should be equal, but since heat retention time is constant (within some 90 %) across the given ratios, less mass and more insulation heat up faster with less wood.