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  • #16
    That's a very interesting chart.

    Seems the big jump from 4/1 to 3/1 is the sand component

    What are your thoughts about the refractory cement recipes from the link for the dome?

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    • #17
      It is only the very top (2 mm or so) of the vermicrete layer, in direct contact with the floor bricks that would be susceptible to temperatures high enough to degrade the portland. Because of all the air in the mix the temperature drop off as it gets deeper is sufficient for the Portland to survive IMO. Judging from pulling the spy hole plugs from kilns it is the tip of insulating refractory that may be bright orange hot (approx 1200 C) while the base of the plug, around 100 mm long, can be held in the hand (just).

      There is an error in the table for the 5:1 vermicrete compressive strength. It should be 175-225. You are correct in assuming the sand has a big part to play in increasing strength. As a rule of thumb if you double the strength you'll halve the insulation value. The 5;1 ratio has proven adequate for both strength and insulation value for under the oven. For over the top, because it is not supporting weight, a much leaner brew can be used. I use 10;1 but anything leaner i find too hard to apply and it still needs to be firm enough to render against. If you are not concerned about it being insulate you can make it richer.

      Calcium aluminate cement (CAC or refractory cement) in conjunction with perlite will produce an insulative mix. IMO a dense, rather than insulative mix is required for the dome so it has adequate strength as well as thermal mass, a requirement to store heat. You could use it for the under floor insulation mix, but i think you would be wasting your money as the portland /perlite or vermiculite mix has proved to be a good solution for many oven builders.
      Last edited by david s; 06-15-2018, 04:32 AM.
      Kindled with zeal and fired with passion.

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      • #18
        Thought I'd lay out the brick work for the floor:

        Which presented the next problem. The thickness of the dome Insulation will dictate where the floor starts so as not to fall off the back of the stand.

        Can Vermicrete be used as an insulating layer without the FB and if so how thick does it have to be?


        Last edited by Hysteric; 06-23-2018, 01:12 AM.

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        • #19
          David S mentioned in his previous post the up to 10-1 can be used on the dome. IHMO 3-4 inches is an adequate amount without a CF blanket. Although CF blanket is more efficient it is not mandatory.
          Russell
          Build Link............... Picassa Photo Album Link

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          • #20
            Originally posted by UtahBeehiver View Post
            David S mentioned in his previous post the up to 10-1 can be used on the dome. IHMO 3-4 inches is an adequate amount without a CF blanket. Although CF blanket is more efficient it is not mandatory.
            Thanks Beeehiver.

            After looking at it i would imagine that the amount used for the vermicrete insulating layer below the floor would be also needed to insulate the dome. Considering that there was $150 in vermiculite and about 50$ in cement it doesn't really make sense to go that route when the FB will cost around $240. Not to mention that work involved and clean up.

            I noticed in another thread some where David mentioned Rock Wool instead of FB. Might be worth a look .

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            • #21
              The CF board is a better insulator vs p/vcrete per inch thickness. I only mention p/vcrete since your original post indicated you were on a budget. Vermiculite must be very costly in your area to be similar in cost to CF board. I don't believe David S is an advocate of rockwool since it will absorb water more easily.
              Russell
              Build Link............... Picassa Photo Album Link

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              • #22
                Everything is expensive in Australia!

                The Vermiculite costs about $30 for a 100 litre bag.

                Is the FB just for its insulating porposes?

                What about alternatives like this:

                It has a Thermal Conductivity of (ASTM C 518-10) 0.0345 W/m.K


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                • #23
                  This link only goes to the general site and not a specific product. There are two other components necessary for a suitable floor insulation, one is temperature rating (should be at least a 1000 F) and compressibility rating at cooking temps, ie 90-100 PSI at 500 F. the of course K rating.
                  Russell
                  Build Link............... Picassa Photo Album Link

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                  • #24
                    For the Dome

                    Try this:

                    JH_HardieFire_datasheet.pdf
                    Attached Files

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                    • #25
                      I am unfamiliar with this product, if for the dome, then the compressiblity factor is a non issue. Having no knowledge of the product I can't say yeah or nay
                      Russell
                      Build Link............... Picassa Photo Album Link

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                      • #26
                        Ok guys its been a while as "Life is what happens while you're busy making other plans" I'm hoping to get stuck back into the oven over the christmas break. I have decided to go with the home brew method so want to clear up some issues. What would be the best sand to use? Link down at the bottom for sand types.



                        I need to use it for both the dome as well as the mold.

                        Also is Portland cement just a generic name for cement in general?
                        Last edited by Hysteric; Yesterday, 11:20 PM.

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