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Cast dome with 2nd hand arch. Queensland.

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  • #31
    I prefer white because it reflects light better, giving you a good view of what's in the oven. The white contrasts well with the black soot. When the oven approaches pizza temperatures all the black soot will have burnt away., right down to the base of the dome. This is my primary temperature gauge. For roasting or baking I stop firing when the crown of the oven goes white, but the rest of the dome is still black.

    I just noticed that your oven is pretty much level with the garden behind it. As moisture is your enemy once the oven is finished and dry, It would be a good plan to put a drainage channel behind the oven. Moisture wicking into the slab can be quite a problem. Also, if you've not already cast some weep holes in the slab you can drill some in from underneath. You'll feel it break through when you hit the insulation.
    Kindled with zeal and fired with passion.


    • #32
      More work done last week here is the update.

      Formed up the door with xps foam as it was easier to shape than wood. Piled up bricks and sand again to shape the door and gallery.
      Click image for larger version

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      Click image for larger version

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      Here is the result
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      And after patching.
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      Didn't add any colour to the mix.
      My Build


      • #33
        Will start insulation after a week of damp curing. No curing fires yet.

        Ceramic fibre, I have 1 box so what ever that covers. This will be followed by perlcrete 10:1 in 2 x 40mm layers.

        Question: How far down to go with the ceramic fibre? To the bottom of the fire brick or the Cal Sil board? I presume NOT to the slab as to avoid moisture.

        Same with the Perlcrete which I guess goes down to the slab?

        Does the pelrcrete go below the CF at the base up against the CS or should I leave an air gap all around the base for ventilation. The CS sits on broken tiles, I have weep holes in the slab.

        I like this idea taken from another user (and maybe the melbourne firebrick co!) With 0.03 Alu foil flashing and a bead of hi temp silicone around the base. I think this would be better on the outside of the perlcrete? My perlcrete should go to the edge of the slab in places.

        Click image for larger version

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        Flue questions: I plan on using one segment for the flue plus hat. I take that this just sits on top of the arch and is held in place by about 45mm/2" thickness of perlcrete 5:1 (?) and about 300mm/12" high. I have a bucket from Bunnings that will fit perfectly for this job. Does that sound about right. Does the flue sit in a small bed of home brew as well? I'll leave an expansion joint when I render.

        Thanks for all your help on this! Maybe this will help someone else with their oven.

        My Build


        • #34
          Click image for larger version

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ID:	452581 Made some more progress.
          Here insulation on. Ended up using the whole box and got 4 layers on so about 100mm insulation. CF does not reach the slab.

          Also went with the flashing around the base with high temp silicone to seal it up.
          Click image for larger version

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ID:	452582 I am terrible at silicon work!

          Perlite (coarse) and Vermiculite (grade3/medium fine?) went on soon after in a mix of 8:1 GP cement whereby I put a bit more Vermiculite in the mix (5:3 Vermiculite perlite) to help balance out the coarse perlite. Was not easy to apply from the second row and kept crumbling so reduced to 7:1 to help get it to stick. Let the first row set overnight and continued the next day with more success. Also put in a steam vent, out of 25mm/1/2" galvanized pipe which I cut with vertical cuts in the base to allow water vapor in.
          Click image for larger version

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          It has been 7 days of very dry sunny weather which has been great for air drying. No fires yet!
          Render/stucco in the next few days.
          My Build


          • #35
            When the stuff has gone white you'll think it is perfectly dry, but it won't be deeper in. Try getting a cheap garden moisture meter to push into the layer to test for moisture.
            Regarding setting the flue pipe, most builders use an anchor plate. However they require drilling into your refractory and using fixings. Both of these operations are asking for cracking to occur around the holes from thermal expansion as well as corrosion problems if you don't use stainless fixings, plus anchor plates are really expensive and take up a lot of room. I prefer to cut 3 tabs in the pipe so it can be inserted into the hole in the gallery (slightly loose fit to allow for thermal expansion). The tabs can be easily bent to adjust pipe level.
            You have plenty of blanket layers so don't really need insulating capacity from the vermicrete layer, you just want a firm substrate to render against. For others reading this an easier way to get more workability in a very lean vermicrete is to use a little powdered clay which is half the mass of cement and imparts stickiness to assist application. eg 7:1 vermicrete results in a substantially poorer insulation due to the extra mass of cement. eg at 10:1 the mass of cement is around 1.5x that of the vermiculite/perlite combo. At 7:1 it's around double.

            Click image for larger version

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            Last edited by david s; 04-13-2023, 01:26 PM.
            Kindled with zeal and fired with passion.


            • #36
              Here are a couple of pics that might help you
              Kindled with zeal and fired with passion.


              • #37
                Thanks for the info on the flue, it is giving me a bit of a headache. I'll ask more about that in another post.

                I'm looking for render at the moment and was going to use your method of part home-brew render mix and part acrylic PM render "A 4:1;1 mix of sand, hydrated lime and cement is pretty good. I use that mixed with the PM render 50/50 of each with plenty of AR fibreglass fibres randomly mixed for strength enhancement."
                Bunnings seem to be out of the Davco PM render. But they have a Dunlop 20kg Fine Coat Render which is polymer modified. Would this be suitable?
                The missus would really like a penny tile mosaic over the dome. This would enhance the weather proofing as the oven is in the open. Can I do this after one coat of render?

                My Build