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My First (hopefully last) build - Cast Refractory

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  • #16
    Re: My First (hopefully last) build - Cast Refractory

    Arch fitted.
    Joining faces were chamfered to provide a channel for insulation fill.
    Used some cementone fire cement to seal the inner joint of the arch/dome, about an 8mm gap. Checkd with manufacturers (Bostik) who reckon this stuff is good for pointing up to 14mm, so we'll see.
    From outside the 8mm to 25mm chamfered joint was backfilled with vermiculite/sifted refractory mix.
    If this crumbles - the fire cement should hold it in. If the fire cement crumbles also - plan B (which I have yet to devise!).

    Fitted a 7" flue pipe (3ft length). Experimenting so just used some tin foil jammed around it as a seal.
    Had a firing - almost all smoke drawn straight up the flue from cold.
    A few wisps out the front of the arch, but nothing much, and the whole flue arch is only 10" deep. Still not fitted a decorative arch yet, so time will tell.
    Arch did not get very hot and it was a fair sized fire.
    How much insulation would anyone recommend for the flue arch??


    • #17
      Re: My First (hopefully last) build - Cast Refractory

      Originally posted by pikemonkey View Post
      How much insulation would anyone recommend for the flue arch??
      It's the dome and floor in which you want to retain the heat, so as your flue arch doesn't get as hot anyway I think you only need enough insulation to act as an expansion joint so the expanding arch doesn't crack your outer shell. I don't use blanket over the gallery, just vermicrete.
      Wow, you're going really well. I just checked when you started, less than a week and you're firing already. Folk who cut bricks often take over a year to build an oven. You don't have to convince me that a cast oven is way faster. What is your internal diameter?
      Last edited by david s; 03-29-2014, 04:12 AM.
      Kindled with zeal and fired with passion.


      • #18
        Re: My First (hopefully last) build - Cast Refractory

        Switching to metric - internal diameter is 1 metre. (39 inch appx)
        All door opening ratios taken into account,
        Been a bit slack with the photos - will follow this up soon.

        As said before - I work on ships, normally rotate 5 weeks away with 5 weeks leave.
        So I suppose I have an advantage there over weekend oven builders, since I've been at it all leave. Away this week so been racing the clock!! Decoration will continue next leave, but oven is functional.
        The ground slab was in place 6 months ago.

        Had a couple of additional curing fires, then went for it yesterday afternoon!!! First pizza party with some neighbours - The Christening!!

        350degC at the floor to cook pizzas. 400+ around the dome Heat up time, about 1 1/2 to 2 hours.

        Cooked pizza, then ran it as a gentle open fire when the British evening chill set in.
        No more fuel added after 1900.

        Made a temporary "Blue Peter" door from one of the MDF forms, some tin foil, and some batten.

        Oven temp this morning at 0800 was 180deg C dome and floor.

        Outside of the dome reached 55degC in some places when at full temp and saturation. So I might add another 1" layer of vermecrete, or even some domestic insulation blanket. (The vermicrete will be easier, since it will be the final, painted rustic dome finish).

        With the floor bricks saturated to 350 degC, underside of lintel base measured at 19 degC.


        • #19
          Re: My First (hopefully last) build - Cast Refractory

          Ceiling insulation compresses very easily which makes it hard to render against. Sounds like your oven is performing pretty well. Expect it to do even better after several more firings.
          Kindled with zeal and fired with passion.


          • #20
            Re: My First (hopefully last) build - Cast Refractory

            Cheers David, I'm happy with it so far.

            Since all the newspaper from the dome forming was well and truly incinerated last night I can now see the inside surface of the dome better. A bit hot to stick my head right in at the moment but only really seeing a couple of cracks which correspond with those from my over zealous curing before. Not affecting performance.

            The fire cement I used to fillet the arch was a bit cracked at the arch top - expected that, can be touched up.
            I noticed the flue arch was hairline cracked through before firing yesterday. Reckon this was done on moving it/removing the formwork (which was stubborn). But the arch is stable and self supporting.

            Lessons learnt - a touch more patience required on the curing maybe.
            Otherwise it is working fine, and I have room to improve dome insulation if required.

            Planning to paint over the vermicreted dome, or put another layer of vermicrete on using white cement (snowcrete).
            Any recommended coating/paint for sealing the outer surfaces when done?


            • #21
              Re: My First (hopefully last) build - Cast Refractory

              It has been interesting to follow your build. I have a notion of building a portable oven one day and there is much to learn from others who are learning.

              My dome is brick and finished in the usual way brick-ceramic fibre-mesh-vermicrete-render. I coated the render with Dulux Acratex as in the pic. As the name suggests it is an exterior acrylic texture finish. This was applied with a very coarse roller and left a slightly dimpled finish. You could vary the texture of the finish depending on the roller you use. Covers the minor imperfections and is waterproof. I am sure that you will find the equivalent in Essex.

              Congratulations on your progress.
              Cheers ......... Steve

              Build Thread

              Build Pics

              Forno Food Pics


              • #22
                Re: My First (hopefully last) build - Cast Refractory

                Thanks Greenman I'll look it up.
                Away to work tomorrow or wednesday, so the cement mixer's off back to the hire shop today, and a tidy up of the garden!!!

                Had another pizza party yesterday. - Stoked the fire up a bit. 550+degC at dome walls, 450degC on the cooking floor. 1 1/2 hours to heat up, probably less than that but I had to wait for the inferno to go out - bit too much wood on the fire!!!
                I should take into account that the oven was preheated from the evening before and was still sitting at 100+degC yesterday afternoon.
                The crack in the arch opened up a bit, about 2mm as expansion took place, but arch was solid. Closed back up after firing , when the oven dropped to about 350degc.
                No more cracks anywhere else.
                Disappointed about the cracked arch - I am sure this happened on removing the form work, should have been more careful.
                But it's very stable, provides a natural expansion joint and eventually will all be covered up. (I just know it's there!!)
                I can always make another arch from remaining fire bricks at a later date, but probably won't.
                All I need now is some of that Aussie climate!!!!!


                • #23
                  Re: My First (hopefully last) build - Cast Refractory

                  Great work,
                  how about posting some pics.
                  Kindled with zeal and fired with passion.


                  • #24
                    Re: My First (hopefully last) build - Cast Refractory

                    On their way. Waiting for my phone to upload to google drive.


                    • #25
                      Re: My First (hopefully last) build - Cast Refractory

                      Not done a bunk on the photos.
                      Called back to the ship early!!!!!
                      Sailing at the moment.
                      Can't upload photos on satellite internet - way too slow.
                      Should get into a port over the next few days and hopefully will upload them via my mobile.
                      Missing the family, the dog and the oven!!


                      • #26
                        Re: My First (hopefully last) build - Cast Refractory

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                        So here's the oven with cast vent arch attached, 7" 900mm flue inserted (loosely and sealed with tin foil until I fit a permanent stub adapter.
                        Note the temporary door made from a piece of my MDF form covered in tin foil. Lasted two days and is now crumbled at the top, but served it's purpose for pizza party and baked tatties at suppertime!!
                        You can also see the crack in the arch, and a bit of smoke staining.

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                        Side view of the oven.

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                        Tatties ahoy!! Keeping it simple.

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                        Taken Tuesday morning just before going to work.
                        Now coated with a 1/2" layer of blanket and vermicrete.
                        The arch shape is a bit ragged since I'd cut up the original form which got stuck when I cast the arch. So propped up some plywood offcuts with bricks to keep the vermicrete in place.
                        It will all straighten out with a grinder and have a les "plump" appearance....

                        I have a heap of large sandstone slabs left from patio project, so will be using this to face the arch and as a landing and worktop around the oven.
                        But that.s all another month away.
                        Got a good workshop where I am, so working on the door here.