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  • #16
    Some people have created a heat gap to separate the oven from the outer arch portion. Most stuff the small gap with oven gasket material/cord and/or high temp flexible sealant (usually a silicon based product). The gap doesn't have to be very large...1/4" or 1 cm at most. There has been a fair amount of discussion on whether the effort makes a significant difference in heat retention. My personal opinion is that you're going to lose most of your stored heat through the door interface and in terms of increasing your long term baking just doesn't make enough difference to my normal baking schedule. I like the idea of building a little gap into the "joint" simply to accommodate some of the expansion/contraction differences in the dome structure/vault during use. But again, my oven doesn't have an expansion gap and I don't miss it. I just butted my arch structure up to the oven with my high temp mortar and I'm not suffering or having any regrets after 9 years of use putting 5,425 pounds of dough (pizza, cookies, bread, etc.) and plenty of meat/pasta/vegetable meals through the Dragonfly Den oven.

    Bottom line for me is for you to do what you feel comfortable building. It's worth what you think it's worth. If you want an extreme, heat retention oven...a well constructed door is number 1 and the insulating gap #2 (after plenty of base and dome insulation ). If you just want to make pizza and bake bread on a weekly basis, don't stress on the gap...insulated oven surround and door are the primary things to "worry" about (again IMHO). If you are worried about needing an expansion joint, then build it in...but there are plenty of working ovens that don't have an expansion joint. Again, it's really about what you feel is the right thing to do for your comfort level.

    Relax, it's your oven and based on what I see in your build, it will work very well and you are going to totally enjoy it "with or without the heat break/gap".
    Last edited by SableSprings; 03-23-2018, 10:04 AM.
    Mike Stansbury - The Traveling Loafer
    Roseburg, Oregon

    FB Forum: The Dragonfly Den build thread
    Available only if you're logged in = FB Photo Albums-Select media tab on profile


    • #17
      A small gap of 1/4”” or so will do little to prevent substantial heat transfer. You would not expect an oven with 1/4”” of insulation under and over it to operate wel. Although even some slight separation of dense conductive material will reduce heat conduction, if not heat radiation, quite a lot. We bang on about the importance of insulation yet this area gets omitted in many designs. The main purpose of the gap is to provide an expansion joint. I’’ve seen enough cracked decorative arches and outer dome shells in ovens, including the first oven that I built, without this feature, to convince me that uneven expansion is the culprit. If the design can totally isolate the the inner oven from the outer decorative arch and oven igloo shell then cracking in these areas is eliminated. If building a dog kennel style then part of the problem is reduced.. Some place this joint between the inner oven and flue gallery in an effort to reduce heat conducted into the fluegallery. In my build it is between the fluegallery and the outer decorative arch.
      Last edited by david s; 03-23-2018, 12:17 PM.
      Kindled with zeal and fired with passion.


      • #18
        So today the keystone'(s) went in. Not as cleanly as hoped but in none the less.

        Pulled out the sand mould and got in to do some cleaning. Not the most exciting part thats for sure.

        Was quite a few gaps inside so pushed some mortar in the best I could, don't know if necessary but did it anyway. Time to start planning the front landing and the flue. First though get some ceramic blanket and get fire in there, (even if just a little one for show).

        Certainly not the prettiest oven inside, but as longs as it cooks a pizza and doesn't fall down, i'll be happy.


        • #19
          Slightly more clear shot of inside. Are the little gaps ok or do they need filling with mortar?

          Trying to decide on how to shape the landing. Current plan is to have the bullnose bricks set as is following the curve of the slab. But I'm not sure how it looks. In person I think it looks a little weird, but in photo's ok? Opinions please. The flue will somehow tie in with this shape at least at the bottom, but as with all things will be figured out as I go.

          If I go with the curved front my plan is to smooth it out with concrete polishing pads like those below( if link works). Does anyone have experience with these? I only have a high speed grinder, will they just fling off at that speed?

          Perfect for Granite, Concrete, Marble, Stone, Tiles etc. The velcro backer/pad holder are with water feed hole, can be used for wet polishing. Aggressive and Durable made with quality Diamond Powder impregnated in Resin. | eBay!


          • #20
            photos for above post.


            • #21
              SO its pretty much done.

              Got the flue arch and front landing done. Still need to put in a chimney. Haven't finalised the chimney design yet though.

              3 layers of ceramic fibre blanket topped of with some perlite concrete.

              Then a very little ceremonial fire.

              First real curing attempt the other day using lump charcoal. Thought while its going we can at least cook some fish and baked potatoes.

              Have had a bit of trouble maintaining consistent temps. First firing was going nicely at about 200'C, started to drop so threw on some more coals, and up she went, my temp gauge was of the dial at 280'C and the bricks were reading from 250'C to 450'C going up the dome. No internal cracking though, but a few on the perlite. Not worried about that though, its more or less there just to finalise the shape before final render coat.

              Another fire tonight with some more roast veg and pork.
              Temps a bit more consistent tonight sitting around 200'C air and 250'C to 300'C wall. Although did get some nice flames early on. Looked pretty cool.

              The hopeful plan is to really fire up on Saturday night for the first pizza.


              • #22

                Well done Shane Im inspired and about to start
                CHEERS Bruce


                • #23
                  Nice job well done.
                  Cheers Colin

                  My Build - Index to Major Build Stages


                  • #24
                    Hopefully i can get started on my mark 2 oven around august. Miss my oven heaps. Went to mates last night for wood fired pizza and it was so yum. Not as good as mine of course LOL
                    Cheers Colin

                    My Build - Index to Major Build Stages


                    • #25
                      I'l eventually get around to some update photos, but it is pretty much done. And has had some good use.

                      I have a question about making a door.

                      My plan is to make a hollow door from stainless and fill with some of the leftover perlite I have. The hollow section will be about 50 - 100mm thick, probably somewhere in the middle. The questions is would 1.2mm stainless steel be thick enough?

                      Something like this.


                      • #26
                        Actually the thinner the better as long as it hold shape and can be welded. Even SS has a high thermal conductivity value (K) but certainly better than aluminum or carbon steel. I used SS filled with CaSi. It is 1.5" thick and If I were to do again maybe 2" plus thick but then weight becomes an issue.
                        Google Photo Album []


                        • #27
                          Have you checked out this thread? This is a good one Deejayoh started, and if you do a search there are a few more that talk materials and thicknesses.
                          My build thread


                          • #28
                            Originally posted by JRPizza View Post
                            Have you checked out this thread? This is a good one Deejayoh started, and if you do a search there are a few more that talk materials and thicknesses.
                            Which thread?

                            Disregard, found it.


                            Last edited by shanesmith80; 07-17-2018, 06:04 PM.