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  • #46
    Re: Curing strategy

    Now, to the new technique recently updated, and practiced. I believe that after the 4th cure, at 600 temp day, for 10 hour sessions, totaling 40 hours into the curing process, that I may (or may not) have answers to help others for crack prevention. This also applies to the building process, which leads to the curing cracks that I believe are impacting me.

    I thought I had a disaster on my hands when I saw the spider web of cracks on the outside dome, and the 3 cracks along my arch, one on each side, and one up top. I believe my approach to building the oven was careful, with consistant mortaring of bricks, using patience and practice. I thought that by just applying a thin amount of mortar to the outside dome (1/4 to 1/2 inch) it might help the bricks to limit movement. I did not mortar or add support to the outside of the arch sides. For the dome, the bricks all crossed bricks below with middle point positioning. I believe that the Refmix mortar I used was well worth the cost, it did not break up or crumble meaning that heat in the area was right for the environment during the COLD and snowy winter, and no bricks are cracking. What I did by packing each bricks sides, keeping the bricks moist, then moving to the next brick allowed strong bonding between brick and mortar. The weight of the dome is also great and limits movement due to pattern of bricks laying upon each other with great balance. I built my arch with the idea of having an angle for looks, but I also attempted the best way to keep strength as well.

    Now for the cracks, I look at where the cracks are and believe I may know the answer.

    A: Dome cracks are only showing on the outside, not on the inside. I believe that due to the shell of mortar and expansion, that it was a waiste at this time, but after the curing process would be possible. The bricks were well mortared together and needed to bond with moisture being driven out. No cracks are going into the dome, none are going through bricks. I believe I would have none, or fewer crack concerns upon exterior of dome if I would have waited with this detail.

    B: The arch has cracks along the wall which I believe is because of limited weight with no true mass of supporting bricks above. Looking at the dome, lots of weight is balanced by brick upon brick, altered upon each other. My cracks on the sides occur after the 3rd brick up which prepare for the arch to meet the wall. There is no real weight at the front face area either, just one brick above.

    C: The arch at the top center is also full of exposure with no support above or on the sides.

    D: For the arch, so much is expose to the cool outside compared to the dome, and the heat measurement at the arch is approximately 30 percent of dome temp. To me, this is where the root issue is to be answered.

    When dealing with heat expansion from within the oven for 10 hours plus at 300, 350, no issues occured to the dome or arch. Upon entering the 500 temp, the heat finally reached the outside dome and arch enough to allow varing heat to create the varying expansion of bricks while the mortar cured. Being that they have different heat affecting the cure, I believe that seperation of bricks and mortar resulted. I also believe that if I did a rectangular arch, My issue may have been prevented as well. The curves of the arch seem to expose curing differences and weight balances during the cure, that I believe were the cause of the cracks. Now, this is a new practice, and I am merely documenting the details. Am I wrong, who knows, I am not a mason, I have only built one oven.

    Tomorrow is day 5 with 10 hours of 700 temp. I may or may not have further issue with cracks. I may or may not have cracks on the inside of the dome.

    Once the curing process is done, I will then go into the plasma state where my oven will once again be tested with a new dimension of heat. I may go up to 900 for a couple hours for a few sessions, and do some foods. This will not be long hour curing temps, just heat temps. After a few sessions, I will then go to Plasma state and saturate the bricks to allow for pizza. I will likely do my first pizzas on Sunday, April 13th. Saturday is wood day.

    I can only hope this detail helps someone?
    An excellent pizza is shared with the ones you love!

    Acoma's Tuscan:
    http://www.fornobravo.com/forum/f8/a...scan-2862.html

    Comment


    • #47
      Re: Curing strategy

      David..........I can see where you are coming from with this. It would make sense to initially go up to cooking temps more slowly and therefore limit rapid expansion. Unfortunately most are not going to be maintaining fire in the oven so the heat/cool cycle must continue. Members have reported improved performance many firings after the curing period. Clearly driving out moisture continues quite some time. I don't feel that a lot of the cracks we are seeing are avoidable given expansion coefficients but neither are they detrimental to performance of the oven nor in most cases appearance, IMHO.

      Someone once said ........"perfection is a journey, not a destination". Long may we all share it.

      Comment


      • #48
        Re: Curing strategy

        Inishta,
        Heartily agree. I don't think it is possible to eliminate fine cracks entirely. Theyre there and the open abit when firing but they disappear when the oven cools and they dont seem to get any worse. So what ? What would you expect when the whole structure expands so much. It doesn't affect the performance. All ovens and kilns for that matter have cracks. In fact that is precisely why the ovens are made of bricks so the cracks can occur at the joins where you want them to.
        Kindled with zeal and fired with passion.

        Comment


        • #49
          Crack science

          Originally posted by Xabia Jim View Post
          David, but I could be bass ackwards,

          From my days making ceramics and pottery I remember that bisqueware is usually dry. As I recall wet bisquit will surely crack. Neat analogy to WFO's
          Thinking about this further, bisque firing was done at lower temperatures, then the clay was glazed and fired at higher temperatures. Bigger items have more of a tendency to crack than smaller ones.

          From my days as a Geologist I learned that clays were 40% air space (sand is more like 25%) so in drying a clay, it takes a long time because it's comprised of tiny microscopic plates all jumbled up.....drying clay shrinks and cracks but potters are able to make crack free clay vessels.

          We cycle our ovens during curing, but could a steady increase in heat be even better?.......searching for the VMO
          sigpicTiempo para guzarlos..... ...enjoy every sandwich!

          Comment


          • #50
            Re: Curing strategy

            The recommended cure rate for castable refractory (which is the same material essentially, as fire brick or refractory mortar),is (for our WFO wall thickness) 50 C/hr I .believe that this is a good guide for a curing stategy. Simple enough
            Kindled with zeal and fired with passion.

            Comment


            • #51
              Re: Curing strategy

              As I have cured my oven, the drop in temperature from the previous night is not great. How do you answer this into the maintains heat concerns? Is going down 40% in heat overnight that significant, i.e. 600 cure yesterday, to waking up and starting with 397 degrees? I agree that it would likely be best to maintain a heat to drive out the moisture, but that will be the next generation, correct? I believe we are on the right path. If we do not have the heat maintained, which would have to be wood free, then we have the next beth method right now.
              An excellent pizza is shared with the ones you love!

              Acoma's Tuscan:
              http://www.fornobravo.com/forum/f8/a...scan-2862.html

              Comment


              • #52
                Re: Curing strategy

                OK, now for my final documentation on curing. I say it is the best method until shown otherwise. Yes, I had cracks. The best thing with this method is that it allowed me to bond with the oven, and I know that sounds wierd. I mean bond by acts of knowledge. I can now use the wood in a constructive manner to heat up the oven, maintain heat, increase, balance, and know saturation. All this during curing process. Could I have prevented cracks, I already wrote my details earlier on my thoughts regarding this. Would I build another oven, YES! I will likely build a smaller version for my in-laws from ACOMA. Life is short and special, so try it, love it, soak it in. This was a special moment in my project life that allowed me to do something I thought I could not do. I did this all myself. Oh ya, this is about curing. Wrap yourself around this new method, it will help so much.
                The end!
                An excellent pizza is shared with the ones you love!

                Acoma's Tuscan:
                http://www.fornobravo.com/forum/f8/a...scan-2862.html

                Comment


                • #53
                  Re: Curing strategy

                  Like a great wine, you also have a great finish Robert. I'm glad to hear that you're happy with the results. Embrace you're oven, give it a big kiss. (Keep your tongue in your mouth. They don't taste that good!)
                  GJBingham
                  -----------------------------------
                  Everyone makes mistakes. The trick is to make mistakes when nobody is looking.

                  -

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                  • #54
                    Re: Curing strategy

                    KISSSSSSSSSSSSSS. Ohh how sweet that was

                    I am sooooo happy!

                    Finished the oven at 1:30pm Saturday with a 30 minute 900-950 burn. I then go out at 7:30am this morning to check retained heat temp. Guess what? It was at 453 degrees, wow! Of course I forgot to check the floor temp, this was dome temp. Approx 65% retained heat 18 hours later due to the 700 cure day. I still have more insulation to do
                    Last edited by Acoma; 03-23-2008, 09:35 AM.
                    An excellent pizza is shared with the ones you love!

                    Acoma's Tuscan:
                    http://www.fornobravo.com/forum/f8/a...scan-2862.html

                    Comment


                    • #55
                      Re: Curing strategy

                      Originally posted by david sewell View Post
                      I use one of those gas rings with a long braided metal hose attached to a 9Kg LPG gas bottle, set it at 1/2 throttle and let it burn all night. It doesn't go over 200 C which is safe. We use the procedure to dry out clay work in our kiln prior to biscuit firing to avoid steam explosions. Gas flame is the best for eliminating water. I then light a wood fire and keep it gentle by using heat beads. Build up slowly until all the damp patches on the outside stucco are gone then build up to 400 C. Hope this helps.
                      David
                      I am using your method to cure my oven at the moment and it working great - thanks!. I am about to go into day 3 and the temperatures of the floor, dome and air are rising slowly but surely almost exactly as recommended. I have only just started my second 9 kg bottle of gas with the burner still at 1/2 throttle. May need to crank to full throttle if the temps stop rising. Very little maintenance required which is a bonus.
                      Also, I would like to try Eucalyptus because it is just so abundant in Australia but it seems to be getting a bad wrap. What is your experience with it? I also have access to some very old gidgee posts (100 years approx so it should be well seasoned). Have you or anyone else used it? Apparently it burns incredibly hot and for a long time so may need to try a little to start.

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                      • #56
                        Re: Curing strategy

                        I'm pleased the gas ring worked well for you. I'm sure this is the best method yet. Slow, gentle and even temp rise. Way to go.
                        On the wood- the best wood is free wood. I think we must have exported all the crappy eucalypt varieties to USA Iv'e never heard or experienced any problems here in Oz. Have heard gidgee is really good to burn, but you'll need to split it up and That sounds like work.
                        Kindled with zeal and fired with passion.

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                        • #57
                          Re: Curing strategy

                          Mieno, If you've been heating for three days I'd be switching to wood to take it the rest of the way up.
                          Kindled with zeal and fired with passion.

                          Comment


                          • #58
                            Re: Curing strategy

                            Originally posted by david sewell View Post
                            Mieno, If you've been heating for three days I'd be switching to wood to take it the rest of the way up.
                            David

                            I will switch to wood in the morning but the temps just keep slowly rising on the gas. The floor and side of the dome are at ~300C with the top of the dome ~350C. I found a site that has a good curing section Curing a Traditional Woodfired Oven
                            They use heat beads. Would you go from gas to heat beads then wood?
                            Where are you in Australia by the way?

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                            • #59
                              Re: Curing strategy

                              I would go straight to wood (not too much vicious flame) and the heat beads too ( say 3 handfuls) Around 50 C/Hr rise should be safe. Do you have any damp patches on the outside ? Sounds like it's going perfectly Thanks for the link I'll check it out. We're in beautiful Townsville.
                              Kindled with zeal and fired with passion.

                              Comment


                              • #60
                                Re: Curing strategy

                                Originally posted by david sewell View Post
                                I would go straight to wood (not too much vicious flame) and the heat beads too ( say 3 handfuls) Around 50 C/Hr rise should be safe. Do you have any damp patches on the outside ? Sounds like it's going perfectly Thanks for the link I'll check it out. We're in beautiful Townsville.
                                No damp patches but I can't recall ever seeing any. I have a refractory concrete dome then 5 layers of ceramic blanket then chicken wire and render over. Should I be seeing damp patches? Also, have you tried that step down method to start your fire?

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