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Starting new build ~32in Gas homebrew castable

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  • #16
    Had to spend another 60usd or so on mineral wool + perlite, concrete.
    I added around the base and sides to get an area to build up the walls. Kept falling down so had to push the side in with hand as well as flatten with tool to make areas that the next spot could fit on. Got almost half way up and it would collapse, so gonna leave it a day, then finish most of the sides to near the top.

    I shoulda bought larger 1" role of insulation in the beginning, but instead i bought three 2in sheets that are like 80cm x 1.2m or something... Anyway. I did read to add some metal wires into the cast for the insulation to.stick (or the front face, can't remember,) and I did too, it kept the insulation down, I didn't put enough though, and the insulation was a bit too thick. Good to know for next time.

    It's been a week since the cast. I added the insulation yesterday and a few inch area to build up the perlite cement, I added another layer today around most sides, I'm approaching limit of the walls near me so will be thicker and more insulated on one side and top vs other side.

    I'll try to start fires in a few days I hope. Not sure how long I need/should let the percrete dry for, I recall others doing it in layers and then leaving it for a week... Though I also read when you have an Insualtion layer then percrete it doesn't matter as much as the water can escape through insulation.

    I'll leave a few days then do the outer cement render layer except for around top, as I want any steam to escape. Right now there will be near 2in + ~4in of percrete. Can't remember the number of buckets ratio I used today so I'll post again when I count it tomorrow.
    Attached Files


    • #17
      Probably going to need another 85L bag of perlite or even 2. Most of sides Click image for larger version

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ID:	456016 are around 3in+ but still not done in a few areas on top and front.

      Need to figure out the decorative arch thing, and a stove pipe...

      The percrete is around 8-10:1.

      Put some hydrated lime with the cement and found it went a bit better. Also had left over burn out fibers and fiberglass so added a bit of those too.

      Maybe another bag of perlite on around it and can start sealing with cement+sand layer.


      • #18
        You will increase the probability of cracking the outer shell if you cover the damp vermicrete or perlcrete with a sand cement layer because the moisture can lead to steam expansion issues, particularly at the base of the dome where the moisture will be driven off last. When the stuff goes white you'll think it is dry, but it will still be moist deeper in.Get a cheap garden moisture meter that can be pushed deep into the vermicrete. Don't render until it registers as dry.
        Kindled with zeal and fired with passion.


        • #19
          Can I start the cure fires before the final render layer, and remove the steam? Last 4 nights I've been adding layers of percrete in sections, and covering with plastic, there should be one more I think or two. Then I'll let it air out a while, always hot and dry here. Was going to add a pipe at a couple locations, just a 4" steel or even abs one to remove any steam that gets into the rock wool later.

          I have a the moisture meter I use with Arduino stuff, but it's the short one so I'd need to buy another. From the other 4in I did, it takes more than a week to look dry.

          edit: had the cover off last few days, still damp, going to be a while, also still trying to find a cheap chimney. One option is 4 100mm sq steel bars together, the surface area should be alright, and long and cheap enough. seems no one has chimneys in saudi arabia lol, too hot i guess.
          Last edited by AlPizzaMan; 10-16-2023, 12:18 PM.


          • #20
            Ok starting curing fires today. Had a low fire last 2 hours and dome is now around 250-290F, going to see if I can keep it in another couple hours.

            Tomorrow I'll try for 350 or so
            Then next day 400
            There was a forum post I saw recently on it that's old but still applicable.

            ​​​i don't have outer render on. Outside dome temp is ambient still, no increase After 2 hours. I'll put render on it (maybe) after 4 or 5 days


            For the chimney, I calculated my area of (18+15/2)*9.5 for the door area trapezoid in inches. 10% of that for a chimney area is around 16insq+. I got some 8x8x8 inch clay, which inside is about 5.5x5= 26+ sqin.

            Right now it's only 4 pieces high or 32in, I'll see if the draw is enough. I was going to put 3 and then another meter steel pipe but the clay is cheaper.

            Still not sure on the arch decor. Thinking some 3 or 5insq light marble I have. Get some mortar or use cement and the trowel and stick some pieces on before the render layer.
            Last edited by AlPizzaMan; 10-21-2023, 11:20 AM.


            • #21
              I see some condensation coming out of the vent I have that touches the rock wool,.and goes through the perlite, some visable drops at pipe top. Now top of oven outside is 150F while inside is 290-300F. After it's cool tomorow I'll take a look inside top. Can't tell if one spot has a crack in top of dome or if it popped when I went in the house for a while.
              took a vid before but hard to compare, both look same. Maybe just steam let off

              After a few days of this I'll get to know if the heat can climb more without any condensation, and the heat loss through top is ok. Worst case I add another couple inches of perlite on top before render and rewait
              Last edited by AlPizzaMan; 10-21-2023, 12:02 PM.


              • #22
                Up to around 700 today, 115F at hottest point on top. Still little bit of condensation on the air pipe that touches the mineral wool and vents out past the percrete.

                Might try some pizzas tomorow. Base of oven not heating enough I think. While roof is 700 floor is like 400, I saw a few posts where people would have a diff of 100F or so.


                • #23
                  It is the big difference in temperature that causes problems because it results in a big difference in thermal expansion. That is why it is good to allow the oven to return to ambient temperature before starting another fire. A persistent ring of black around the base of the dome on the inside is an indication that there’s still moisture there and it’s at this point that you don’t want to ramp up the temperature too high. If you see visible steam, you are going at it too hard, back off.
                  Kindled with zeal and fired with passion.


                  • #24
                    Had it for a couple tests.
                    HArd to get floor temp above 650 and harder to keep the temp up. Might need more wood. Tried the gas for warming up, then alot of heat with wood/coal. Also tried a natural gas burner to keep temp after the firing.

                    ​​​​​​Maybe will try one more time with more wood and let it go for 2 hours. Insulation is working ok on top. High temp in, low temp out, except around chimney. Few light cracks in the outer render, not worried

                    I drilled about 7 8mm or so holes throigh my concrete slab into the percrete to see if a difference second pizza test but not. Maybe just need more heat not sure.
                    If third time heat is not up, will get another layer of bricks or will add 2 inches more percrete after taking out the brick floor, then reinstall bricks.
                    ​​​​​​Right now it's 2inch concrete slab, almost 4" percrete 6:1, little leveling sand and 8mm tiles to flatten. 2.5in red clay bricks on top, but s couple fire bricks. Tried both no diff yet. By what I've seen my insulation is not little compares to most and there was no feeling of heat with my hand under the concrete slab. Makes me wonder is ther water somewhere or.... I made about 10 pizzas today and the heat just kept dropping.
                    TO'Day gas heat almost 1.5 hours to 450f floor 650f ceiling or so, then an hour of maybe 3kg of wood,.but floor temp 650, ceiling white and 800+. After first 5 pizzas I put a gas burner in the side and cranked it up cause the bottom was just done while tops getting almost burnt.
                    Any advice welcome. Thanks


                    • #25
                      "ceiling white " after two and a half hours sounds typical of the drying fires required to purge the oven of moisture. Be careful now because impatience leads to damage. Don't try to hurry it, but do try to avoid too much flame impingement on the oven roof, because it will be dry while lower down it will still be moist (see post # 23). Flame can be reduced by using charcoal fuel. It is also helpful to allow the oven to cool back to ambient temperature so the difference in temperature between oven parts evens out and you can start another fire. A persistent ring of black around the base of the dome indicates moisture still there. Underfloor moisture is the hardest to eliminate because heat rising by convection in the oven chamber will work on rising the temperature at the top of the dome first.
                      Last edited by david s; 11-19-2023, 12:12 AM.
                      Kindled with zeal and fired with passion.


                      • #26
                        Hey Al,

                        You're doing it! I'm enjoying following along. I might have missed it somewhere along the line -- where are you located?

                        I hope it's going well, and you add more photos. There's a lot to learn from your project. Thanks!


                        • #27
                          Hi guys, sorry for the lack of updates, got busy, and this has been used about 7 times so far plus the days of heating long ago without cooking. I finally figured it out, I think.

                          I think I need to make a video, incorporating the pics, and the time required, and materials. Took a good 30 or so hours of building, then you have to wait after every step.

                          Anyway, ive tried wood, natural gas, and both at diff times, gas to heat, then wood to sustain, and the opposite way. By far i think the easiest is to set and forget a gas burner (a bit dangerous, need sensors and what not) anyway. Ive tried the pure Neapolitan with no oil or sugar, and it is very doable, the issue is that, it took about 5 firings with cooking for many hours, perhaps to get out the moisture and have it "hold heat" a bit more. Right now i still dont have a door, I use an aluminum covered cardboard. Anyway, after like 4 hours and 4 or so kg of natural gas I have around 750 floor sustained, and after 1.5 or so hours of cooking its settling around 550 and can still cook a pizza in a few mins that was made with about 5 grams of sugar and some oil in the dough. I just tried this last weekend. Maybe will fire it again.

                          Something I could not find any details on yet was heating time, tho I think my oven, for 32in is not that efficient, maybe its just lacking insulation, or maybe i am not heating it enough yet. From what I can see, my construction is slightly unique on this forum due to the tiles on the percrete, and then the dome frame on top of it. After that it was several inches of percrete, and then 2 render layers which were sand+hydrated lime+cement. Im thinking to paint it but unsure. Here are some pics.

                          If I redid anything, one would be not to wet the percrete at any time after making it, and maybe adding a bit more insulation. The rockwool I used were the 3x5 feet sections or whatever, without the foil backing and were very hard to manipulate, then the percrete on top... Takes so long for each thing to dry. I put 2 plastic/pvc or whatever pipes out the top back of the oven for moisture to go out, and often steam would come out. Last weekend though the oven was so hot smoke was coming from one side, I guess the temp got that high in the insulation.

                          As I said, I think i can make a video about the chimney and other stuff doing, the fastest, cheapest way possible with squares of fire clay. Something else which was not discussed here or youtube much is about the clay bricks (not the firebricks) was that they generally are not suitable and may have issues. So far after cooking for 7+ times they are fine (you can get 7 of these for the price of 1 med duty firebrick), Im not doing commercial scale, just about 13 pizzas each time and oven temp recently was 750F floor, with ceiling above 1k. On wood the temps are much higher, but I need natural gas for decent continuation, otherwise its just a massive amount of wood.

                          1 issue, I dont have a proper door yet, I think thats raising my heat loss, didnt get around to it yet. Soon.
                          Attached Files
                          Last edited by AlPizzaMan; 01-24-2024, 09:50 AM.


                          • #28
                            One thing to mention, I havnt done any roasts of any kind, and dont feel any want or need to, much easier in conv oven and set and forget, even though I made this oven a few inches higher on the sides... havnt baked bread either which I would like to try.

                            I can fit 2 pizzas in at a time (maybe 3 or even 4 if using only natural gas - maybe ill try a speed run next time, see what I can squeeze out of it) but, last week at 750 for a while cooking, I couldn't complete making two pizzas fast enough before the first one needed turning before the second one was in, and then I could just take it out. I think the oil/sugar in the dough 6 hours before baking made them cook faster, as previously the temp needed to be 850 or so for similar browning. Fun experimental stuff.

                            however, I thought about this later that night, the way to do 2 or 3 in, is to shape and top all the pizzas fast, while they are not sticking to the marble, then throw each in the oven in 20 secs each or less. That way in around 3 mins they are done at these temps. Soft, crispy, and airy, slightly chewy. Best pizzas ever.

                            One thing in my oven, and I guess any. After the floor is in and the walls. If you want it "shorter ceiling" just add another layer of bricks and boom, you are up almost 2 inches. I placed my bricks inside, on sand, after making my homebrew casts sitting on tiles on percrete, purposefully.


                            • #29
                              Your pizza looks great! Once you get a door made you got to try roasting some meat. We do chicken, pork roast and beef all the time, There is nothing like pulling out a well fitting door and having a big cloud of aromatic steam billow out. The way the oven can simultaneously brown and tenderize meat seems to be way different than an conventional oven.
                              My build thread