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  • My attempt to a a build

    Ok, figured I would get this in the right location after making a couple other post in getting started.
    Here's where I'm at with my first attempt to build one of these things and a few explanations.
    The base is a bit large, actually very large but it gives a place to stand and eat also. I built it to hold a 42" oven with five inches of insulation, and added a 6" overhang on the slab because I was going to brick the sides, but wife decided she had rather have stucco it and I only built a 36" oven on it. Why, a 36"? I was going to build a 42 out of fire brick, but to cut cost, I changed it to 36". Well, then I decided to build it out of castable since I had plenty of that, and my mind set was on building a 36. Half way through casting pieces, it dawned on me I could do the castable in a 42".without the extra cost, but then decided I didn't feel like going through all that work to start over casting pieces for a 42"
    The base is similar to FB's design, made with 2x2x1/4" angle iron and 5/8" rebar through it in both directions every foot. The top frame was drilled so the rebar passed through it to within 1/2" of the edge and 5/8 rebar all the way around the edge. Every cross joints are all welded for extra strength. The reason for the 5/8 rebar, I had several hundred feet already on hand so I used it. To make everything fit, I made the slab 2 3/4" thick. You could probably park a M! tank on top of it.
    Since I'm going to be throwing firewood underneath, I put 3/4" plywood around the sides and a divider in the middle with doors on both end. It's so big, I Didn't feel like crawling 6ft in with the spiders to get to the back of it for wood.
    On top of the slab you will see a 1" cement base for the IFB and the sides are drilled every 6". This was to get the IFB up off the slab so potential leaks around the bottom of the stucco won't get to the IFB. Also a way to anchor the metal lath around the bottom when it's installed.
    I will be installing 3" of high grade Fiber blanket (Maxwool HTZ 8#) around the sides and the top 1/3 of the dome will have 4".
    My stucco is on order since there is none to be had locally so it's going to be a few weeks before I can install it.
    The high temp mortar is used to seal the joints was air dry and not really intended to be installed as thick as I did so I'm using my fish cooker to hold it at 160 degrees until the mortar dries.
    The wire you see in the side is a K Type thermocouple that's sticking approx. 1/4" through the hot face inside. There is also a 10K thermistor between the IFB and the slab just so I can see how well the IFB insulate.
    The black box is my PID controller I built for my coffee bean roaster but it works great for reading my temps here also.

    I cast this oven with 3" thick dome and 2 1/2" thick floor from industrial castable refractory. I think there are about 15 or 16, 55 pound bags of it in the dome and floor. The floor is in five sections in and effort to try keeping it from cracking. The dome is in four sections, also in a effort to prevent cranking. All joints in the dome are spaced at 1/4" Each section of the dome weighs approx. 130 pounds. I do a lot of bread baking so I wanted more mass to help hold the heat and hold it fairly steady. I also made provisions for a gas burner and a steam line in the slab when I poured it. The steam line will be installed for baking, the gas burner, probably not but figure it would be almost impossible to get a 4" hole through that slab after the fact with all that rebar. I only did the slab, not the IFB or oven floor, those I can drill from the bottom if/when the time comes.
    Last edited by BenKeith; 09-16-2017, 07:04 AM.

  • #2
    I built a fire in it today to dry it out so I can put the insulation on it. The oak wood I was using had green leaves on it five weeks ago so it was a pain to burn and get it up to heat in a slow controlled manner. I started at 8:00 this morning and at 6:00 PM it had been at 765F for an hour, so I figured why waste the heat, I cooked a couple pizza's in it. Using a dough on the fly instead of my normal dough that's made a day ahead, I tried Bobby Flay's recipe since it was ready in 1.5 hours. Won't do that again.
    Once I got a coal bed established so the wood would burn, I was pleased at how it came up to heat and how easy it was to control and maintain the heat. Right now, it's at 810F and that's probably about as far as I'm taking it. In about another hour, I'm going to pull the fire out and get it covered.
    The #23 IFB did very well. I don't have a sensor in the floor and I discovered my old infrared sensor doesn't go high enough but after 10 hours, the thermocouple in the side, about 1/2 way up the dome, was reading a steady 710F and the 10K sensor between the IFB and the slab was reading 133F. The durarock under the slab was showing 123F with my infrared sensor.
    I tried some fiber blanket on it and it looks like 3" on the side and 4" on the top is going to be about perfect. After a few hours, it was barely warm to the touch in both areas, With only three inches on top, there was a little more heat loss than I would want. not hot but still a little warm.
    Last edited by BenKeith; 09-16-2017, 05:35 PM.

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    • #3
      Here it is with 80 sq ft of 1" fiber blanket on it.
      The first layer was cut so all joints are snug and overlapped a couple of inches, by taking 1/2" out of each side of the joint so they lay flat and smooth to minimize gaps between the insulation and dome. A good carpet knife is essential for this.
      The second layer was cut to fit snug but the joints were not overlapped
      Third layer I let the cuts lay over the adjacent piece and added the fourth layer to the top.
      Now I will use metal lath to secure it to the dome, as soon as I fined the concrete screws I bought, but it looks like I will be making a 30 mile trip to home depot to get another box.
      Also, I only put 1" over the entrance tunnel.
      Last edited by BenKeith; 09-20-2017, 04:15 AM. Reason: Can't do math, had error is sq ft of insulation.

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      • #4
        I had to add eight more square feet of insulation to it, so that brings it to 88 sqft total. When I put the lath on the way I just laid the fourth layer over the top, screwed everything up and made the most out of shape dome you could imagine. So, after spending 1/2 a day putting lath on, I got to spend another whole day taking it back loose and doing it again. I had to make the fourth layer even all the way around and down almost to the outer most diameter all the way around. Doing this, it made the dome very evenly and well shaped. I still have the very front to lath, as soon as I figure out how I'm going to do that and get the vent pipe set. I will post a picture of the lathed dome when that's done, but that's going to be a few days. I'm going to put the brick arch in and brick the front of the landing before I finish that last little bit of lath around the tunnel.
        I can't put the vent pipe in until I get my stucco or a cover built over it.

        Last edited by BenKeith; 09-20-2017, 04:09 AM. Reason: I had an error on sqft of insulation

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        • #5
          BanKeith, that is an awesome looking oven build. I would love to be able to build something of that quality. Would it be possible to share how you made the molds or forms for the dome and the floor. I would love to be able to make my oven in sections like yours, but I really don't even know how to get started.

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          • #6
            The molds were very basic. I made on 1/4 dome size mold. I layered 1/2" foam board from Home Depot, the stuff with the foil side because it was only $7 a sheet. Each piece was cut on an angle and progressively smaller to fit the contour of the inside of the dome. Then sanded and shaped. Now the funny part, to get a good smooth finish, I used what's very common in middle GA, good old red clay. I just went on the side of a dirt road, scooped up some red clay, crushed it down and sifted it through a piece of screen wire. Added water and mixed until I had a nice paste and using a trowel applied it over my form nice and smooth. Let it dry and they painted it with two good coats of polyurethane. I used 3/4" plywood to make the two sides the size of the outside of the dome, with 1/4" plywood on the bottom. I made 3/4" pieces that screw onto the sides for the overlapping flanges. BE SURE to screw them in from the outside, they have to be taken out to get the piece off the from after casting. Understand, you have to do the math to get the form the right size. Yes, the form is made to produce a 1/4 section with on mine comes down to 18 x 17 high for the Styrofoam, but that's not the size you make the form. You have to figure the overlapping joints and then the 1/4" space you want to have when done. Just to be sure I didn't have fit problems, I cast the last piece with the whole thing assembled and the braced inside and 1/4" space stripes inserted. Casting it for the floor to fit snuggly inside, the pieces have to be almost prefect and I didn't trust them to be that good so that just hedged my bet.

            The floor was done using 1" thick foam from home depot. I stacked two piece plus a 1/2 since I made a 2 1/2" thick floor I cut the center circle first, one piece smaller than the other for my overlapping edge and poured the center first. Then I cut the two pieces opposite each other and poured them with the center piece I poured in place. Next was the back piece and the front piece with the landing section. These were poured with the other three pieces in place. pouring everything with the pieces in place ensure good, tight joints. Just make sure everything is level, the cooking face is down and on a very smooth surface and use plenty of release agent. I was using a cheap shortening. I know a lot of people seem to use motor oil, but that's not something I wanted in something I was going to be eating off of.

            The bad part is I just hauled all that stuff to the dumpster today. I could have take some pictures for you. Also, be aware, I had to repair the clay on my form every time because the castable stuck every time. I tried the shortening, Johnson's Paste Wax and a release agent I use on fiberglass molds, all of them stuck.

            The critical part is getting the castable mix perfect. a little dry and it doesn't pack, just a fraction too much water and it will be impossible to get it to stay on the form while you are vibrating it.

            A little word of caution, make sure you price the materials before hand. The materials I used are not cheap and it might be cheaper to build it with brick. That was about $1,000 worth of industrial castable if a person had to buy it. Some are wanting as much a $4 each for the #23 IFB, I think I used about 40 of those. Approx 90 sq ft of 1" 8# glass wool insulation is another $300 by the time you pay shipping on it. And that's not even getting into the mortar mix, rebar for the slabs and the cost of building the stand. This would not be an inexpensive build.

            Forgot to mention, I used the 1/2 foam to make my entrance tunnel and had that in place when I made the front section
            Last edited by BenKeith; 09-23-2017, 09:44 PM.

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            • #7
              Thanks for all the information, it will help me decide about how much oven i can afford. I would like to start out with a smaller semi portable oven. I plan to use the oven for a couple years then give it to my oldest son when they move into a house; by that time I should have a larger budget to work with.

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              • #8
                I started off wanting to build a 42 inch, and was going to make it out of brick, but had my head up my butt when I started making it out of the castable so I ended up making a 36. I cooked pizza's in it last week when I was doing the initial firing and I could do two 12" pizza's. That's about all I think it will handle. However, with the oven at over 700 degrees, they cooked fairly quickly so it didn't take long to do eight pizza's. Also, I'm no pizza cooking guru so two was about all I could handle at one time. I think if it was any smaller, it would be limited to one pizza or a couple fairly small pizza's.
                As for cheaper alternatives other than size, I couldn't see since in it. Thinking I was going to build me a WFO for a few hundred bucks was what got me started on this idea over a year ago. The more I researched and learned, the more found that was not going to happen. At 70 years old, I only planned to build one and I wanted it right. For the hellassus amount of work involve in building this thing (I've built house that I think took less work) I could not see myself going halfass with the materials or making something guaranteed to crack. I tried to use good materials and build it in a way the gave the least chance of cracking.

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                • #9
                  Finally, the oven is ready for the stucco. Vent pipe is installed, and lath is finished. The vent pipe I made by placing a 6" stove pipe inside a 8" pvc drain pipe and pouring a light weight insulating castable in the space between the two. My wife said the grand kids are having a plaque made to go on the front of it so I made the area above the door larger than it needed to be to accommodate that. That area is also cast in an insulating castable.

                  There are a lot of things I'm pretty good at, brick laying is not one of them and using old deformed and out of shape bricks didn't help..
                  Last edited by BenKeith; 09-24-2017, 11:34 AM.

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                  • #10
                    Another step closer, the stucco base coat is on the oven and three sides of the base, I had all the fun one person should have in one day say I figured I would save the last side for tomorrow. Now I will wrap it with wet towels and plastic for a couple of weeks to wet cure. Slowly, this thing is coming to an end.
                    Haven't decided if I'm going to stucco the vent pipe or just leave it as is Being insulating castable it can't handle water but I ordered the metal to cover it with yesterday. Decided that was my safest bet.
                    If you notice the front landing area of the slab looks different, it's because I ground it down and polished it. Now my wife luvs the way it looks so much, she's asking me to do concrete counter tops in her kitchen.. Also, I'm doing the whole slab, I just used up my 50 and 100 grit pad and ordered a couple more.
                    Last edited by BenKeith; 09-26-2017, 04:39 PM.

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                    • #11
                      Ben,

                      That oven looks mighty fine to me.

                      That is the way it all starts. You build an oven. The wife notices all the skills that are involved. She watches some cable home improvement shows. Then bang! A life time of "honey dos" are added to that ever growing list .

                      I can't really tell from the pics. But, the top of the smoke chamber looks to be a little flat. You may want to think about sloping it some away from the castable flue for a water shed. You mentioned ordering metal. Raising it up a bit to fit a metal storm collar transition will help a lot to keep her dry.
                      joe watson

                      "A year from now, you will wish that you had started today "

                      My Build
                      My Picasa Web Album

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                      • #12
                        Thanks for the response. Yes, when I poured the refractory, it was flat. When I added the one inch of insulation on and lath I tried to give it some angle. You can't tell it from ground level but when the base coat was applied, there is about a 15 degree taper from the pipe to the edge. That was about a 1/2" of base coat and about as thick as I wanted to make that layer. When the brown coat goes on, the plan is to add more taper, hopefully at least 20 degrees. When I install the metal roof over it, I will have to be sure I have a perfect seal. The roof will just be a simple lean-to, higher on the front than the back. I'm actually considering not going through the roof with the pipe and let it vent against the bottom and see what the smoke does. It will be a solid metal frame construction and metal roof so there is no fire hazard, but the soot and heat on the bottom and how it draws might all be more of a problem than I will tolerate. I've also looked at roof mounted vents but I've not seen one that looks like it would have a good draw. So far, the only ones I've seen that enhance the draw all mount on the pipe.

                        After 50 years, my wife pretty much expects me to do most anything she decides she wants to do. It has been 15 years since I remodeled the kitchen and built all the cabinets. She's thinking it's time to update things. She loves her cabinets but thinks it's time to change the finish, and new counter tops. I've been telling her I'm getting to old for all that work, but now that she has seen what I've gone through building this oven, she ain't buying that argument.
                        Last edited by BenKeith; 09-26-2017, 07:56 PM.

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                        • #13
                          if it was me, I would think very seriously about going on through the metal roof. I am sure that you will be glad that you did. It doesn't take very much to cap a flue to keep the rain out.
                          joe watson

                          "A year from now, you will wish that you had started today "

                          My Build
                          My Picasa Web Album

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                          • #14
                            I'm with over 30 hours into curing my oven, I started at approx. 6am Sunday morning. I did and initial curing before putting the insulation on but only for 16 hours. I am using a curing schedule recommended by the manufacture of the castable. For the past six hours the thermocouple mounted inside the dome about 1/2 way up has been around 850f. Using my IR scanner, it's showing 980f in the top of the dome and the hearth is reading 710 about eight inches in from on the hot coals. Taking temp readings with the IR scanner in different places, it looks like this. Center of the dome outside is 124f, side of the dome outside is 107f. Under the center of the slab, reading from inside the storage box is 177f. Even the flue pipe I made with insulating castable is only showing 166 degrees. So, not knowing a whole lot about what it should do, it looks like it's holding the heat pretty good to me.

                            Well, I just ended it. For the last four hours I have it between 980f and 1060 on the thermocouple. The center of the inside dome was too hot for the IR to read, it's only to 1022f. I took some final temp readings and the outside dome top was 141f, the sides were 116f, the bottom of the slab was 162, with the hearth at 899 about six inches in front of the coals.

                            I let it cool some and tried cooking a couple of pizzas and the wife a calzone, it was too hot still but the pizzas did ok, the calzone burnt big time. Cleaned all the coals out and put door on, which I haven't insulated yet, the temp inside settled on 787. Tomorrow, I will see what it's holding and probably try some breads.

                            I bought a new IR thermometer off ebay so I could read dome temps higher than the 550f my old one will read.. I bought One of those Chines things they had for about $30, that was about as cheap of one I felt I wanted to try. I'm actually very surprised with it's accuracy reading the temps on the dome. Several times, just to compare it to the thermocouple, I took readings beside where the thermocouple comes through at and every time it was within a couple of degrees at to what the thermocouple was showing.
                            Last edited by BenKeith; 10-02-2017, 06:12 PM.

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                            • #15
                              This is what HOT looks like.

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