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Preparing for steel oven build. - Forno Bravo Forum: The Wood-Fired Oven Community



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Preparing for steel oven build.

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  • Preparing for steel oven build.

    Hello Pizzaiolos,

    Long time lurker here. Finally getting ready to venture into the build stage.

    I have been assembling my materials for the better part of a year. This weekend I will take my angle grinder to a 40 inch propane tank end and cut off my dome. (Flushed it already, of course) I have a 4x6 dual axle trailer which I will be stripping down and having the frame built on. I scored a mess of firebricks on CL. Downside is I dont know their exact composition.

    I have been in contact with a local welding school that searches for build projects to train their students on. I have no welding experience myself, so I am hoping I can explain my needs to their instructors well enough.

    I have a couple of questions that I hope some of you can answer.

    For the support of the oven, I hope to have a square "basin" built into the frame, and I will layer 1/2 inch plywood, forno bravo 2 inch insulating board, then the fire bricks. Is this adequate? I would prefer not to cast a floor.

    Over the steel dome, can I get away with just forno bravo insulating blanket, then an outer shell? Or will it be terribly inefficient without a layer of thermal mass over the steel dome first?

    Of course I've read the major steel oven build threads on here already, and many thanks to those who have gone before. Cost is definitely one of my concerns as I only have 2k budgeted for the rest of the build. That includes the materials and having the student welders do their thing. Am I kidding myself that I can get it done for that?

  • #2
    Re: Preparing for steel oven build.


    I think you will need the thermal mass.

    Also, I have been communicating with another member in Texas who is building a similar WFO to what you are describing (save that he was not considering going without the thermal mass). He too was considering using a sheet of plywood as a base for the insulating board. I will give the same advice I offered to him and that is to consider using a thin sheet of steel instead, something like the steel forms which are used for elevated concrete floor pours. If those are unavailable then a reinforced sheet of 16 guage steel. Over the long haul of several years/decades the steel will be much more durable. If you were to have problems with the plywood the whole WFO would have to be disassembled.

    I would think you should have no problem building your WFO for 2 grand...I built my WFO (which is different in that it is on a platform) for about $500. So if you have the tank end, bricks and the trailer you should be fine. With the extra money I would consider an additional inch (or two) of insulating board beneath the hearth bricks.

    Hope this helps,


    • #3
      Re: Preparing for steel oven build.

      Thanks for your input. The steel vs plywood does make sense for long term durability, and likely wont add much to the pricetag.

      Regarding 4 inches of forno bravo board insulation under the hearth bricks. Does that board compress over time? Or will it remain at 4 inches for the long haul?


      • #4
        Re: Preparing for steel oven build.

        Trailer went over to the welders on Monday.

        Yesterday I placed my order for three sheets of Forno Bravo board...shipping sucks.

        Inside the steel dome, and on top of the fire bricks I want a 3cm thick hearth of either soapstone or more fire brick.

        I prefer a seamless 36.5 inch circle to fit inside my 37 inch dome.

        An Indiana soapstone manufacturer wants $650 to fabricate the circle, or will sell me a 40''X40'' square which I have to cut to my desired shape for close to $500.

        A Louisville refractory fire brick manufacturer said they can make me a same sized circle of firebrick for just over $300.

        I was hoping to get the soapstone but the cost difference has me leaning towards having the fire brick made.

        Any opinions?



        • #5
          Re: Preparing for steel oven build.

          Another thought...

          The plan I gave the welders was to create a 48"X48" tray to house the insulation board and bricks.

          The fire bricks I have are 4.875"X8.25" which means I would have to buy a saw to cut the bricks to fit that size. Not the end of the world, though I could just have him fabricate the tray a few inches longer to fit whole bricks.

          My math has it at 48.75"X49.5" for a 10X6 brick hearth

          Downside with that is that the 3 sheets of 24"X36" FB board would leave me with a little gap around the edges. Could I fill that gap with sand?


          • #6
            Re: Preparing for steel oven build.

            Back from the welders today with the first part of the project.

            First, a couple of pics of the trailer.

            Last edited by scarnucci; 10-01-2011, 12:22 PM. Reason: photo fix


            • #7
              Re: Preparing for steel oven build.

              Here I have installed the FB board. The boards were not quite equal in size. One was a bit wider than 24"" and one was just under. Took a little trimming to fit into the 48" wide tray.

              One FB board was also a little thicker than the others, so it is a bit uneven. Not the end of the world.

              Ive got most of the bricks in, I'll have to cut one row. Wondering if I should stagger the whole thing or if I can just keep them as is. Dont have a brick saw, and am wondering if I should attack them with an angle grinder or bite the bullet and buy the saw.

              Here is a reference on how the steel dome will fit. Dome is still at fabricators so this is a piece of extra that I threw onto just to have a look see.

              When the dome is finished, this is where the oven door will be. I'm going to have to have a shelf made, because the door "tunnel" is going to extend out farther than this tray is right now.

              Plan is to weld three thin metal bars from the dome at 90* to each other, left, back and right, and attach it to the frame. I am weighing the fact that they may act as heat sinks, heating up the frame, against the fact that the dome slid all over the trailer when I was driving it to the welder's shop. I need to have something keeping it in place, and it being on the road occasionally, I cant put all my faith in weight and gravity doing it all.

              Dome should be done next week sometime.


              • #8
                Re: Preparing for steel oven build.

                The bricks cut like butter with a diamond disc on a cheapo Harbor Freight grinder. I bought one of the grinders for my WFO just to see how long it would last and because I didn't want to pass any more brick dust thru my Makita than I really had to. The grinders as so very inexpensive I figured they could not be built well enough to last long. Well the Harbor Freight grinder is still going strong, it's just as loose and noisy as when I first started it but it does what is asked of it. Diamond disc also came from Harbor Freight. Just remember the dust mask and eye protection and hearing protection... the bricks cut easily but not quietly.

                A suggestion on your construction...Cut the interior bricks to fit inside the dome; however, the ones on the bottom should not extend all the way to the edge of the tray. Allow them to extend out so that they support the steel dome and the cladding but fill the rest of the space with vermicrete or perlcreate. This is to stop the outer bricks (beyond the cladding) from acting as heat sinks pulling heat from the oven.

                Regarding the steel support bars for keeping the dome in place: I would suggest you think something along the lines of bars with holes drilled in them to lessen the x-section and thus heat transmission.

                Have you given any thought to some triangulation/bracing on the support legs for the oven?

                Otherwise looking good!



                • #9
                  Re: Preparing for steel oven build.

                  In looking at the pictures, I am wondering why the bottom brick layer covers the whole pan. If this is for thermal mass, I would only have the brick layers under the oven footprint itself.

                  The way you now have it, the lower brick layer will "wick" heat away.

                  With your design, you could both isolate and contain the finished oven and brickwork with a layer of verimcrete up to the top of the pan.

                  When you cut the brick, either with a saw or grinder, keep the dust down and extend the life of your cutting edge by soaking the bricks first.
                  Last edited by Neil2; 10-01-2011, 10:22 AM.


                  • #10
                    Re: Preparing for steel oven build.

                    Thanks for your responses.

                    So, I'll cut back on some of the brick layer, and fill in with vermicrete.

                    If I wanted to sink 3 anchors in the vermicrete layer, and weld the support bars to the anchors, would the vermicrete have enough strength to hold the anchors in place?


                    • #11
                      Re: Preparing for steel oven build.

                      If that was my set up I'd be including some gussets or diagonal bracing on the stand legs that attach to the trailer chassis.
                      Kindled with zeal and fired with passion.


                      • #12
                        Re: Preparing for steel oven build.

                        Regarding the strength of the vermicrete: terrible in tension, better than terrible in compression but not much better. One could get really complex in designing so you have little or no heat loss in your hold downs/anchors.

                        Realistically (IMHO) what you want is something that will keep everything together when you are forced to do a panic stop. You most likely will be driving conservatively otherwise and so therein lies the grey area between what is enough and what is not.

                        An idea:

                        A plate of steel welded to the steel dome at each end of where the underneath supporting cross member is located. This plate is maybe something like six inches long by three inches wide and maybe 1/4 inch thick. It is welded horizontally up from the bottom of the dome where it will eventually be embedded in vermicrete. This small plate has a one inch hole drilled in it. The hole is located in the plate so that it will not be embedded in the thermal mass when the plate is welded to the dome. Thru this hole there will be a 3/8ths inch bolt which is welded to the tray support so the threaded end is upright. This bolt will be long enough so that when assembled it sticks up thru the hole in the plate by an inch (minimum). Locate the steel dome when assembling the oven so the bolt passes thru the hole but doesn't touch it. Once the dome is set upon the bottom bricks and before you pour the vermicrete thread a large nut onto the bolt. This nut can be constructed of a large fender washer welded to a regular nut, the idea is to make it so that the bolt cannot come thru the hole when attached yet the interstitial space between the bolt and nut assembly and the small plate is filled with vermicrete. Thus you have the thermal break and yet the dome is less likely to part company with the trailer when you (hopefully never) have to make a panic stop. The bolt should be a grade five...no need springing for the extra cost of a grade eight as when you weld it the heat treating will be lost and grade fives are basically grade eights without heat treatment. The weak point is the weld between the bolt and the support but hopefully some of the energy will be taken up by the compression of the vermicrete in the hole before the load is transmitted to the bolt, bending the bolt before transmitting enough energy to break the weld.

                        Just my thoughts and first thoughts at that. No liability as to failure, take it as worth what you paid for it...which is nada.

                        Hope this helps,

                        Also, when I grind anything that makes a lot of dust I always try to set up my large shop vac so that the intake is where the grinder will be throwing the waste. Helps a lot to keep the dust from going everywhere.


                        • #13
                          Re: Preparing for steel oven build.

                          Thank you for your comments and suggestions for welding the dome in place.

                          I cut some bricks today and picked up the dome from the fabricators.

                          Some pics of where I am at:

                          Bricks are not locked down yet, obviously. The 2X4s are in place where a vermicrete mix will go. I'll probably end up welding some bolts in the middle of that area and then some plates from the bolts to the dome, as per some suggested.

                          More or less where I want the dome at.

                          I stopped by a local refractory fire brick factory on my way from picking up the dome. Talked to them about layering the dome in two inches of refractory cement, then insulating it. He is also into pizza and pizza ovens and suggested that the refractory be on the interior of the dome. As this is mobile, I dont really want that. He doubted the effectiveness of any refractory on the outside of the dome, and suggested that I just insulate the hell out of what I have. That the insulation and shape of the dome will keep blasting the heat downwards towards the brick floor which will absorb and hold the heat.

                          So, I am considering building 4 walls up from the existing frame, and making a square enclosure for the dome. Wrap the dome in 607 super wool, then fill in the remainder of the area inside the enclosure with vermiculite. Wall it off, roof it, call it done.

                          Is there any chance at getting away without the refractory?


                          • #14
                            Re: Preparing for steel oven build.

                            "Is there any chance at getting away without the refractory?"

                            Little to none IMHO especially if you expect to produce pizzas commercially (ie: lots of pizzas baked one after another sort of rapidly). But no one here has tried it so if you decide it is worth the experiment let us know how it works out.

                            Looks good! I would suggest that you wire wheel (large cup brush on angle grinder) the inside of the dome. My WFO has had no problem with rust flaking down on what's baking inside but if one rubs one's hand on the interior surface one does come way with a red brown colored hand. I wire wheeled the interior (exterior as well, didn't want problems with paint burning off) of the steel dome when I built mine and have had no need to further address internal rust issues. It's a dirty task but IMHO worth doing.



                            • #15
                              Re: Preparing for steel oven build.

                              Does the vermicrete border need to be of a refractory cement or will regular quick-crete work? I did pick up 3 bags of refractory, but at $30 a pop I wonder if the job will be done just as well with $5 bags.