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A castable Barrel Oven with Refractory or Homebrew mix

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  • A castable Barrel Oven with Refractory or Homebrew mix

    Hello to all alternative oven makers,

    I have read quite a few threads on this forum and will continue to do so as I continue in learning more about oven building, pizza making and the dreaded bread baking.

    After reading various threads, I have decided to make a castable barrel oven.
    I have always seemed to be drawn to linear shapes and the barrel design is calling me out and of course based on my skill sets, I will be far more effective with making forms for the barrel method in creating a functional oven.

    Because of budget crunch, I have yet to decide on whether to purchase refractory cement (going back and forth on purchasing some 1-4 years old bags of castable cement from a distributor) or go the way of the homebrew:

    3 questions (with add-on's) to those who have been there:


    1) Homebrew: I have read of the famous 3:1:1:1 and some have suggested replacing portand with calcium aluminate and/or replacing the fireclay with grog and so on.

    I.Current thoughts on the “right” homebrew mix
    II.Is the mix by weight or volume

    2) What is the ideal dimensions for an effective oven (originally I was going to make a 36” igloo)
    I.Hearth width and length
    II.Wall height
    III.Back wall height and whether to be rounded or squared off
    IV.Center of Dome height

    3)Insulation: Because of cost restrain, I cannot budget for dreamy ceramic boards (way too expensive in New England)
    I thought of a cost effective solution by doubling down in combining an effective insulator (used under a concrete slab) for a heated floor to prevent the heat from seeping past the slab) and the recommended brick way of insulating (vermiculite).
    All material added on top of the support slab.


    I have more questions, but hopefully you can chime in with your thoughts on these.

    Best Regards,

    Sandro

  • #2
    Re: A castable Barrel Oven with Refractory or Homebrew mix

    The home brew mix is by volume not weight.
    Do not replace the Portland cement with calcium aluminate cement in the home brew mix. The lime in the mix acts as an accelerant when mixed with calcium aluminate cement and results in a mix that will go off faster than you can place it. You could eliminate the lime, but then you'll probably need to increase the calcium aluminate content which will make the mix a lot more expensive.

    The clay content in the home brew is important in making the mix workable. If you replace it with grog (fired, crushed clay) the mix will lose this workability somewhat.
    Also remember that the proprietary castable mixes usually contain fibres that burn out at low temp leaving a network of minute pipes for water vapour to escape through. If designing your own mix it is advisable to add polypropylene fibres.

    Vermicrete is a much cheaper alternative to calcium silicate insulating board, but it needs to have the water removed before it will insulate properly. I think it is better to dry it out as much as possible before building over it and locking the water in. With the cal sil board you don't have this problem.Whatever insulation you use it is best to place it under the floor bricks not under the concrete slab.

    Regarding the form of your oven, you can make it any shape you like if you are casting. If you're planning on cooking a lot of bread then a rectangular floor is more suited to loading than a circle. For pizza or roasting I can't see that there'd be much difference. A rectangular form will not heat as evenly as a dome and can have a tendency to having cool spots, certainly in kilns of this configuration anyway, usually in the corners. This could be either a disadvantage or an advantage depending how and what you are cooking.
    Last edited by david s; 01-24-2014, 03:25 PM.
    Kindled with zeal and fired with passion.

    Comment


    • #3
      Re: A castable Barrel Oven with Refractory or Homebrew mix

      David,

      I appreciate your recommendations. I will keep the Portland in (It is one of two items I have and will have plenty of by end of Feb.)
      [I]
      "If you replace it with grog (fired, crushed clay) the mix will lose this workability somewhat."
      If I use Grog will it make the mix stronger?, to minimize? cracks, If so, I can make small batches and vibrate teh form as I go to insure a densely packed form.

      I will add polypropylene fibres and the stainless steel needles to the mix ( I want this baby to last and shine: (my ego is at stake...no...hmmm > bragging rights... Yes! thats it)

      Vermiculite: So far I have found a 6 cu. ft. bag for $39 in MA. The nursery is a bit far from me, but so far the best price quoted for the amount.
      ---Has anyone in MA found a better price. I would prefer to buy in bulk and pick up. - Thanks


      "A rectangular form will not heat as evenly as a dome and can have a tendency to having cool spots"

      I whole heartily agree with you. One of the first articles I read on this site, was James's article on the effectiveness of rounded ovens (Why Italian Ovens are Round) but desire is one man's weakest points, right alone with lust but I digress.
      Thank you, as always
      Sandro

      PS: I finally saw your oven I have read so much about (it reminded of the little engine that could (outputting 60 + pizza in one outing out of that baby) reading the following thread: http://www.fornobravo.com/forum/43/b...-17285-12.html

      Why is it your oven does not have smoke all over the upper lip? entry when the flue is right on top of the entrance? I have seen many with similar designs with soothe all over the top.
      Last edited by Saovicente; 01-24-2014, 05:29 PM.

      Comment


      • #4
        Re: A castable Barrel Oven with Refractory or Homebrew mix

        I forgot to mention: It is #3 vermiculite 6 cu.ft. bag for $39.

        Also have anyone out in this small world of ours used the following 2 products:

        your thoughts:
        Attached Files

        Comment


        • #5
          Re: A castable Barrel Oven with Refractory or Homebrew mix

          Don't bother with poly fiber in your mix design, they will burn out.
          Old World Stone & Garden

          Current WFO build - Dry Stone Base & Gothic Vault

          When we build, let us think that we build for ever.
          John Ruskin

          Comment


          • #6
            Re: A castable Barrel Oven with Refractory or Homebrew mix

            Type S mortar is 2:1 - Portland/ Lime ratio 1800 psi. It's a building mortar for unit masonry and stonework.
            Old World Stone & Garden

            Current WFO build - Dry Stone Base & Gothic Vault

            When we build, let us think that we build for ever.
            John Ruskin

            Comment


            • #7
              Re: A castable Barrel Oven with Refractory or Homebrew mix

              Thanks Stonecutter,

              I appreciate your input. I have read that one would want type S because it has been hydrated. Do you have any recommendations on a particular lime product to use. In the Eastern part of MA, we have been overrun with the HD, Lowes, that it is becoming harder to find a smaller shop with a "othen than" item.

              Best regards,

              Sandro

              Comment


              • #8
                Re: A castable Barrel Oven with Refractory or Homebrew mix

                You want Type S hydrated Lime. Type S mortar is a different animal

                Look for a masonry supply yard...guaranteed they will have it, and with all the historic masonry restoration work in area, it should be no problem getting it.
                Old World Stone & Garden

                Current WFO build - Dry Stone Base & Gothic Vault

                When we build, let us think that we build for ever.
                John Ruskin

                Comment


                • #9
                  Re: A castable Barrel Oven with Refractory or Homebrew mix

                  Here you go, Greater Boston area, they carry Minute Man Lime....I used it many times when I lived in CT.

                  TLC Supply Cement
                  Old World Stone & Garden

                  Current WFO build - Dry Stone Base & Gothic Vault

                  When we build, let us think that we build for ever.
                  John Ruskin

                  Comment


                  • #10
                    Re: A castable Barrel Oven with Refractory or Homebrew mix

                    Originally posted by Saovicente View Post
                    David,

                    "If you replace it with grog (fired, crushed clay) the mix will lose this workability somewhat."[/I]
                    If I use Grog will it make the mix stronger?, to minimize? cracks,

                    PS: I finally saw your oven I have read so much about (it reminded of the little engine that could (outputting 60 + pizza in one outing out of that baby) reading the following thread: http://www.fornobravo.com/forum/43/b...-17285-12.html

                    Why is it your oven does not have smoke all over the upper lip? entry when the flue is right on top of the entrance? I have seen many with similar designs with soothe all over the top.
                    Replacing the clay with grog will do little to add strength. It would be considered a fine aggregate and will act similar to sand. unfired clay particle are much finer and theoretically are also a superfine aggregate so the mix would theoretically be stronger as a variety of aggregate size is stronger than a uniform one.

                    There are a couple of reasons my oven does not have lots of smoke staining on the front, in spite of the extremely shallow entry (the flue gallery is only 4" deep) 1. adequate flue pipe diameter and 2. a funnel like entry to the flue pipe.
                    Kindled with zeal and fired with passion.

                    Comment


                    • #11
                      Re: A castable Barrel Oven with Refractory or Homebrew mix

                      Originally posted by stonecutter View Post
                      Don't bother with poly fiber in your mix design, they will burn out.
                      Precisely, that's exactly what you want. Read #2
                      If you omit the fibres you run a greater risk of steam explosions and cracks. They are added not for reinforcement, the stainless steel needles do that.
                      Kindled with zeal and fired with passion.

                      Comment


                      • #12
                        Re: A castable Barrel Oven with Refractory or Homebrew mix

                        Originally posted by david s View Post
                        Precisely, that's exactly what you want. Read #2
                        If you omit the fibres you run a greater risk of steam explosions and cracks. They are added not for reinforcement, the stainless steel needles do that.
                        I did read that.

                        Networks of open capillaries may assist more steam to escape, but that also makes for a weaker casting, even with SS needles. There is nothing better than drying out the oven very slowly....after the material has cured. Explosions and cracking will happen with or without poly fiber, because of rapid firing, poor casting technique or drying the material before full strength is achieved.

                        Also, a porous material is a lot more susceptible to absorbing moisture into itself after it has been dried, and is going to be weaker than one that is dense during thermal cycling.

                        I respect your knowledge of casting ovens and refractory material, but I disagree with that logic and technique, because that practice creates weaker material and goes against what I know about masonry and strong castings.

                        EDIT: I have been reading different papers regarding the addition of PA fiber to refractory, and they support your point as to greater resistance]e to damage during the dry cycles. They also support what I am saying with regard to mechanical strength.

                        So I have to agree, David, after reading several research/engineering papers, that adding the poly fiber is a good idea for general home oven building. As with any mix design, there are things to consider...here is an excerpt from one of the papers...

                        Fiber reinforcement can offer advantages provided selection takes into account the following
                        factors:
                        • The fibers must have a minimum length to provide anchoring in the castable matrix.
                        • The unit volume and volumetric ratio of the fibers should be designed so that the distance
                        between them is compatible with the spatial scale of the mechanical loads to which the mate-
                        rial may be subjected.
                        • The mechanical strength and elasticity of the reinforcing particles (i.e., fibers) should be kept
                        within a suitable range at the temperature at which the stress is at its greatest (in the case of
                        castable drying, in the range 150–200°C, considering the surface temperature).

                        Another great point:

                        The correct design of the geometrical parameters of the polymeric fibers (length and diameter) is important in the optimization of the castable permeability after firing. Suitable selected
                        values of fiber length and diameter maximize the permeability level. This geometrical dependence is associated with the ability that the used fibers have to generate an efficient connection among the different regions of the castable structure.

                        For the short fibers (length <3 mm and diameter of 15 μm), despite their large number, the
                        length of the permeable paths is not sufficient to generate connections.

                        For the thicker fibers
                        (diameter >50 to 100 mm), the same effect is observed and is associated to the fewer fibers
                        per volume of castable.
                        Last edited by stonecutter; 01-24-2014, 08:46 PM.
                        Old World Stone & Garden

                        Current WFO build - Dry Stone Base & Gothic Vault

                        When we build, let us think that we build for ever.
                        John Ruskin

                        Comment


                        • #13
                          Re: A castable Barrel Oven with Refractory or Homebrew mix

                          As an aside, this is what I appreciate most about discussions like this. This one forced me to look into another aspect of refractory casting I had not considered to be of any value, and as a result, I will make a better cast oven in the future. Thanks David.
                          Old World Stone & Garden

                          Current WFO build - Dry Stone Base & Gothic Vault

                          When we build, let us think that we build for ever.
                          John Ruskin

                          Comment


                          • #14
                            Re: A castable Barrel Oven with Refractory or Homebrew mix

                            Originally posted by stonecutter View Post
                            I did read that.

                            Networks of open capillaries may assist more steam to escape, but that also makes for a weaker casting, even with SS needles. There is nothing better than drying out the oven very slowly....after the material has cured. Explosions and cracking will happen with or without poly fiber, because of rapid firing, poor casting technique or drying the material before full strength is achieved.

                            Also, a porous material is a lot more susceptible to absorbing moisture into itself after it has been dried, and is going to be weaker than one that is dense during thermal cycling.

                            I respect your knowledge of casting ovens and refractory material, but I disagree with that logic and technique, because that practice creates weaker material and goes against what I know about masonry and strong castings.

                            EDIT: I have been reading different papers regarding the addition of PA fiber to refractory, and they support your point as to greater resistance]e to damage during the dry cycles. They also support what I am saying with regard to mechanical strength.
                            The amount of fibres in the proprietary castable is minimal as they are not added for strength, so I would doubt mechanical strength would be effected. Presumably exhaustive testing has been done on the product and any loss of strength would be more than compensated for by the benefits the fibres provide in safer drying, otherwise they wouldn't add them to their product. Unfortunately the manufacturers keep their recipes secret so finding out the optimum quantity is not possible. Making your own castable mix is fraught with problems and is one reason I stick with proprietary product. But if I were making a one off for myself I'd be more than willing to risk a "try it and see" recipe which would certainly include polypropylene fibres
                            Kindled with zeal and fired with passion.

                            Comment


                            • #15
                              Re: A castable Barrel Oven with Refractory or Homebrew mix

                              Originally posted by stonecutter View Post

                              • The mechanical strength and elasticity of the reinforcing particles (i.e., fibers) should be kept
                              within a suitable range at the temperature at which the stress is at its greatest (in the case of
                              castable drying, in the range 150–200°C, considering the surface temperature).
                              In the case of the polypropylene fibres, as they are not added for strength this point is immaterial. In fact they melt at 160 C anyway. The stainless fibres do the strengthening instead and should be added to the mix at 2% min. by weight.
                              Kindled with zeal and fired with passion.

                              Comment

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