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Insulation bricks - Forno Bravo Forum: The Wood-Fired Oven Community



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Insulation bricks

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  • Insulation bricks

    Hi I am planning on building a pizza oven soon. Can you use insulation bricks under the fire bricks in the Hearth. I live in Thailand and am having difficulty finding vermiculite or Perlite, Isol, Laowool, Insulfrax etc... I have located firebricks, morter and industrial insulation bricks. I have read that Pumice may be used as an alternative. Has anyone tried this?

  • #2
    Light weight, porous bricks should help to insulate.


    "Can you use insulation bricks under the fire bricks in the Hearth."

    (M) I know nothing about the insulating properties of pumice but I'm sure that if you used the lightest weight, most porous bricks you could find that they would help to keep the refractory heavy hearth brick floor heat from wicking into the supporting hearth slab.

    (M) I pasted the blurb below from the original Forno Bravo plans located at:


    (M) Remember to adjust the height of your block stand to accomodate any change in floor height from what you hope to realize as a working height for your oven opening.

    Insulating fire brick
    . These light-weight refractory bricks are designed to stop heat, and as such have low conduction and low heating holding capacity. They are often used to insulate industrial equipment. A typical insulating fire brick weighs about 2 lbs, compared with an 8 lb light duty fire brick.
    "Everything should be made as simple as possible, ...
    but no simpler!" (Albert Einstein)


    • #3
      insulating bricks

      Insulating bricks would make a wonderful insulation layer under and around an oven. One 3 inch layer on the inside of a ceramic kiln allows the inside of the kiln to heat up to red to orange heat, while only a couple of hundred degrees on the outside. The reason they are not used for this is that they are very expensive and have to be cut to fit the dome like the inside bricks.

      If you can't get vermiculite or pearlite, volcanic pumice should work fine. It's what the ancient romans used, after all.
      My geodesic oven project: part 1, part 2


      • #4
        Thanks guys looking fwd to making some high temp NY style pizza. I've got just the spot for an oven in my back yard!! I have a few other projects on the go but as soon as I tidy them up it will be jumping into igloo ovens.


        • #5
          Insulating fire bricks.

          A guy at a special effects company offered me a bunch of these. I figured I had no use for them. They are still sitting in his warehouse.


          • #6
            He shoots, he scores


            That's it. That could be your scrounged under oven insulating layer. I have never done research into the efficiency of insulating firebrick, though I can ask around and can find out more.

            If they are free, you can stack up a couple of layers of those under your oven.

            I have always though of insulating firebricks and regular firebricks pumped full of air. They are made of the same basic refractories (alumina and silica) are a regular firebrick, so they can withstand the stand high temperature, but then rather than absorbing heat, the air holes block it. An insulating firebrick weighs a fraction of a regular low or medium duty firebrick.

            Beammeup -- if you can't find insulating firebricks, or they are really expensive, pumice is a good alternative. If you really strike out, you can always use sand. We don't recommend it, but if it's your only choice, it will work in a pinch.

            Last edited by james; 10-03-2006, 01:58 AM.
            Pizza Ovens
            Outdoor Fireplaces


            • #7
              The really good insulating bricks/tiles are found at NASA - get a load of of the castoffs. "Jewelers no longer have to worry about inhaling dangerous asbestos
              fibers from the blocks they use as soldering bases. Space Shuttle
              heat-shield tiles offer jewelers a safer soldering base with
              temperature resistance far beyond the 1,400 degrees Fahrenheit
              generated by the jeweler's torch."

              They used to be made by Rockwell but have been bought by Vought Aircraft Ind.


              • #8
                found some

                I have found some vermiculite in Thailand, at a horticulture place. They sell it for around $35.00 for 4 cu ft. Is that expensive? How many bags for a 38" igloo oven at 4" for base and cover? I have also contacted a chap in Northern Thailand who made an oven. He used slowly burned rice hulls, or husks. He says they make a great insulation. They use that here for brick making kilns. I think I would prefer to use the Vermiculite if this price isnt too outragiuos.


                • #9
                  loose fill

                  I used 6 of the 4 cu ft bags of perlite for my 42" oven at 6" thickness. If you take a lot of time to close dead space in your oven you can reduce your amount to use. Perlite bags were $15 for 4 cu ft where I live, vermiculite was about $20. I bet you can use 4 bags, maybe less. One note on loose fill, close any gaps, no matter how tiny. Drake used the canned self expanding foam - a brilliant idea that I wish I had considered.


                  • #10
                    vermiculite & prosper...

                    Hi there,

                    I'm still studying the basics of this arcane craft, and am collecting prices from Australian suppliers. One firm has a materials list for a 100 cm round pizza oven and states you'll need three bags of vermiculite at $26.60 ea. plus 1 bag of ciment fondu at $40 for insulating this oven. It doesn't sound much, does it - the quantity, I mean. Perhaps they refer to the hearth part only?


                    "I started out with nothing, and I've still got most of it"


                    • #11
                      One of the things that I find interesting about brick ovens is the range of options that exist that could be called a "brick oven", or "wood-fired oven". You can literally stack up a bunch of bricks, or pour clay or concrete around a form, fire it and cook bread and pizza. Cro Magnon man had wood fired ovens. At the other end of the spectrum you choose oven chambers specifically designed for baking Italian pizza and surround them with very efficient space-age insulators. And there are many points in between. You can install an oven on a 6" non-insulated concrete slab, and it will cook.

                      The good part of this is that as a builder, you can pick where you want to be on the spectrum -- based on how much effort you want to put into it, money, how often you will use it, etc.

                      Clearly, a well-insulated oven made using a specially built oven chamber (shameless plug for Forno Bravo), will cook a lot better -- and as the chef, you will enjoy using it a lot more. It will heat up fast, it will hold heat better, it will hold high heat better, it will use less wood -- so that you can make great Italian pizza (or NY, or Sicilian), and bake bread and roast a turkey without the oven giving up on you. If you are a real pizza lover, you need a high-end oven.

                      Can you install a modular oven with one page of refractory mortar and three bags of Vermiculite? Yes. But if you can try a little harder, you will be well rewarded. If you can't, having a less sophisticated oven is a lot better than not having an oven.
                      Pizza Ovens
                      Outdoor Fireplaces


                      • #12
                        bricks again

                        I got the price for the insolation bricks, 80 cents apiece, they are white-ish and 9"x4.5"x3". I think I might go with these for the base with say an inch or 2" of vermiculite between the Insol bricks and the fire bricks. The fireclay bricks are also 80 cents and they only have med duty. I understand medium bricks will get hotter, so would it be wise to increase the insulation? Any suggestions for the size of the base? I would like to build a 36" or 38" oven
                        Thanks again


                        • #13

                          The insolation bricks are composed of 15%-Alumina, 51%-Silica, 29% Lime and 0.5% Iron Oxide. with a thermal conductivity of .16 W/m.K at 800 deg C. Does this mean anything to anyone? I would like to know if this would be better than vermiculite for my base or if I should just go with the vermiculite. The cost of the bricks seems reasonable.


                          • #14
                            I will ask my thermal engineer contact -- the one with the simulation software. I'm not sure how fast he will back, but I'll ask.
                            Pizza Ovens
                            Outdoor Fireplaces


                            • #15
                              thermal conductivity

                              Vermiculite concrete, per a previous post here by Jengineer has a thermal conductivity of 0.69-0.73. Super isol at 750F has a thermal conductivity of 0.55. Lower is better. If the insulation bricks are affordable then go for it. The K value for insulating fire bricks stays fairly flat through the usual temperature range of a pizza oven (there's a graph here http://www.ibar.com.br/index_eng.html). Their insulating firebricks have thermal conductivity values of 0.2-0.25 for low density and 0.4 for higher density brick but their units are kcal/m h C, multiply your bricks' K by 1.163 to convert ( http://www.engineeringtoolbox.com/un...ter-d_185.html ).

                              The same source Jengineer used for the thermal conductivity of vemiculite concrete lists perlite concrete as having a thermal conductivity of 0.58 ( http://www.schundler.com/perlcon.htm ). Strangely enough, dry sand has a lower K value, 0.35, although if it absorbs lots of moisture it is worse than concrete (which has K value of 0.9-2) going up to 2.7.

                              I'm happy with my oven's thermal performance for home use with just perlite concrete under the bricks - I have never been able to feel heat through the concrete support under the perlite concrete and my oven gets hot and stays hot for making pizza and bread. I have 3 inches of perlite concrete. I don't see any reason you would need to place insulating bricks over a layer of vermiculite concrete.