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Insulation - Rock salt and sand - Forno Bravo Forum: The Wood-Fired Oven Community

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Insulation - Rock salt and sand

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  • Insulation - Rock salt and sand

    I was talking with a spanish bulder/friend and he mentioned that before modern insulation materials like Arlita they used a mixture of sand (or crushed rock) and rock salt (gravel sized) for the insulating materials for their ovens.....interesting!

    I know there was some discussions about possibly using salt in constuction and found his reference worth mentioning here.

    Jim
    sigpicTiempo para guzarlos..... ...enjoy every sandwich!

  • #2
    Re: Insulation - Rock salt and sand

    Hello jim,
    Im confused about using sand. I have read others talking about using sand as an insulation, but to me it doesnt make sence. In my thinking insulation means air and lots of it, therefore the less weight per cubic foot the better the insulator right? The reason I am particularly interested is that when I built my oven I used 4" of sand under my firebricks with the intention of it functioning as a heat retention layer since its not much different weight wise per cubic foot (or meter in spain) as cement. If I have any problem with hearth temp its with it being to hot. I have 7" of depth in the dome and I have to mop the hearth a lot to stop pizza, bread or roasts from burning on the bottom.

    Sooooooooo, which is it, is sand an insulator or a heat sink.

    P.S. Jim when are you coming back to michigan? Let me know and Ill make sure to make plenty of dough for pizza's.

    P.P.S. its about 20 deg. here

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    • #3
      Re: Insulation - Rock salt and sand

      I think sand by itself would be a heat sink. My read in this discussion was that it filled the matrix between the larger salt gravel. So I think it was mainly salt and a little crushed stone to keep the whole mass solid.

      I do actually think that for this use they were building bread and roasting ovens so thermal mass would have been more important than insulation. (Did they even understand insulation 50 years ago? Seemed like we built stud houses with open air spaces right up to the 70's....)

      ....back in a week
      sigpicTiempo para guzarlos..... ...enjoy every sandwich!

      Comment


      • #4
        Re: Insulation - Rock salt and sand

        Air is not the only heat insulator, although it is a good one. Ultimately insulation ability has to do with heat transfer, and there is an engineering term that addresses this called K value. I looked the K value up for sand once - there is some variability as there are many types of sand. Sand is not abysmal as an insulator, but certainly not as good as the modern insulations suggested in the pompeii plans.

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        • #5
          Re: Insulation - Rock salt and sand

          Hello,
          As I know when you use salt, sand, glass or sand quartz in your cooking floor under firebricks is to add and extra thermal mass to your oven, it is less expensive that add other layer of firebricks and it is easy to work with it.
          I donít recommend you add salt; it is corrosive and degraded the floor and then the walls of the oven.
          If you want add an extra thermal mass at your cooking floor, the best choice is add 50% of glass and 50% of sand quartz you need to mix both; glass need to be grind like a sand.
          The other choice is add and extra layer of firebricks; from both options I donít know which is better to obtain better results.

          Saludos.

          Comment


          • #6
            Re: Insulation - Rock salt and sand

            Sand, salt and crushed glass are all materials that would leave air spaces between them, so while they are fairly heavy which creates more thermal mass, they will probably also act as an insulator to a certain extent.By contrast concrete has all the spaces between the sand filled with the fine cement leaving a denser material with no air spaces- a better conductor and more thermal mass to boot.
            Kindled with zeal and fired with passion.

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            • #7
              Re: Insulation - Rock salt and sand

              Also remember that "in the old days" they were not using the ovens occasionally, they used them every day. Under those conditions, it is not a bad thing if your insulation also has some thermal mass.

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              • #8
                Re: Insulation - Rock salt and sand

                Originally posted by david s View Post
                Sand, salt and crushed glass are all materials that would leave air spaces between them, so while they are fairly heavy which creates more thermal mass, they will probably also act as an insulator to a certain extent.By contrast concrete has all the spaces between the sand filled with the fine cement leaving a denser material with no air spaces- a better conductor and more thermal mass to boot.
                Hi David,
                You are right air between these materials is a poor insulator or a deficient thermal mass; if you use it as insulator you are going to have heat leak on your cooking floor to your earth, but if you use quartz sand and crushed glass like sand mixed in the same proportion it will work as thermal mass; glass and quartz are very good conductor heat, they canít be used as a insulator. If you donít believe me me, apply fire to these material and take a look that heat is distributes in a fast way into both materials.

                Saludos.

                Comment


                • #9
                  Re: Insulation - Rock salt and sand

                  Xabia Jim, what you wrote about your Spanish Builder coincides with what my Bolivian friend (60 yrs old) tells me as well. He recalls that his mum also cooked in a wood fired oven, and when they were build, salt was used as well below the finished floor level! By the way I am trying to get a pdf copy of the Pompeii oven, and the automated software allows for the American States only? Can someone please e-mail the latest copy? Thanking you in anticipation.

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                  • #10
                    Re: Insulation - Rock salt and sand

                    Once again,

                    Sand is not an insulator, neither is gravel, broken glass, rock salt or any other aggregate. Builders once may have used these things in ovens, but there is no excuse now for not using modern insulation.

                    All together now, the Forno Bravo Forum motto:

                    Insulate! Insulate! Insulate!
                    My geodesic oven project: part 1, part 2

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