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High Medium & Low Fire Brick Data - Forno Bravo Forum: The Wood-Fired Oven Community

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High Medium & Low Fire Brick Data

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  • High Medium & Low Fire Brick Data

    4 Basic Fire Brick Ratings (Super-Duty, High, Medium & Low Duty).

    High & Low duty bricks are more readily available since there are more applications for them in the field.

    Low duty bricks are best for traditional fireplaces where temperatures do not get that high since it is a mostly open design. They are not optimum for pizza ovens since temperatures may exceed there limitations and crack which would be a total bummer after investing all the time and cost of building a home made oven from scratch! If you are purchasing new bricks, get the correct duty (see below).

    High Duty Bricks are used in heavy industry where temperatures get very high since the furnaces are tightly closed and the process demands these extreme temperatures. As a side note, these bricks are more difficult to cut and may get too hot for cooking pizza. (They will certainly last a long time)

    Super Duty which is for really high heat applications and not a consideration for pizza.

    Medium Duty bricks with an approximate silica content of 50% and alumina content of 35% are what Forno Bravo recommend. I assume since food cooking ovens (Pompeii etc) are semi closed, and experience temperatures higher than fire places but lower than industrial furnaces, a medium duty brick is recommended.

    Mt Savage FireBrick in Frostburg Maryland produces a Medium Duty Firebrick (see attached Data Sheet) with a 59.9% silica content & a 32.9% Alumina content.

    This is slightly different than the percentages specified by Forno Bravo (9.9% difference in silica & 2.1% difference in alumina) I wonder if these differences have a better or worse impact on pizza quality or if anyone knows of a manufacturer with percentages closer to what Forno Bravo recommends.....

    Mt savage also has a HIGH duty firebrick that has a 34.5% alumina & 58.9% silica content which seems to be close to the recommended sweet spot Forno Bravo recommends which they to refer as their MEDIUM Duty with a slightly higher Alumina content at 38%?????? There is also something referred to as a super-duty which is not even a consideration. Seems the porosity is higher.....
    Attached Files
    Last edited by gsanto; 06-24-2013, 08:11 AM.

  • #2
    Re: High Medium & Low Fire Brick Data

    Low duty bricks are best for traditional fireplaces where temperatures do not get that high since it is a mostly open design. They are not optimum for pizza ovens since temperatures may exceed there limitations and crack which would be a total bummer after investing all the time and cost of building a home made oven from scratch! If you are purchasing new bricks, get the correct duty (see below). If you already have low duty bricks, proceed at your own risk weighing the advantages of saving money against the risk of bricks that do not last.
    Hundreds of ovens, including mine, have been built with low duty firebricks. Our ovens rarely exceed 1000 degrees f, which is well within the ratings for these bricks. Our Australian friends, who contend with high cost firebricks, regularly build ovens with "pressed reds", with only incidental silica content, with apparently good results.

    When you start dealing with medium and high duty bricks, you start dealing with refractory dealers, with specialty pricing, and a reluctance to deal with amateurs.
    My geodesic oven project: part 1, part 2

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    • #3
      Re: High Medium & Low Fire Brick Data

      I do not believe there are any standards in the firebrick industry. The terms low, medium, and high are generally used by the uninformed lay persons (like us oven builders).
      Anyone that is into refractories knows these are generalized terms and the alumina content can vary by 10% from one manufacturer to another. A product data sheet tells it all. Stick with an alumina content in the mid 20% to mid 30% range and you are golden. As for low duty (which I used and have been perfectly happy), I have never seen any with less than 21% and have never seen any rated at less than 1700 F - well within what is needed for a WFO. I went with the cheapest available low duty, rated at 2300 F and I believe have a 23 or 24% alumina content. Cost was 77 cents each at a brickyard. The refractory specialist wanted over $2.50 each for what we would call medium duty, I think they were 38 or 39% and rated for over 3000 F. Overkill and over priced if you ask me.

      RT

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      • #4
        Re: High Medium & Low Fire Brick Data

        Originally posted by RTflorida View Post
        The terms low, medium, and high are generally used by the uninformed lay persons RT
        I thought it referred to the wear duty of the brick, light duty is a soft brick, medium duty is a medium duty brick, and high duty is a hard brick capable of taking some punishment.
        Last edited by brickie in oz; 06-10-2011, 01:06 AM.
        The English language was invented by people who couldnt spell.

        My Build.

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        • #5
          Re: High Medium & Low Fire Brick Data

          brickie, that may be true. The so called experts that I talked with told me that industries are concerned with the specifics - the chemical composition, continuous heat rating, thermal expansion rates, etc. The generalized terms low, medium, and high are just that - generalized, and can include a farely broad spectrum of compositions.
          Since I'm not in the industry, I had to trust what they told me and the information contained on the data sheets.
          I guess I should have just voiced my disagreement with the statement concerning low duty - "they are not optimal for pizza ovens since temperatures may exceed their limitations and crack"
          Totally untrue in my opinion, the data from the manufacturer will support that. Since low duty (fireplace bricks in the US) are readily available and considerably cheaper, it makes perfect sense to use them in our case.
          Maybe in a commercial setting a higher wear rating may be desirable to avoid periodic hearth brick replacement, then again, health departments frown upon all of the joints in a brick hearth and require larger tiles or a continuous slabe for the hearth.

          RT

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          • #6
            Re: High Medium & Low Fire Brick Data

            Low duty are fine for ovens, personal kilns, and general purpose use. It is an abrasion rating more than a temp rating anyway. High duty refractory is used for things like cement kilns where you have tons of highly abrasive material literally rolling around inside them for years at very high temps.

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            • #7
              Re: High Medium & Low Fire Brick Data

              Originally posted by RTflorida View Post
              "they are not optimal for pizza ovens since temperatures may exceed their limitations and crack"
              RT
              Everyones an expert on things they know nothing about.

              I get told constantly by house owner "experts" on the correct way of laying bricks.
              The English language was invented by people who couldnt spell.

              My Build.

              Books.

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              • #8
                Re: High Medium & Low Fire Brick Data

                All it takes is one "expert" to throw things into a tizzy. There is such a wealth of information just on this forum about what works and what doesn't, it amazes me that there are so many questions, misconceptions, and half truths floating around.
                I've said it before, do your homework and your build will go fine. This forum proves there are 1001 ways to skin a cat, and in brickie's case, roast it in the WFO

                RT

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                • #9
                  Re: High Medium & Low Fire Brick Data

                  Well its good to know that many are happy with low duty bricks. Why is it that Forno Bravo recommends medium duty??? Like they say, I would like to "Enjoy the process" and want to make sure I pick the very best brick for my oven....

                  Comment


                  • #10
                    Re: High Medium & Low Fire Brick Data

                    i'm confused. i understand that high-duty bricks can withstand higher temps, but how or why would they get any hotter than the low or medium duty bricks with the same oven fire? and if they truly get 'too hot' why are they being used in professional bread ovens?

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                    • #11
                      Re: High Medium & Low Fire Brick Data

                      Read the posts above, the rating is all about resistance to abrasion.

                      Heat in = heat out, it cant get any simpler than that.
                      The English language was invented by people who couldnt spell.

                      My Build.

                      Books.

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                      • #12
                        Re: High Medium & Low Fire Brick Data

                        Originally posted by brickie in oz View Post
                        Read the posts above, the rating is all about resistance to abrasion.

                        Heat in = heat out, it cant get any simpler than that.
                        oddly enough, i did read the above posts which is why i am asking in the first place....

                        "High duty fire brick. These brick have very high alumina content, get very hot (1500F and up) and are designed for continual high-heat applications, such as furnaces. They are expensive, and will get too hot for some of your oven uses, such as baking bread and roasting. In general, pizza wants heat between 750F and 900F, while bread and roasts cooks best between 500F and 600F. (Note that brick ovens are able to cook at higher temperatures without burning because of the moist heat inside the oven and shorter cooking times.)"

                        from the forno bravo brick primer
                        Last edited by tngabe; 10-31-2011, 09:13 PM.

                        Comment


                        • #13
                          Re: High Medium & Low Fire Brick Data

                          Originally posted by tngabe View Post

                          "High duty fire brick. These brick have very high alumina content, get very hot (1500F and up) and are designed for continual high-heat applications, such as furnaces. They are expensive, and will get too hot for some of your oven uses, such as baking bread and roasting. In general, pizza wants heat between 750F and 900F, while bread and roasts cooks best between 500F and 600F. (Note that brick ovens are able to cook at higher temperatures without burning because of the moist heat inside the oven and shorter cooking times.)"
                          No material can get hotter than the energy put into it, it goes against all physics.
                          If you come across some you will be a $Gazillionaire instantly.
                          The English language was invented by people who couldnt spell.

                          My Build.

                          Books.

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                          • #14
                            Re: High Medium & Low Fire Brick Data

                            that's what i was thinking, but didn't want to question the infalliable forno bravo!

                            looks like i'll be getting some 12x12 high duties!

                            Comment


                            • #15
                              Re: High Medium & Low Fire Brick Data

                              The higher duty bricks are capable of withstanding greater thermal shock. In the case of a WFO the temp reached is not particularly high, but the rate of increase is. It is this fast temp rise that does the damage.
                              Kindled with zeal and fired with passion.

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