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    Still searching the archives, but hoping someone might have a quick answer: Tore out an old patio here at the house. I have a whole lot of used brick. it is about half red clay brick and about half a yellow brick - it seems harder and perhaps denser and most definitely looks like refractory brick. Is there a test for whether I might have refractory brick?

  • #2
    Amusinglisa,

    Welcome to the forum, Yes, clay fire brick will be heavier than most other clay brick. But, I came across some pavers the other day that fooled me. I went to a local brick yard last week looking for a deal on some fill brick for a project. In that area of the yard they had a pallet and a half of what looked like 4"X8" firebrick. When I questioned them they told me that they were pavers. It turns out that they were pavers made by Pine Hall Brick called Courtyard Buff. I bought a few and fired a couple in my oven to dome clearing temp. They passed that test. So, I went back and bought the rest @ fill brick price.

    You can do a similar test on them by firing them in a bed of charcoal. (Lump charcoal is better because it burns hotter) That is not a test for firebrick. It is just a test to see if they will hold up. Can you add some pics of the yellow brick that you have? Include any markings on the brick if any.


    Joe Watson " A year from now, you will wish that you had started today" My Build Album / My Build

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    • #3
      I don't see a mark on the bricks, but they have fewer holes in the other bricks (I think I attached the photo at least once...)
      Attached Files

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      • #4
        OK, Next question: Worst case scenario -- if they do OK with charcoal (lighting a fire now) but they are not refractory, what might break-down be? 100 +/- uses? Fewer?
        thanks!!

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        • #5
          I share your desire to repurpose used materials. But, if you will allow me to share my regret after buying and using recycled firebricks, I would not do it again! Cleaning mortar from those bricks turned out to be a big, big job. The few dollars I saved was overshadowed by the extra work required to clean and recut the bricks so they had good edges for my use. HTH
          Lee B.
          DFW area, Texas, USA

          If you are thinking about building a brick oven, my advice is Here.

          I try to learn from my mistakes, and from yours when you give me a heads up.

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          • #6
            If the bricks have holes in them they are unsuitable because the holes reduce their density and will act as insulation. You need solid bricks. Yellow bricks are more likely to be more suitable because they contain less iron oxide (red) which tends to be a no no for firebrick composition because of its fluxing effect.
            Kindled with zeal and fired with passion.

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            • #7
              Originally posted by Lburou View Post
              I share your desire to repurpose used materials. But, if you will allow me to share my regret after buying and using recycled firebricks, I would not do it again! Cleaning mortar from those bricks turned out to be a big, big job. The few dollars I saved was overshadowed by the extra work required to clean and recut the bricks so they had good edges for my use. HTH

              AHA! There have been a few incidences of poor choices involving my male offspring. I have about 300 clean, stacked bricks. =) Meanest mom in the world...

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              • #8
                My best guess is that they are also pavers. They do make 4"X8" firebrick. But, they would have been too expensive to use as pavers unless they were salvaged. If they were salvaged, and being that large a number of brick, they came out of a kiln of some type. Some would wonder what type of kiln?

                There are several ovens on this forum that are built out of clay pavers. Maybe one of the southern hemisphere builders can answer your question about how long they might last. Firebrick are extremely expensive down there. So many of them use clay pavers as their only option. I'm using the brick that I mentioned earlier in a chimney.
                Joe Watson " A year from now, you will wish that you had started today" My Build Album / My Build

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                • #9
                  What you're looking for in Gulf's charcoal test is splitting & cracking mostly. It may be just a few flakes that pop off the side or an actual brick breaker. Red clay bricks produced 40-50 years ago were fired at a higher temp than today's standard bricks and are much more "heat stable". The newer bricks just don't generally take the big temp swing very well. That said-again as Gulf pointed out-several southern hemisphere members on the forum have used newer red bricks/pavers with success...still depends on how well they were made at the factory. That's what the charcoal test helps you determine. Repeated rapid heating (firings), time, and weathering will generally cause spalling in lower density standard bricks. Again, it depends on the firing time and materials used in the brick's production. As to how long a "good" brick will last is difficult to answer...WFOs in Pompeii certainly have lasted plenty long enough but I'm sure they were created with better materials and higher firing temps than standard building brick. It seems like there should be some test that we could apply that would be easy and accurate...maybe somebody on the forum will have more input here.

                  I noticed in your pictures that all the bricks looked to be the same size. My experience (much more limited than some others on the forum) is that firebricks tend to be visibly larger (9"x4.5") than regular bricks (8"x4"). But as Gulf said, he did find some that were 8x4, The refractory/firebricks also are normally quite a bit heavier/denser. I just weighed a firebrick and it was a little over 7 pounds (3.2 Kg) while the solid red brick was a little over 5 pounds (2.4 Kg). I also noted that the surface texture of the firebrick is pretty consistent...no little air pockets and pits. In the red brick there are quite a few of these surface blemishes and pits...like the bricks in your pictures.

                  As Lee (Lburou) above noted, cleaning recycled bricks with old mortar attached is a pain and not generally a good value when you throw in your labor ...but having the kids do the work makes them an exceptional value (even though you temporarily earn the "Meanest Mom" award).

                  Hope this helps a bit...
                  Mike Stansbury - The Traveling Loafer
                  Roseburg, Oregon

                  FB Forum: The Dragonfly Den build thread
                  Available only if you're logged in = FB Photo Albums-Select media tab on profile
                  Blog: http://thetravelingloafer.blogspot.com/

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                  • #10
                    Wow! Thank you, Gulf, David, Mike and Lee! The hamsters are running and I believe some thinking is beginning. We are starting our base and will consider/contemplate the oven brick - we are simultaneously doing a roast and have some bricks in the charcoal there. These bricks are all minimally 40 years old - I spoke with the original homeowner's daughter -- SHE remembers banging mortar off of them as well. =D

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                    • #11
                      OTOH, I suppose I could throw a few in my kiln at 1200*F and see what happens...

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                      • #12
                        The temperature a brick is fired to initially may not be a suitable indicator of its thermal shock characteristics. eg low fired coarse clay bodies have better thermal shock characteristics than earthenware or stoneware fired bodies that are fired to their mature temperatures. The evidence for this is the low fired pots used in South America for cooking. Clay bodies fired to porcelain temperatures do have better thermal shock characteristics, but at that temperature 1300 C + only porcelain clays will handle heat. The composition of the clay is a far more important factor than the temperature it has been fired to and unfortunately without complex testing you'll never know its composition. The proportion of alumina to silica is one of those that are more important, alumina being more refractory. Fluxes in the clay also play an important role. The sudden heating and cooling that we subject our ovens to (300 C+) is way in excess of any safe recommended pottery firing schedule. But firing a brick up to around 1000 C (WFO temps will top out at around 550C at tops) really quickly might be a better test.
                        Kindled with zeal and fired with passion.

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                        • #13
                          The heat cycle in your kiln would need to be accomplished hundreds of times to get the final answer about the heat tempered personality of those bricks....
                          Lee B.
                          DFW area, Texas, USA

                          If you are thinking about building a brick oven, my advice is Here.

                          I try to learn from my mistakes, and from yours when you give me a heads up.

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