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What is Grog - Forno Bravo Forum: The Wood-Fired Oven Community


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Dome Installation Video - Casa / Premio / Modena


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What is Grog

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  • What is Grog

    I am finished assembling our Le Panyol 66 oven and the instructions for grog over the dome before insulating. I suspect grog is some form of crushed fire-brick but have no idea where I can acquire something like this in Seattle. Any ideas?

  • #2
    Re: What is Grog

    Grog is fired, crushed clay.There are all kinds and different screen sizes. Ask your local refractory supplier, or try pottery suppliers.Grog is a way of adding clay to a mix without having to deal with problems of shrinkage (it's preshrunk) and the tendency of it to want to turn back into mud when wet.

    In Australia we also call any alcoholic drinks "grog".
    Don't the instructions provide any more information? If not contact your supplier.
    Last edited by david s; 11-12-2011, 12:32 AM.
    Kindled with zeal and fired with passion.


    • #3
      Re: What is Grog

      Thank you David! I found crushed fireclay at a foundry supply company in Seattle for only $6 per 50lb bag. We also refer to 'grog' as an alcoholic beverage.


      • #4
        Re: What is Grog

        Grog is actually crushed firebricks. Usually and mostly made by crushing all the unsaleble/reject bricks. In some situations it is made by just extruding and firing rough shaped bricks for this specific purpose. Made in various particle sizes and graded through screens, and then packed in various sized bags.


        • #5
          Re: What is Grog

          Crushed firebrick, not fireclay for this application. For brick in general it is crushed fired clay. It is also water with rum in it.


          • #6
            Re: What is Grog

            Thank you for the clarification. Is there a typical source for crushed fire brick, such as a refractory supply company?


            • #7
              Re: What is Grog

              Most refractory yards will have this product. Use a medium to corse grade.


              • #8
                Re: What is Grog

                There is a big difference between grog and fireclay. Yes the clay is ok for your poormans mortar.


                • #9
                  Re: What is Grog

                  Fire clay has been fired but not to the point of vitrification. It can more accurately have been said to be dried very well, then ground fine. Once clay has become vitrified, it does not matter how fine it is ground it is not clay.

                  As stated, the purpose of grog in brick making (or refractory plaster) is to provide an aggregate that will not shrink under heat. In brick plants, brick that are rejected after firing are crushed as filler (grog), while brick that are rejected before firing are re-ground and added back as clay (part of the clay body that will be vitrified in the kiln).


                  • #10
                    Re: What is Grog

                    [QUOTE=Tscarborough;123562]Fire clay has been fired but not to the point of vitrification. It can more accurately have been said to be dried very well, then ground fine. Once clay has become vitrified, it does not matter how fine it is ground it is not clay.

                    It is still clay no matter how high it has been fired. The clay under goes a physical change when it reaches 573 C called quartz inversion. Above this temp the clay becomes permanent. ie. wont turn back into mud. Grog is sintered. ie. taken to at least 900 C, at much higher temps the fired clay would be extremely hard to crush and for most uses it is more desirable for the grog to be porous rather than vitrified. The purpose of firing the clay and then crushing it is to prevent the shrinkage of wet clay and its tendency to return to mud.
                    Last edited by david s; 11-15-2011, 01:55 AM. Reason: grammar clean up
                    Kindled with zeal and fired with passion.


                    • #11
                      Re: What is Grog

                      Yes, I should have said plastic.