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Insulative Firebrick under FB board. - Forno Bravo Forum: The Wood-Fired Oven Community



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Insulative Firebrick under FB board.

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  • Insulative Firebrick under FB board.

    Hey guys this is my first post so HELLO! Got an idea, I have been researching all the different insulation materials (Super Isol, FB Board, Calcium Silicate Board, Vermiculite board etc.) available for installation under the medium (or low duty) firebrick floor and walls of my oven build.

    I had an idea: why not place an insulating fire brick layer down under the 2 inches of FB board? This would lift the FB board off the concrete hearth by 2.5 inches allowing for the board to be more sheltered from possible moisture infiltration and allow the insulative fire brick to take the brunt of any moisture that may be able to infiltrate between hearth and insulation layer. The added bonus would be the additional insulation provided by the insulating fire brick at a fairly low cost.

    The Fire Brick has a pretty high crush resistance: 1.5 Mpa (220 psi) and the FB is about .5 Mpa (72 psi)

    So here is what it would look like:

    Medium or Low Duty Cooking Floor
    2 inches FB Board
    2.5 inch thick Insulating Fire Brick
    Hearth Concrete

    Hmmm? Good idea, not not a good idea?

  • #2
    Re: Insulative Firebrick under FB board.

    Good idea I think.......... can't see why insulated bricks is a bad idea. The more insulation the better the oven works. How about cost?? I don't have any idea how much insulated bricks cost. However a mix of vermiculite/perlite and portland is still a very cheap and viable way to insulate the floor of an oven. My two cents................


    • #3
      Re: Insulative Firebrick under FB board.

      Other than the cost, there's nothing wrong with insulating firebrick. They are approximately equal to vermiculite concrete in insulation property, in other words, you'd want about four inches of them if you used nothing else.

      Putting them under refractory insulation board may not be their highest use; they're engineered to withstand extreme heat (they are used inside ceramic kilns) and the oven outside the insulation board hardly gets warm. I would think another inch of refractory board would be better and cheaper.

      Don't worry about the crushing strength of the insulation. They are all strong enough to withstand the pressure of the oven. As far as moisture, no insulation works well if it gets wet.
      My geodesic oven project: part 1, part 2


      • #4
        Re: Insulative Firebrick under FB board.

        I have 3" insulating firebrick sitting on a perlcrete base under my firebrick cooking floor (this is a mobile build). Now that I have used the oven enough and have driven out the moisture, it is holding the heat much better than it started out...in fact, I'm quite surprised how well. If I fire the oven up to pizza temps in the late afternoon/early evening, the floor is still 400 degrees at 7 the next morning. I don't know if it would be even hotter with insulation board under the floor, but the insulating firebrick seem to do a good job.


        • #5
          Re: Insulative Firebrick under FB board.

          Thanks for the information guys! Yeah the insulating brick would cost me approximately $250 for the floor of my oven. I have already purchased the FB board from Forno, I was just trying to think of another layer for it that would be more stout. Perlcrete is less expensive, just a little nervous about whipping that stuff up.


          • #6
            Re: Insulative Firebrick under FB board.

            I would just use perlcrete underneath, they're very easy to mix by hand and work with.


            My 34" WFO build

            Weber 22-OTG / Ugly Drum Smoker / 34" WFO