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Hardibacker to level floor bricks? Fireclay vs refractory mortar - Forno Bravo Forum: The Wood-Fired Oven Community

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I'm Peter Reinhart! Ask Me Anything! Monday, February 15, 2016 7:00-8:00 pm EST

To kick off our AMA feature, we have invited author, chef and master bread maker and host of Pizza Quest, Peter Reinhart, to be our first host! Peter will be in the Forum on Monday, February 15th, from 7:00 - 8:00 pm EST. If you are unable to be online during the live session, you can post your questions in the sticky post. Peter will answer those questions during the live session on February 15th. You can view Peter's answers to your questions as well as what happened during the live session in the session thread.

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You will notice a new forum at the top of the main page called, "Ask Me Anything". This forum will be used for live one hour "Ask Me Anything" (AMA) sessions hosted by people who are knowledgeable in different areas pertaining to wood fired ovens. How it works:
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Hardibacker to level floor bricks? Fireclay vs refractory mortar

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  • Hardibacker to level floor bricks? Fireclay vs refractory mortar

    My firebricks are ordered and will be dropped next week and I have two questions I need answered prior to building:

    1: I have an 8" layer of vermiculite/concrete for the insullating layer. I must have mixed it with too much vermiculite and it turned out fairly crumbly but has finally set. My problem is it has created plenty of voids and a non level surface. Since I have sufficient insulation can I use a layer of Hardibacker board under the floor bricks to level everything out? ie - what temps do we see under the floor and can the Hardibacker plank withstand them?

    2: I am a bit confused with the terms 'fireclay' vs refractory mortar. Fireclay seems to be just that.A 'clay' with a high alumina and silica content. Refractory morter adds sand and cement to the mix? My vendor is sending me 3 gallons of fireclay which he says may be used directly to mortar my bricks. The website for the product states it has a chemical composition that is almost identical to Heatstop 50, and water may be added to thin the product. So do I add sand to this in a 1:1 ratio and go or use it straight from the container?

    Hope everyone had a great 4th.

  • #2
    Re: Hardibacker to level floor bricks? Fireclay vs refractory mortar

    I don't know about the answer to your second question but I do know the answer to your first. And that is no. I made a proto type door for my WFO out of Hardibacker and at temperatures 450 F and above it starts to give off a very obnoxious smell. It also loses what strength it has becoming fragile. The fragile part is not a problem as you are wanting it strictly for leveling if I'm reading your post correctly, but the obnoxious smell no one would want near food.

    Hope this helps,
    Wiley

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    • #3
      Re: Hardibacker to level floor bricks? Fireclay vs refractory mortar

      I am a bit confused with the terms 'fireclay' vs refractory mortar. Fireclay seems to be just that.A 'clay' with a high alumina and silica content.
      This is correct.
      Refractory mortar adds sand and cement to the mix?
      The homemade mixture does. Professional mortars like refmix and heatstop are quite a bit more complicated.
      My vendor is sending me 3 gallons of fireclay which he says may be used directly to mortar my bricks.
      Gallons? Huh? I've never heard of fireclay sold premixed with water.
      The website for the product states it has a chemical composition that is almost identical to Heatstop 50
      Then it isn't fireclay. It's a premixed wet refractory mortar. We've never heard about anything but problems with these wet products. They take forever to set up, and they don't produce a hard waterproof seam. It's probably OK for leveling your floor, since you can also do that with dry refractory mortar mix, but I wouldn't build your dome with the stuff.

      This is what fireclay looks like:



      It's cheap and should be locally available, from mason or pottery suppliers.

      It's mixed with sand to prevent it from cracking. You can use it to mortar your firebricks, as Frances did. It never vitrifies, but if you keep it dry it works fine.
      My geodesic oven project: part 1, part 2

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