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Help with insulating concrete layer, please, we're freaking out alittle - Forno Bravo Forum: The Wood-Fired Oven Community

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Help with insulating concrete layer, please, we're freaking out alittle

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  • Help with insulating concrete layer, please, we're freaking out alittle

    Hi,

    Yesterday we poured the insulating concrete layer for the 42" Tuscan-style we're building. We used 5:1 Vermiculite:Portland, and the guys actually mixing and tamping the concrete are experienced in all kinds of concrete installation, but had never before worked with this mixture.

    The cat walked on it in 2-6 hours after we poured it and left 1" depressions all over it. Weird.

    The concern is that it will never cure to the point where it will properly support the weight of the oven.

    Your advice on this will be greatly appreciated!
    Cheryl & Gary

  • #2
    Re: Help with insulating concrete layer, please, we're freaking out alittle

    Been there, done that... its wierd stuff to work with and doesn't act anything like regular cement. Sometimes it firms up in a day or two, but mine took about a week...

    So if the cat still leaves dents in it by this time next week, you're allowed to worry. In the meantime just leave it where it is, it'll be fine.

    Oh, and so's you know what to expect, the finished product feels a bit like cork, but it really is strong enough to support an oven.
    "Building a Brick oven is the most fun anyone can have by themselves." (Terry Pratchett... slightly amended)

    http://www.fornobravo.com/forum/f8/p...pics-2610.html
    http://www.fornobravo.com/forum/f9/p...nues-2991.html

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    • #3
      Re: Help with insulating concrete layer, please, we're freaking out alittle

      Thanks! That helps!

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      • #4
        Re: Help with insulating concrete layer, please, we're freaking out alittle

        Let it cure and I expect that you will be OK. I mixed my insulating layer at a 9/10 to 1 ratio and it poured like pudding (just be sure that the poured layer is all pudding not vermiculite floating upon water). Next day it was firm and yet the surface was delicate and pieces could easily be dislodged by rubbing with a finger tip. A day or two after that and it was like cork; yes, it still could be point loaded and compressed but bricks spread the load out over a much larger area. One real advantage of pouring the mix quite wet is the pour is almost completely self leveling, just a quick screed and you're good to go.
        Hope this is some re-assurance, just give it some time to cure. Oh and if you haven't already, I would fill in the cat prints :-)
        Bests,

        Wiley

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        • #5
          Re: Help with insulating concrete layer, please, we're freaking out alittle

          I had cat prints in my support slab. I bet s/he was in for a rude shock at paw licking time.

          To your question, it takes a week, dries to cork like consistency, and has lots of compressive strength, but will easily chip away at the edges.
          My geodesic oven project: part 1, part 2

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          • #6
            Re: Help with insulating concrete layer, please, we're freaking out alittle

            Keep it damp for at least a week . If it drys out at all then it won't set properly and you may have to start over.

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            • #7
              Re: Help with insulating concrete layer, please, we're freaking out alittle

              Thank you all so much for the reassurance and advice!

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