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Ever have a terra cotta flue liner crack? - Forno Bravo Forum: The Wood-Fired Oven Community



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Ever have a terra cotta flue liner crack?

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  • Ever have a terra cotta flue liner crack?

    I did.

    Last weekend, My brother heard a loud "Pop" while the fire was burning. The next day, there was a vertical crack on the flue liner, all the way from the bottom to the top. Luckily, it is located in the back of the oven, so it can't be seen.

    I attribute it to the fact that the very HOT fire we were burning was burning soot, and perhaps the soot in the chimney caught fire.

    At any rate, I patched it with furnace cement, and it's perfectly OK. I've fired the oven twice since then.
    There is nothing quite so satisfying as drinking a cold beer, while tending a hot fire, in an oven that you built yourself, and making the best pizza that your friends have ever had.

  • #2
    flue tile crack

    The flue tiles are refractory material, just like firebricks. They are not supposed to crack, and when they do, it's because they are cemented to common masonry that expands at a different rate.

    Chimney cleaners talk about cracked liners, so I guess it must happen.
    My geodesic oven project: part 1, part 2


    • #3
      Enclosing Flue Liner


      Are you planningon enclosing your flue liner with any insulation and/or decorative housing? You could seal your crack with your handing fireplace caulk, then wrap/hide the liner.

      Pizza Ovens
      Outdoor Fireplaces


      • #4
        Re: Ever have a terra cotta flue liner crack?

        The upper section of my two-section flue liner cracked yesterday just before my second pizza party. I had a roaring fire inside that began shooting flames up into the flue.

        It was a thin crack, running from top to bottom. The upper liner is bonded to the liner below with refractory mortar, and it not attached to anything else. As far as I can tell, the lower liner is intact.

        I have metal studs surrounding the flue, waiting for hardibacker and stucco. Should I replace the inexpensive liner section? I could cut it out with a diamond saw and put a new one on. I'm slightly worried that I'll either crack the lower liner, or break the mortar bond of the lower liner to the vent arch.

        I could also go get some furnace caulk, if I knew where to find it. I bet the caulk is more expensive than the liner!

        Would refractory mortar work if I mixed it nice and thin?

        Should I just fill the chimney enclosure with perlite and forget about it?
        I'm building a Pompeii Oven in Austin, Texas. See my progress at:
        Il Forno Fumoso


        • #5
          Re: Ever have a terra cotta flue liner crack?

          What is a flue liner for....?

          It prevents noxious gases from escaping to indoor areass and prevents fires from starting in nearby materials (like wood stud walls). I would guess that in many outdoor wood fired ovens there is little chance of either of these issues being a problem.

          If it's part of an occupied structure, I'd evaluate it a little more....but a crack is not a big problem with a masonry oven....you will probably have them!

          Forget it, or patch it and be happy!

          my 2 cents
          sigpicTiempo para guzarlos..... ...enjoy every sandwich!


          • #6
            Re: Ever have a terra cotta flue liner crack?

            Ah, yes! My pumice precast flue liner cracked vertically, too after the second 1200 dgree flame feat (out the top of the chimney).

            The mortar joint on the top section broke clean, and when I went to take it off it cracked in my hands. I went to buy replacement liners, and re mortared it back on to the second section to make my three feet.

            As I gazed upward into the chimney from the bottom to see my mortar job, I noticed the long crack all the way up from vent to top of chimney.

            so far, the cracks are only on the inside of the liner-I see nothing on the outside. I'm going to forget about it and build my brick facade around it (leaveing the air gap, of course).

            Moving on!


            • #7
              Re: Ever have a terra cotta flue liner crack?

              Ours cracked in the pattern of a spider web. I attribute it to the fact that I enclosed the first two inches in mortar, thereby not allowing expansion. As other's have said, as long as it doesn't collapse, what is the difference? Cook on!

              Album: http://picasaweb.google.com/fornososo/Pizza#


              • #8
                Re: Ever have a terra cotta flue liner crack?

                So what is the workaround for ceramic flue liners that crack? Is it possible to attach the base of the liner without mortaring it in so it can expand as needed?


                • #9
                  Re: Ever have a terra cotta flue liner crack?

                  I think the solution is to have a perfectly level base and to only use an eighth inch layer of adhesive flue mortar to attach. Yea Right!

                  Edit: I actually have no idea how to keep it from cracking. It amazes me that they can stack these things all the way up a masonry chimney with no lateral supports along the way.

                  Last edited by DaveW; 06-11-2010, 07:14 AM.
                  Album: http://picasaweb.google.com/fornososo/Pizza#