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Chimney flue problem

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  • Chimney flue problem

    Am a newer member am in the middle of building a dome style oven and have been using a lot of info from this great site and feel the need to bring this up.....hope this does not offend anybody but am seeing what I consider a common mistake and that is the use of metal flues ... to build an authentic pizza oven and then put a cheap metal flue liner that will only last a few years needs to be addressed... use clay flue liners or thimbles instead.. easier and lasts as long as the oven.

    Having said that metal liners can be replaced / relined they do it to old fire place chimneys all the time with metal tubes usually after having a chimney fire that has cracked the masonry flue and surround.

    FWIW the Heat Stop mortar is far superior to the tub type castable refractory as far as ease of use .

    When using any type of mortar/concrete no matter what application always and I mean always use pressure when applying to surface such as buttering brick or pouring a slab.. I spread a thin layer of mud (mortar) with pressure on surfaces that meet. Poured concrete that is not floated with pressure will not be as strong as just you don’t believe me just put a shovelful in a shallow pan with out using pressure repeat in another pan with pressure.
    Pressure creates a proper bond when laying brick/block and when pouring slabs or footings it brings the butter to the top and helps eliminate air and pockets.
    This is also why you wet/soak brick including previous course if it is dry....usually pull the brick out several min before using too wet is not good either and if it’s hot out and in the sun use shade to keep it from drying out too fast (this will make for a bad bond)

    I am not a mason by trade these are tips my father who was a master mason passed on to me hopefully they will help someone else as well.

    It would be nice if you had what appears to be European style trowel with round tip , easier to use when backfilling joints..might find one in a large masonry store where they sell tools for swimming pools or hot using standard pointed trowels myself.

    Am not trying to sound like a know it all, these are all time proven tips that will make for a better job.
    I am Mike from NE Georgia and am about half way thru the dome taking my time with the oven as it is part of an overall landscape plan with lots of stone work to go ..
    will try and post pictures when done hopefully by late spring
    Good luck with y’alls projects.

  • #2
    Mike, I totally agree with all you said , with the reservation on the clay liners, they need expansion room around them and tend to crack in intense heat or if they are exposed . I used on edge red brick from the oven up then a fabricated steel chimney 8 gauge , 7”x 23” ,, volume rather than velocity.. works great , no soot on my outside arch 500 cycles on!


    • #3
      If the pipe is normal steel it will corrode very quicklly, especially because it’s thin.Any galvanised coating will be destroyed if it gets hot enough and the fumes given off are quite toxic. That is really old fashioned and these days 304 stainless steel is used pretty much universally. It does not corrode and will last a lifetime. Places at the beach may get a bit of surface rusting on 304 and if really concerned go for 316 (double cost), but my flue manufacturer told me in 30 years he’s never had a complaint about 304 flues needing replacement and the jump to 316 is unwarranted. The stainless colour will change to a pewter appearance where it gets hot, but it won’t corrode. Other alternatives are thick boiler tube or perhaps a copper pipe.
      Last edited by david s; 03-21-2019, 01:54 PM.
      Kindled with zeal and fired with passion.


      • #4
        Both good points .... have seen heavy steel pipe used effectively in a couple of wood stove installs...I cut a radius in two fire bricks same as thimble and use as collars to seat against the bottom of the thimble and throat of chimney and lay a brick chimney around thimble and fill void with perlite....sometimes sand / vermiculite dirt clay or mixture was used to temper the heat around the thimble/flues they would be subject to.
        Am using a perlite and Portland mix to lay refractory brick and fill between them and as 2+ plastered layer on outside ot dome.
        it will have a stone veneer to match surrounding masonry with a roof and voids between dome and outer masonry walls will be back filled with perlite not sure how much is gained by it at this point but its not much more work to do it and cost is fairly low.
        Thanks for your replies am looking forward to enjoying this style of cooking and entertaining.


        • #5
          Mike , the loose perlite ( I used block fill = vermiculite) to fill the space will settle a bit over a few heat cycles .. I left my vent cap unfinished and topped it up after a month or so of weekly ( and more) firings . As I live in a cold climate I have over 10” of poured in insulation over the dome blanket.


          • #6
            Your right about the settling but this point the fill on top is really over kill at least in this milder climate ...I also would not use vermiculite as it is used primarily to retain water when used in soil mixtures unless you can be sure it won’t take on moisture. Have poured many bags of it in concrete block walls as a kid But anyway that is why I chose perlite over vermiculite. Also when laying the rock veneer at the base of the stone I will leave out part of the joints so to let any moisture drain thru, these are usually referred to as “weep holes”.
            thanks for the input


            • #7
              Mike, I have not had any moisture issues with a metal roof and 10” thick fieldstone walls but look at what I found this morning for an early April fools day ... 30cm of fresh snow with an few hours of rain in the middle ! No words...


              • #8
                It’s a good looking oven...I don’t envy the snow , things are blooming here and I am slowly getting the dome and flue built looks like a couple more bags of Heat Stop are needed and then the expensive pallets of flag stone.. ouch.
                Cant wait to light the first small curing fire just to see how it works
                Stay warm