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Vent to Flue Transition Question - Forno Bravo Forum: The Wood-Fired Oven Community

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Vent to Flue Transition Question

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  • Vent to Flue Transition Question

    Hello Forum Members,

    Any thoughts on how much tapering with brick is needed between the rectangle of the vent and the round opening into the chimney? Can I just go from box to to pipe or do I need to create a funnel shape in mortar of metal?

    Also, do I need to insulate the arch or can I just insulate the dome?

    Thanks

  • #2
    Re: Vent to Flue Transition Question

    You'll get better draw on start up with a tapered transition between mouth and flue. A taller flue will help a lot too. If you don't mind a little smoke staining on the front of your oven, you can probably get by without either.

    Insulation around the arch helps keep heat in the dome, that area gets really hot and insulation reduces the amount of heat-leakage.
    My geodesic oven project: part 1, part 2

    Comment


    • #3
      Re: Vent to Flue Transition Question

      I don't mean to redirect this thread, but following up on your comment dmun, are you suggesting 4" insulating concrete (or a blanket) over the entry arch? I don't think I've seen that in many of the photos.

      Website: http://keithwiley.com
      WFO Webpage: http://keithwiley.com/brickPizzaOven.shtml
      Thread: http://www.fornobravo.com/forum/f21/...ttle-7878.html

      Comment


      • #4
        Re: Vent to Flue Transition Question

        I insulated my archway and my flue tile funnel, which in my case was very close to the dome. Partly this was because it was in an enclosure that I was dumping vermiculite concrete into anyway.

        Another factor was that I was building a reinforced concrete bridge to support my two story chimney, and I wanted something non-combustible to pour the slab onto.
        My geodesic oven project: part 1, part 2

        Comment


        • #5
          Re: Vent to Flue Transition Question

          Thanks for the insights. I am doing an igloo of stucco over the dome after I attach the 3 layer blanket of insulation.

          Comment


          • #6
            Re: Vent to Flue Transition Question

            I am hoping to do an igloo/stucco design myself (undecided on blanket vs. perlite cement insulation). I will be watching you closely. Please post photos and gathered wisdom!

            Website: http://keithwiley.com
            WFO Webpage: http://keithwiley.com/brickPizzaOven.shtml
            Thread: http://www.fornobravo.com/forum/f21/...ttle-7878.html

            Comment


            • #7
              Re: Vent to Flue Transition Question

              If it helps, here's what I did with my arched entry area and blanket.



              It's an inch blanket folded back on its self so I got a nice edge toward the decorative brick arch.
              My Build Thread

              Comment


              • #8
                Re: Vent to Flue Transition Question

                Originally posted by timo View Post
                If it helps, here's what I did with my arched entry area and blanket.



                It's an inch blanket folded back on its self so I got a nice edge toward the decorative brick arch.
                Greetings to a fellow Texan:

                I am looking at finishing like yours and ask how you keep the stucco render from cracking since it is laying on top of a compressable substrate? I am sure you put chicken wire or stucco lathe to re-enforce the stucco but am not sure what happens strenth wise if the stucco is compressed. (such as when a 9 yr old chucks his baseball against the stucco

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                • #9
                  Re: Vent to Flue Transition Question

                  I fastened chicken wire all around and anchored it. I applied a thick scratch coat, then a thinner coat, then a sponged final coat. I can stand on top of my stucco dome and it is solid. I haven't had the misfortune of having it kid tested, but there is still time and kids playing in the backyard...
                  My Build Thread

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                  • #10
                    Re: Vent to Flue Transition Question

                    For myself I used chicken wire over the blanket, it was much easier to fashion/form into a dome like shape than the usual stucco mesh and without all the joyful cuts one gets when working with stucco mesh. I then laid on a thick brown/scratch coat making sure to force the stucco mix underneath the chicken wire and then on top. Also a good suggestion is to sprinkle plastic fibers you get by the bag from the masonry supply folks into the stucco mixture. It has two benefits for the scratch coat, first it adds strength and the little hairs give the next coat something to bond to (it can't hurt).

                    I don't have pictures to show the steps, rain was forecast the next day I insulated and applied my first coat of stucco so I had to do it all in one day. I wanted the rain the following day to help cure the stucco since the summer here was exceptionally dry.

                    It's all worked out well. I endorse using blanket insulation. I bought 3 boxes for my oven and it was enough to cover it in four layers. I've had the oven over 950 degrees and the exterior of the dome is still at ambient air temperature.

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                    • #11
                      Re: Vent to Flue Transition Question

                      Originally posted by DimTex View Post
                      For myself I used chicken wire over the blanket, it was much easier to fashion/form into a dome like shape than the usual stucco mesh and without all the joyful cuts one gets when working with stucco mesh. I then laid on a thick brown/scratch coat making sure to force the stucco mix underneath the chicken wire and then on top. Also a good suggestion is to sprinkle plastic fibers you get by the bag from the masonry supply folks into the stucco mixture. It has two benefits for the scratch coat, first it adds strength and the little hairs give the next coat something to bond to (it can't hurt).

                      I don't have pictures to show the steps, rain was forecast the next day I insulated and applied my first coat of stucco so I had to do it all in one day. I wanted the rain the following day to help cure the stucco since the summer here was exceptionally dry.

                      It's all worked out well. I endorse using blanket insulation. I bought 3 boxes for my oven and it was enough to cover it in four layers. I've had the oven over 950 degrees and the exterior of the dome is still at ambient air temperature.
                      What stucco mix did you use? Looking at HDepot and Lowe's I don't see anything that stands out. Tons of different mortar and concrete mixes but nothing labled as 'Stucco'. Or is that a generic term for sand mix?

                      Comment


                      • #12
                        Re: Vent to Flue Transition Question

                        I bought mine from a masonry place (it might have said mortar mix) but I am pretty sure HD and Lowe's sell the branded products and on the racks under Stucco (Brown coat/Scratch coat) they have 90 lb bags of the stuff.

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                        • #13
                          Re: Vent to Flue Transition Question

                          What stucco mix did you use?
                          Quikrete Surface Bonding Cement along with the acrylic fortifier additive (to increase water resistance) have been highly recommended in the forum. I picked up some from HD this morning to apply to my igloo this weekend.

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                          • #14
                            Re: Vent to Flue Transition Question

                            What stucco mix did you use?
                            I used the quikrete Surface Bonding Cement over the oven and the block walls,, Great stuff and easy to work with...
                            1. If you want a smooth finish use a small trowel to finish (or a piece of insulation foam)
                            2. If you want a slightly rough finish after you trowel it on,, Go over it with a damp sponge
                            3. Add the acrylic fortifier for waterproofing
                            4. I also added color (terra cotta) If you do this mix only one bag at a time so your color comes out the same from bag to bag..
                            I have a 42 inch oven and used 2 bags to cover the dome to almost an inch thick
                            Mark

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