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Using Refractory Mortar to skin Vermicrete dome - Forno Bravo Forum: The Wood-Fired Oven Community

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Using Refractory Mortar to skin Vermicrete dome

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  • Using Refractory Mortar to skin Vermicrete dome

    I know this is not ideal and may be a silly question, but I'm looking to see if its possible to use Refractory Mortar (purchased from Forno Bravo) to apply a skin to the inside of a vermicrete dome that I just completed.
    The only Refractory Cement I can find local is Rutlan, which seems to have mixed reviews when applied with a trowel (seems to need a form). I have a lot of Mortar so wanted to check and see if that would work in place of cement for a skin.

    If not, Alternatively, can the mortar mix be modified to make it more suitable to use as a skin? (I also have SS Needles if that helps)

  • #2
    I would expect any skin coat applied to the inside of the dome to fail

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    • #3
      I'm afraid that Toomulla is right. Also, the needles may work in a full thick cast dome. But, I would be afraid of them in a parge coat. If the parge with needles fails, they could end up in your food .

      EDIT: Just wondering if this oven is another victim of the infamous medicine ball vermiculite/perlite video?
      Last edited by Gulf; 05-22-2018, 03:21 PM.
      joe watson

      "A year from now, you will wish that you had started today "

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      • #4
        Here is a link to an answer to a similar question a few weeks ago. I did not want to say it but I totally agree with the advice that was given.
        joe watson

        "A year from now, you will wish that you had started today "

        My Build
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        • #5
          Apart from a resulting thin layer being likely to fail the substrate it is applied to, in this case vermicrete, needs to be a bit moist or water in the applied layer will be sucked out leaving insufficient for the hydration process. Also if the substrate is too wet it will interfere with achieving a good bond. So not dry, but not too wet. Give it a try weíd be interested to hear how you go.
          Kindled with zeal and fired with passion.

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          • #6
            Thanks for the feedback and insights. Given feedback that thin layer will likely fail I plan on using a mold to do a refractory casing (mixed with SS needles) that's thicker. Will report back on how it goes

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            • #7
              Just wanted to update everyone on results. Below was the process I used to build my oven, which Ive been using all summer long with great results:

              - Vermicrete dome over exercise ball, roughly 4 inches (allowed to dry for a week with wet blankets)
              - Flipped it over them applied a coat of castable refractory cement to the inside of the dome (approximately 1 inch thick)
              - Placed it on table built with wood, topped with stone pavers, then insulation, then firebrick (it was heavy to carry and flip, but not too bad)
              - Coated the outside of the dome with refractory mortar, covering the firebrick and insulating base
              - Applied 2 inches of insulation with chicken wire
              - Coated with scratch and base coat of stucco
              - Last Step: will coat with final layer of acrylic stucco

              As mentioned, I've used it now about 12 times and its functioned flawlessly. It takes about 5 medium logs and 45 mins to get up to temp then burns
              very efficiently. I'll post additional images
              Last edited by desmodici; 08-20-2018, 07:56 PM.

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              • #8

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                • #9
                  Looks GREAT desmodici ! Where did you get that smokestack? I like it!

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                  • #10
                    Originally posted by bentedesco View Post
                    Looks GREAT desmodici ! Where did you get that smokestack? I like it!
                    Looks like a Dura-tech Stainless cap (8DT-VC) and pipe.
                    Mongo

                    My Build: Mongo's 42" CT Build

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                    • #11
                      Thatís correct. Itís a Duratech double walled 6 inch diameter 24 lencgth pipe with a chimney cap, both bought from forno bravo. Love the look of it as well and functions flawlessly. Iíll take a few more pics tomorrow and update the thread.

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                      • #12
                        A few more of the build along the way

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                        • #13
                          More build pics

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                          • #14
                            Nice job. Iíd be most interested in how your oven will stand the test of time. Can you report back in a years time? The two big drawbacks of a vermicrete dome are lack of strength and thermal mass. However, just as with boat design itís all a matter of compromises, what you gain on the swing you lose on the roundabout.
                            Kindled with zeal and fired with passion.

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                            • #15
                              well said David, I approached the build with that in mind, a compromise between "the perfect oven" and reality of my restrictions and requirements. Given HOA restrictions, space in my yard, close neighbors etc., I wasn't able to pull off my dream build of a conventional brick oven. I also wanted to do something with minimal effort/cost to test the waters and ensure this is something I would use frequently, wouldn't put out too much smoke given the close proximity of neighbors, etc. E.g. I was initially going to go with cement base but switched to wood after I realized 1) how many bags of cement i would have to haul/mix and 2) how much effort would be required if I had to tear it down for some reason. I'm very happy I went the wood route as it simplified things greatly. Entire build which included a lot of drying time took less than 3 weeks of intermittent work, mostly on the weekends.

                              So far my major concern of smoke bothering the neighbors is not an issue. It produces minimal smoke while getting the first few logs going but once it hits 300 internal temp its completely smokeless.

                              I will definitely report back frequently and if I experience any issues. I use it about once per week so will get some good testing on the design etc.

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