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Building 42 in Pompeii, any pearls regarding laying down 2 in FB BOARD beneath firebr

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  • #16
    I also agree that an oven needs to breathe. Used in normal construction, brick and stucco are supposed to be porous. However, they are meant to be exterior walls, not roofing material. I think that we can waterproof them for our application as long as we give the oven another "lung" from which to breathe .
    Last edited by Gulf; 07-28-2018, 06:08 AM.
    Joe Watson " A year from now, you will wish that you had started today" My Build Album / My Build

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    • #17
      Agree. There are "waterproofing solutions" that are vapor permeable and vapor impermeable.

      i just did a second coat of Thoroseal on my dome. The Thoroseal will shed liquid moisture, but will allow moisture vapor to pass through it. In essence, it'll minimize liquid water getting in to the structure, but when a fire is lit, it'll allow any excess moisture vapor to escape.

      Id never recommend coating a shell with something vapor impermeable like RedGard.

      Any of these ovens that are designed to be permanent will benefit from a roof overhead. The most carefully constructed shell can still suffer from a thermal crack. Or a freeze/thaw crack in winter.
      Mongo

      My Build: Mongo's 42" CT Stone Dome Build

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      • #18
        Are they any alternatives to CalSil in this design? Why not use perlite since it has better thermal retention?

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        • #19
          Do you mean “better insulative”? If so the answer is no. It takes about twice the thickness of a 5 to 1 perlite to Portland cement ratio to equal CalSil.
          Joe Watson " A year from now, you will wish that you had started today" My Build Album / My Build

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          • #20
            Originally posted by rwiegand View Post
            Lay down 4"?

            No one seems to suggest putting a vapor barrier between the board and the concrete. Since water can wick through the concrete and reach your insulation, depending on the enclosure design, that would seem to be a simple precaution. I don't know why it's not done. I didn't think about it in time or I would have put down a sheet of stainless steel under the insulation to create a barrier.
            I was in the "concerned" group, so I used RedGard on my slab. Once the RG was cured and the 4" thickness of insulation was down on top of it, I painted the edges of the insulation with RedGard as well. A couple of photos here:

            https://community.fornobravo.com/for...410#post392410

            Mongo

            My Build: Mongo's 42" CT Stone Dome Build

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            • #21
              I didn’t even think about moisture. I have a roof over my oven, and I am building my oven on top of a 5/8” steel plate with a 4.5” layer of perlite/cement mix right now. I’m wondering if before I put the brick floor down if I should coat my perlite with the RedGuard as I live in Houston and it’s very humid.

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              • #22
                If you seal the perlcrete how can the moisture escape? As the steel is impermeable you should probably drill some holes in it to allow passage of moisture. Not sure how Redguard will stand up to heat.
                Kindled with zeal and fired with passion.

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                • #23
                  Originally posted by mrsrat View Post
                  I’m wondering if before I put the brick floor down if I should coat my perlite with the RedGuard as I live in Houston and it’s very humid.
                  Agree with David. If you put RedGard over your perlite and placed the firebricks on top of the RedGard, the high oven temps would destroy the RedGard in no time at all. I have RedGard on the slab, underneath my 4" of board insulation. If I recall correctly, the highest temperature I ever recorded at that point was 98F.
                  Mongo

                  My Build: Mongo's 42" CT Stone Dome Build

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                  • #24
                    Great conversation on the insulation and water management - I know Mongota had a disaster he had to dry out - posted on his thread!
                    Utah saved my butt when I poured the hearth - I forgot to drill holes in it to let water through - and when posting my progress, he reminded me!! Thank goodness!
                    I put a layer of bathroom tile under the CalSi board to lift it up and let water egress ... so far so good.
                    Mine is enclosed and waterproofed from the outside - but provided a lot of ventilation at the roof line (ridge vent and side vents) - I think that should help.

                    I wish I had put 4" of board underneath - I followed the original build plans and didn't have access to more board at the time of the build and have 2".
                    It works - but I am wondering about floor temps dipping as I make pizzas.

                    Barry
                    You are welcome to visit my build HERE

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                    • #25
                      Originally posted by Baza View Post
                      I know Mongota had a disaster he had to dry out - posted on his thread!

                      Barry
                      Ah, memories. Good times, good times. Not! lol
                      Yes, we had to move across country to take care of ailing in-laws. My oven (which only had the brick dome built) sat unattended for almost two years (and subsequently two New England winters) under tarps and plastic sheeting. The cover abraded and allowed water in. My 4" of board insulation was saturated. Took some long fires to dry it out, but it's been dry as can be ever since.

                      Mongo

                      My Build: Mongo's 42" CT Stone Dome Build

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