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

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  • mongota
    replied
    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.

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  • Baza
    replied
    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

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  • mongota
    replied
    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.

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  • david s
    replied
    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.

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  • mrsrat
    replied
    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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  • mongota
    replied
    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

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  • Gulf
    replied
    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.

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

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  • mongota
    replied
    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.

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  • Gulf
    replied
    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.

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  • david s
    replied
    Originally posted by Gulf View Post
    Brad,

    Don't panic..You are in the same boat as 95% of this forum that did not include a moisture barrier or elevate the insulation.. Myself included . Though, I now (highly) recommend both. I also highly recommend a roof over the oven. If you do a roof over the oven, extend it out over the entry to allow yourself a dry work area. Aside from it calming your fears over a wet oven, it will greatly extend the number of days per year that your oven can be comfortably operated.
    A roof is the best solution to keeping your oven dry and if you do have one then waterproofing the exterior of the dome is unnecessary. This allows the dome to breathe. If the exterior is waterproofed moisture is also trapped in. We live in the tropics and after prolonged humid weather even if it hasnít rained the oven still picks up significant moisture making the exterior hot to touch. In that case not even a roof would prevent the moisture getting in.

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  • david s
    replied
    it is far easier to cast them in when laying the slab, but drilling up from the bottom will work.
    Last edited by david s; 07-27-2018, 09:32 PM. Reason: Typo

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  • brad mole
    replied
    great thanks for the reassurance guys!, i dont have weep holes as of yet but is it just a case of drilling from the log store underneath up into the slab until i just poke through into the calsil board in a few places? I think i will definitely build a canopy over the roof eventually and just keep it covered as much as i can until then

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  • Gulf
    replied
    Brad,

    Don't panic..You are in the same boat as 95% of this forum that did not include a moisture barrier or elevate the insulation.. Myself included . Though, I now (highly) recommend both. I also highly recommend a roof over the oven. If you do a roof over the oven, extend it out over the entry to allow yourself a dry work area. Aside from it calming your fears over a wet oven, it will greatly extend the number of days per year that your oven can be comfortably operated.

    Leave a comment:


  • UtahBeehiver
    replied
    I can't remember if you have weep holes in the hearth or not. If not, you can still drill a couple from the bottom side of the hearth so any water getting in can egress out. If water does migrate in, there is not permanent damage, it just the the CaSi will not perform well until dried out again (which is a pain in the #$%) but not the end of the world. You just have to do some drying fires to dry out the CaSi. By sealing the ends you do risk forming a basin for errant water to sit if you do not have weep holes.

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