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  • UtahBeehiver
    replied
    Heed Gulf's and Dave's advise. Water has a way to sneak in no matter what you do, even on fully enclosed ovens or even during the curing process. A "vent" on the dome will prevent build of pressure caused by water converting to steam. Since you only have a scratch coat on you can still put in a vent at the apex of the dome Dave's vent is in his vent stack. I would be concerned about using Tyvek in "between" stucco layers and still getting a good bond between the stucco brown and finish coat.

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  • david s
    replied
    No, the blanket doesn't swell when wet, but it can hold a lot of water. It dries out ok too. At least they're the characteristics of the stuff I use (Morgan super wool), there are plenty of others.

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  • johnnybrewmeister
    replied
    Thanks for the info Gulf. Since a Tyvek sheet passes water vapor, I would think there would be no build up of pressure.

    Does CF blanket swell when saturated with water? I think this is my main concern: if the CF blanket swells, it wouldn't take much to crack the stucco layers on top of it. Maybe this isn't really a problem? Lots of people seem to have stucco domes, and as David mentioned, in the tropics his must get really soaked during his wet season. I'm probably over-thinking this, and worrying too much about it, but hey...I only really want to build one of these suckers! Keeping it dry (somehow) still sounds like a good thing.

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  • Gulf
    replied
    Only if there is no place to relieve the pressure. Water boils at 212F @ sea level. The steam from it should be about the same. That is, unless there is no vent to relieve the pressure. If not, then the water will boil at a much higher temperature. That means superheated steam which expands more dramatically causing even more back pressure and even higher temps until something finally gives .

    That being said: If the oven and the insulation is totally dry, the outside of three inches of cf blanket should be near ambient temperature.

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  • johnnybrewmeister
    replied
    Looks like Tyvek melts at 275F, I can't imagine the outer layer (after 3" of CF blanket) getting anywhere near that warm, would it?

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  • johnnybrewmeister
    replied
    So I'm at the end stages of my oven build, and like the stucco dome look, but would like to waterproof it (I think). Question: why not use Tyvek? In hind-sight, I would think a layer of Tyvek (water proof, but breathable as it passes water-vapor) over the CF blanket insulation layer sounds pretty smart. I just now have a very thin scratch coat of stucco over my CF, so can't really do this, but am considering a Tyvek layer in-between stucco coats. Is this a bad idea? I'm in So.Cal., so a fairly dry climate, but keeping things as dry as possible just sounds like a smart thing to me. I'm looking into acrylic renders, and elastomeric paints, but as most people agree - completely sealing the dome is not a good thing.
    Thoughts?

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  • Alomran
    replied
    Kevink & Gasstag , George:
    Very interesting 2 points...Steam & vapor. I live in wet England and I know these 2 critical issues as an architect.
    Allow me to think loud here and I may be wrong.
    The ventilation for vapor is always absorbed by the cement particles in the perelite. However, if there is too much water between the dome shell and the insulating shell, then a simple single plastic tube reaching to the insulation blankey/void and letting it outside as a trickle vent will do the job for few months after which all vapor will be gone, then you can fill out with cement and seal it.
    As for the stem from cooking, it should evaporate with fire and I doubt it will seap thrrough the fire bricks.
    As for the damp dome you have referred to, the builder must have had a plenty of water somewhere that it was so huge id did not get absorbed by the cement particles during the curing process.

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  • david s
    replied
    I think it probably depends a lot on your local weather conditions. It is true that if the dome is totally sealed to prevent moisture getting in, then it also works to prevent it from getting out. Most proprietary renders contain a waterproofing agent that works to partially waterproof the render/stucco layer. I prefer to totally waterproof the exterior, but only after around 10 decent cooking fires (not including the curing fires) and to allow the insulation to communicate with the ambient air, I mhave designed a vent around the flue.This allows the release of damaging steam pressure as well as allowing moisture to find its way out. After our wet season(we live in the tropics) my oven needs a dry out with a few long slow fires to restore normal function.

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  • gastagg
    replied
    I am planning an igloo stucco finish. One of the considerations that I can't find any comments on is the amount of steam produced inside the oven and how that can negatively affect ovens that are finished as a igloo and sealed. I've seen a large portable oven that had a stucco finish and then a rubberized coating and it had huge water problems, and I don't think that the issue was from external water, but from internal steam that never escaped and then froze. Traditional exterior home finishes that use stucco also have some type of house wrap (Tyvek, etc.) that allows moisture to escape but limits water from getting in. I haven't seen anyone use Tyvek under a stucco finish, but I think it's a mistake to completely seal the dome. Enclosed domes have an "attic" with ventilation, much like a house would, where the moisture from cooking can eventually escape. Stucco is permeable, which is why you need to avoid sitting water, but to completely seal it would be a mistake in my opinion. I'd love to see some more experienced people weigh in on this. I don't have room for an enclosure and I prefer the look of the igloo, but I live in Minneapolis. So, I'm planning to use a pigmented stucco and cover during the winter and make every effort to protect against sitting water.
    Last edited by gastagg; 09-04-2015, 11:05 AM.

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