Originally posted by dogshark58
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2) The red stuff is RedGard. A liquid waterproofing membrane. I put it on my slab to prevent moisture in my slab from wicking up in to my board and blanket insulation. I had it on hand, so I used it. RedGard is NOT vapor permeable, so I would NOT use it over the render shell that covers the insulated dome. I DID waterproof my render shell but with Thoroseal. Thoroseal is a cement-based waterproofing that is waterproof (liquid waterproof) but it is also water vapor permeable. Water vapor can pass through it, but not liquid water.
In an idle oven, one sitting over a wet winter for example, the oven structure may absorb moisture simply due to latent moisture in the atmosphere. When I fire my oven after a period of non-use, the fire will try to drive that moisture out of the oven. While the moisture can NOT pass through the RedGard (vapor impermeable) it CAN pass through the Thoroseal (vapor permeable) and then in to free air. I also have a vent at the apex of my dome. Moisture vapor driven out of the dome structure by the heat from a fire does exit the oven structure through that vent as well.
Try to keep water out with proper detailing of your build. But plan on it getting in, thus provide an appropriate escape path. Just in case!
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