Breathable stucco render?

[waynespizzaworld]

Thinking about the best way to treat the render on my next oven project. The last oven had a stucco render and looks good but here in Canada the winters are very wet and cold. Even though there will be a roof over the ovens I build I want to make sure the stucco treatment is working as well as it can to hold out the outside moisture in the air and yet let the oven somewhat breath for after winter start ups when there may be moisture collecting in the inside of the oven during periods of the oven not being used. The last project had the completed oven sit for 4 months during wet weather and the customer has reported the stucco warm to the touch upon first firing after the winter inactivity. IF its steam inside causing the warmth and I feel it is, then one would want this outer stucco layer to breath somewhat to let out the moisture. Has anyone built a vent on top of the stucco dome render to let out moisture if it collects inside the oven and then also go with a coating on the stucco to try and make it more water proof. I was thinking if a person went with a small vent on the top of cook dome you could make the stucco more waterproof with a top coat of something, but maybe just the vent would be worth considering.

This also bring up question I have thought about, I see some ovens with a tiled outer covering. I would think its only the grout lines that would let out moisture as the tiles are not porus at all so how do these ovens work if and when moisture gets into the inside of the oven. I would think the steam would then get trapped between cook dome , insulation and tiles?

[Wiley]

Re: Breathable stucco render?

"Has anyone built a vent on top of the stucco dome render to let out moisture if it collects inside the oven and then also go with a coating on the stucco to try and make it more water proof."

Yes, but my gap is around the chimney rather than at the top of the dome. The gap is about 3/4 inch between the shell and the SS chimney. This gap is to allow heated air and moisture to exhaust from the region between the inside of the exterior dome and the exterior of the refractory. Since the interior of my WFO is a steel dome there is virtually no exchange of gases or moisture between the inside of the oven and the refractory overlaying the dome. But I had to allow for moisture in the refractory to escape (trapped during construction) and for atmospheric pressure between the inside and outside to be the same. The gap is protected from water intrusion by the roof over the whole oven.

I built my WFO so that should the need arise I could separate the exterior shell from the base and lift it free of the WFO. It is a free standing structure separate from the WFO itself, a dome over a dome. This I believe is why I have not had issues with cracks in the stucco associated with expansion of the WFO when heating. The exterior dome is at ambient temp; the biggest temperature extreme is between the side exposed to the sun and the side in the shade.

This allows for a totally waterproof outer coating of the stucco.

Hope this helps,
Wiley