Options to Finish Outdoor Build

[kevdel]

This spring we built a 27" internal diameter pizza oven. We've wrapped it in fiberglass insulation and then added about 4 layers (1.5 inches) of lime/mortar cement/mortar sand stucco mix. We'd like to add one more layer on top of this to make it more weather proof.. we have more insulation left over to cover it so we could do a second insulation + stucco.

Would a perlite/cement mix over the top of a floating insulation layer be a good top coat to make it weather proof? I would like to minimize cracking

The oven has been 75% fired and we also we live in iowa so we have hot summers and cold winters.

[SableSprings]

Welcome to the forum Kevdel!

We have been advising people to finish curing their oven before applying a final outside render or to include a vent through which moisture can escape during the cure/firings. Perlite/Cement (I call perlcrete) is not waterproof, so putting on another layer will simply add another layer of "wet" that may seep down into the lower levels or provide another sponge to the mix. There are acrylic additives made for cement based renders to help seal an outer layer, but cracks in renders are pretty hard to avoid and both the ceramic batting and insulating cements will absorb water from air humidity alone. If you really want "waterproof", the only way to be 100% dry is to build a "dog house" enclosure over the oven. Using the cement acrylic additives works pretty well, but you must be aware that there will always be a need for maintenance and sometimes a couple extra low firings to force out moisture absorbed during periods without firings.

The problem of waterproofing a dome has certainly been high on the topic list for years on the forum...I wish we had a permanent, inexpensive, and reliable method that was maintenance free. It still comes back to the "putting a roof over it" as the best method. Hope that helps a bit...putting a tarp over a cured oven during the winter when it's not in use is advised (but you will need a couple drying fires in the spring to bring it back to an efficient working level.)