(TL;DR: photos of cob oven construction below / timelapse video / basic how-to guide)
I visited my friend Dan Paluska in late August at Monkshood Farm and Nursery in Stuyvesant, NY. Dan and I, apparently in parallel without knowing it, had both been looking into cob, that mysterious and alluring construction material that’s greener than anything you’ll find labeled “green” – it’s literally a mix of clay, water, sand, and straw/sawdust, or whatever you can find to suit the purpose. “Green construction” might sound like a newfangled concept, but hey – this is how people have been building for thousands of years, and it works. Beautifully, actually.
Anyway, a few chance emails later, we realized we we both wanted to get our hands dirty with this “cob” business we’d read about everywhere but had never actually seen in person, and Dan thought an outdoor oven would be a good addition to the farm. So we both did a little research, I wrote a little guide you can find here, and we took a weekend and did it. The guide is pretty exacting in some parts, but we didn’t have any way of reading it on the fly (neither of us thought to print it), so we used the basic ideas (and even ignored some of those) and the oven came out great just the same.
There was a swimming hole near the farm and we took a bunch of buckets (and a bunch of people) and had a clay digging / swimming party. We got a couple bags of pre-moistened sand, but also used some extra sand from the driveway. Some of the sand in the dome went in totally dry, and we used a cardboard base and a bit of white plastic tarp instead of newspaper to cover the sand dome and help it keep its shape. While we were mixing the cob, we had a little trouble sometimes finding the right consistency – sometimes we’d use the right ratio of clay to sand, but due to the clay and/or sand that we were using, the texture would feel too sticky or too grainy. So we had to do some adjusting and, in the end, realized that 3:1 is a good starting point, but considering that you’re pretty literally using the earth under your feet which varies from place to place, adjusting as you go to get a good texture is the most important consideration of all. (The last couple pictures are of minor cracking that we spotted the morning after building that first layer, and I think those are from there being a little too much clay, without enough or the right sand to hold it all together.)
I wasn’t able to stay long enough to see the first layer of cob dry / help get the outer insulation layer of cob onto the oven, but it’s a process very similar to the first layer. Also, we completely succeeded in the “getting our hands dirty” objective – so dirty that I couldn’t take any pictures in the middle of the process, but these pictures at least should help visualize a little bit what’s written in the guide. Also, here’s a little timelapse video that shows us building, including the middle part that I couldn’t photograph, like stamping in the stuff to mix it. It was fun.
Although I haven’t been there yet to try the finished oven out, Dan says it’s great. Briefly, as far as the end product is concerned and in case you don’t know anything about this type of oven, you start a fire in the back of the oven and let it fire for an hour to a couple hours. The cob soaks up and holds the heat, and after you’ve cleared out the inside of fire debris, you can cook pizzas, breads, etc. – works like any oven. I’ve heard of cob ovens reaching and maintaining 700 degrees. I don’t know how capable ours is, but the purpose was to use it as a pizza oven, and it sounds like it was a success despite our off-the-cuff approach.