The inaugural use of the clay oven
If you are into permaculture, eco-construction and/or just cool garden projects, then building your own pizza oven has undoubtedly made a blip on the radar at some point. For me, I first encountered them on Ometepe Island in Lake Nicaragua, where it seemed every other hostel, hotel or farm was hosting a weekly pizza night. I was volunteering at a small permaculture project (Totoco Farm), and we were no different — for all the volunteers, Wednesday night was pizza night.
At that point, I was still relatively new on the scene, and while I had done some eco-construction with earthbags, I had never taken on my own project. So, when the farm’s owner Martijn told me about the building process, I noted it but didn’t really think I’d be building my own within the year. My, how times change. Just a couple of months after leaving Totoco, I took a job in Panama with the idea of putting organic gardening and permaculture practices into play on a small piece of vacation property. Building a pizza oven immediately came to mind.
Pizza dough at the ready in Nicaragua
I had been very interested in cob building techniques and was planning on volunteering at some places in the coming year to learn the ropes, but now I was going to have to teach myself. I started researching cob ovens and was thrilled to discover how much of the material was on site. The soil was clay, and after testing it, I knew it wouldn’t even require separating. There was also plenty of leftover sand and bricks from a previous building project, and all of the materials for building the base — a few breeze blocks and some nice, thick cuts of teakwood — were here too.
- How to Test Your Clay Soil: I learned two methods. One was slightly wetting the soil, rolling it into a sausage shape, and forming it into a circle. If it’s malleable enough for that, then it’s a high enough percentage of clay to build an oven with. The other method, which worked better for me, was rolling the moistened soil into a ball. After it dries, if you can pinch it tightly between two fingers without it breaking, then it’s good to go.
Then I ran into a problem: no one knew where to find straw. Hay was available, but everything I’d read said hay didn’t work. I started considering alternatives, using different kinds of hardy grasses that we had access to, but ultimately I didn’t have enough faith in them. I thought of coir (coconut fibre), which we did have via the coconuts we ate, but harvesting enough of that would have been a mammoth, time-consuming project. In the end, I did a search for no-straw clay ovens. The site I found is the reason this article is not a step-by-step guide.
The Clay Oven website had it all, from a Kindle-friendly book for downloading, to an illustrated, absolutely free online guide through the process. I honestly could not describe the steps any clearer and certainly couldn’t provide as much info in one article as this entire site does. Thus, when it comes time to build it, follow the link, and for now, keep reading for my experience.
Long before collecting the clay and sand, I built the plinth, or platform, upon which the oven would sit. There are lots of ideas for this. Most of the YouTube clips I’d seen and articles I’d read made a solid platform, out of either stone, cob or brick. However, I noticed a few that had built ovens atop tables, and I liked the idea of having a spot to store the wood. So, for my plinth, I stacked a couple of rows breeze blocks around the side and the back then built a sturdy teakwood top to go atop them.
Clay test on the plinth
It worked out fabulously. Not only had I created a spot for wood, but also the base of the oven became a clay-testing zone. Not wanting to ugly up the structure with bare breeze blocks, we (a volunteer, my wife, and I) decided to cover the blocks with clay and used the opportunity to experiment with how to handle our sand-water-clay ratios. The base could not have pleased me more. The clay held fast to walls, inside and out, and just under a square meter of floor space provided plenty of room for storing wood.
- Mixing the clay was a completely new thing for me, and, to no avail, I kept trying to defer to others with experience making pottery and whatnot. In the end, I learned that too much moisture causes cracking later and too little makes the clay harder to mold. For us, the ratio ended up being two parts sand to one part clay to one (slowly added) part of water. However, no exact measurement exists because the purity of materials, humidity and so on come into play. The test we learned was to make a fist-sized ball, drop it from shoulder-height, and if it splatted but stayed together, it was good.
The next feat was the oven floor, which I was supremely concerned about. I’d used an oven with an uneven floor before and found it horrendous. Unable to slide the pizza peel (the shovel-sized spatula) cleanly beneath the pizzas, we ended up ripping the crust and leaving toppings spread all over the place. I wanted the bottom of this oven to be tip-top and straight as a die.
Applying papier-mâché to the great sand castle
There are special heat-resistant bricks available, but I’d elected to use some ratty, chipped specimens I found in a pile. After a good buffing and sorting, I managed get enough decent ones for the center of the floor, where the peel would slide. Then, I discovered there were just barely enough bricks to cover the floor space in total. Nonetheless, I experimented until I came up with a good pattern.
- Floors for the ovens always seem to call for a layer of glass bottles and sand to go beneath the bricks. It acts as a sort of insulation. We had plenty from our waste-reducing program. However, I want to warn other builders to make sure that you leave ample space to include this layer of bottles. I actually had to install a temporary clay wall to have enough room for the top layer of sand, a must for leveling the bricks.
Luckily, just as the plinth had worked, so did the floor. I constructed it with the patience of a saint, testing each new piece laid in, running a straight piece of wood across the surface to insure it didn’t get hung up on anything. This piece of the puzzle, as I’ve suggested, as did The Clay Oven website, is worth lingering on, getting right, because once you move on, it can’t be fixed. Though inexperienced, I’d say I nailed it.
Finishing touches for the first layer
Then came the layers of the oven dome. For the first, and most important layer, you shape a large mound of sand to support the clay while it dries. My wife and a volunteer did this while some other volunteers and I mixed the clay in the same ratio as before. This time, with much more quantity needed, we traded off on mixing duty, which is most easily done by dancing barefoot in the sludge. Once it passed the test, we created an assembly system of brick-makers and bricklayers. It went up in a couple of hours.
- I got the bright idea of mixing my clay in an old wheelbarrow tub, thinking it would keep the mixture from spreading. It did hold it just as planned, but I later found out that mixing is easier when the materials can be pressed flat instead of forming big pockets of sand. For some reason, it took me ages to correct this. Just do it on a tarp or piece of plastic sheeting.
The drying process is nerve-racking. Inevitably the oven is going to get little cracks as the clay dries and shrinks. Adding to the first layer’s stress is the need to catch it semi-dry to cut out the mouth of the oven. The Clay Oven website suggests a couple of hours of waiting, but in the humidity of the Panamanian rainy season, we waited nearly two days, nervous that the moist clay would sag or fall. In the end, with nothing more than a kitchen knife, we cut out the opening to reveal another success story.
Happy with the tunnel and chimney
We had to wait for nearly a week for the oven to dry out completely, the final step being to light the first fire in it. From there, it was time to put in a little tunnel opening and smoke chimney coming from the mouth. So, we pulled the sand out of the shell and piled it where the tunnel would go. We had enough clay mixture left over (stored in a sealed plastic bag) to finish out this part of the project. And, at this point, the oven really took shape.
- In creating the chimney, I wanted it to be all clay, just like the rest of the oven, so I came up with the idea of putting a tapered wine bottle wrapped in wet newspaper (You do this so the clay won’t stick to it) atop the mound of sand built for the tunnel. It worked like a charm. We just formed the clay around it, and once the clay was dry, the bottle slid right out.
The next layers, though more material heavy, went equally as smoothly. We developed a basic system of one person mixing and making bricks while two people would put the bricks in place. The second layer required wood shavings instead of sand and seemed to soak up a little more water, which in return caused more cracking as it dried. Nervously, we checked throughout the day and week, hoping it wouldn’t suffer any major damage.
Firing a pizza with a volunteer
We were repairing the cracks every morning before realizing that it was better to wait for the crack to form all the way. What was happening was that, each time we repaired the not completely dried crack, it would form again and again, until ultimately we sealed in a massive air pocket beneath the surface. For the third layer, we pushed in these air pockets and filled them with the original sand-clay mixture from before, and from which the final layer is built.
- Obviously, as the outside of the oven expands, the layers require more and more material. Each layer adds about seven centimeters of girth to each side (fourteen to the circumference). Consequently, the last layer took us nearly twice as much material as the first, so best to keep that in mind when gathering the sand and clay.
Once the third and final layer was on, it was apparent we’d created a masterpiece. Using extra clay, I built a little removable chimney plug and, with some scrap pieces of teakwood, I pieced together a thick door to trap the heat for baking bread with leftover pizza dough. Then, it was time to fire that puppy up and see how it cooked. Some twenty or so pizzas later, we were all feeling pretty satisfied, and there was plenty of ash to sprinkle on the garden.
What it’s all about
Special thanks to Emma Gallagher and Annti Suomi for their photographic contributions to the project and this article.