In the Potter’s Kitchen: Food & Fire

Food and clay have run together for eons, developing a relationship between families, forms, and flavors. Family gatherings often bring up nostalgic memories of the flavors of food, long tables surrounded by conversations and recipes that have been passed down, or across, generations and borders, finding new and wonderful iterations and flavors affected by local ingredients or preferences.

When my studio practice ramps up, the amount of reclaim I generate grows exponentially and there are times when I can’t seem to keep up. One of the things that I have wanted to do with the reclaim is to construct a wood-fired oven, one that embraces the flavors that I love and the process of making food that connects me to places that I have been. Then came the COVID-19 pandemic quarantine, and looking at my vast amounts of reclaim, I made a connection. This was the perfect time to begin the wood-fired oven project; I could focus without the trappings of life distractions, and it was a great time to involve my family in creating the structure. From our experience in oven construction, here’s how you can make your own wood-fired oven.

Design, Site Work, Configuration

The most important part of the process is to configure a wood-fired oven design that works for you. Proximity of the oven to the house and the size of the oven are key, as an oven that is too big creates more work for the user, as does walking back and forth for ingredients and cleanup. In choosing my site, I wanted to develop what had become an overgrown garden. It was close enough for easy access, yet was far enough that eating a meal outdoors would be preferable to inside eating. In central New York state, our climate is rather wet in the non-winter months, hot in the summer, and snowy in the winter, so a good roof over the oven as well as a solid base were crucial.

1 Mix mortar, sand, manure, clay slurry, and water to secure the cobblestones.

Wood-fired pizza ovens can be constructed directly on the ground or elevated using other salvaged materials such as cinder block, but moisture and weather should be taken into consideration in your site plans. I excavated a space for a concrete pad that was 12 inches below the current grade of the yard. I filled the base of the site with 6–10 inches of #2 drainage stone and tamped it to a compact and level surface, framed it with 2×6 lumber, and poured a volume of concrete calculated for both weight and freeze/thaw concerns. My pad (see 2) was a 7×8-foot area, to accommodate the 4-foot clay oven, a 2×6-foot countertop, and space for wood storage. In knowing the overall dimensions of the pad, a simple equation for determining the amount of concrete needed can be found online to determine the amount of yards/bags needed for the project. I used a small two-bag concrete mixer and it was definitely a work and back saver.

My property abuts a farm field, and over time the farmer had stacked a large pile of cobblestones that had been excavated from the land. I have used these stones to edge gardens and various areas on the property, so I knew that I wanted to also use them in the design for the base of the oven.

Material Preparation

I wanted to keep this a low-cost project, but knew that I would have to purchase certain materials. I wanted to use as much of my reclaim as I could, but also was aware that clay alone wasn’t enough to build the structure. In researching cob construction, certain amendments are preferable, such as manure for binding, straw or other grasses for strength, sand for tooth and drying, and some mortar for strength. I purchased a 60-pound bag of sand for about $2, and used it in the mortar mix and as a support in construction of the oven’s dome. I also mixed the sand with clay reclaim to create coils and build the dome.

The first step was to create the base for the oven using stones and mortar. I used the following recipe for mortar:

I used a quart bucket for measuring out each material by volume. All of the materials were put into a large mortar mixing trough (a wheelbarrow will work) (1), and incorporated with a shovel until the mixture was uniform and thick. Each batch of mortar covered approximately one third of the length of one wall. My base measured to a 4×4-foot-square footprint, and the wall thickness was 10–12 inches thick. The cobblestone dimensions (up to the firebrick cook surface) were stacked about 14 inches high to a mostly level height.

2 Stack cobblestones in layers with mortar mixture troweled between the stones.

3 Fill each stone layer with crushed stone for drainage, support, and insulation.

The first layer of cobblestones was set in place, followed by a layer of mortar troweled on and in between the stones (2). Once the first layer was complete, the hollow interior of the base was filled with #2 drainage stone (3) that I had left over from making the concrete pad. This process was repeated two more times, and another load of stone was used to fill the inside cavity. The top height was approximately 40 inches tall and the stone inside was brought up to about 6 inches below the top of the cobblestones.

Next, a layer of straw dipped in clay slurry was laid on top of the stone (4). In the remaining space, empty wine bottles were laid down horizontally (5) and a wet mixture of clay slurry and sand was used to fill the space around the bottles and bring it up to a level surface just above the bottles. The layer of bottles creates an air space of insulation below the firebrick. This layer helps to keep the heat in the firebricks instead of it radiating down and being absorbed by the lower layers of the base.

At this point, leveling the top of the base was critical as the firebrick surface is stacked on this level. I leveled the cobbles, then added a final layer of mortar, followed by adding a final layer of skimmed sand to give a nice foundation for the firebricks.

4 Next, layer straw coated in slurry to create a heat break.

5 Place empty wine bottles on the straw layer as another insulation layer.

Cook Surface

With the base constructed, leveled, and sanded, the firebrick could be placed. Standard, high-duty, or super-duty firebrick should be the material selected as the repeated cleaning, heating, and cooling can all contribute to material fatigue and breakdown. These bricks can be purchased from your clay distributor or a local masonry supplier.

Starting at the front of the oven base, I laid the first brick softly onto the sanded surface. The next brick is lined up and touched to the edge of the previous brick and slid down the face to seat it. This process was repeated until a uniform pad of brick was achieved and all bricks were level. Avoid sliding the bricks along the sand, as even one grain of sand can keep bricks from sitting snugly together. Once the bricks were set, I used a rubber mallet to tamp the bricks down to seat them snugly. An extra course of brick at the mouth of the oven was also set to act as a skirt for easy scooping of coals and placing and removing the pizzas. These bricks are held in place by the door arch, so I had to be sure to have enough material underneath to support them (6).

Using a string compass, draw a circle on the brick surface using a pencil, having the edge of the dome come right up to the edge of the bricks (7). This is the interior of your dome. The diameter of the dome is 26–36 inches, a manageable size, but can be bigger if you wish. Just remember that the larger the dome, the longer it will take to heat up and it will need more wood to keep it at temperature while you cook.

6 Arrange fire brick edge to edge to make the cook surface. Tamp the brick to seat.

7 With a string compass and pencil, draw the dome circumference on the bricks.

Arch Door and Dome Template

Knowing that the brick door opening would need to be a bit more durable, I decided to make a firebrick arch opening. Dome height and door opening height are pretty crucial. The ideal ratio of the door height should be 62–64% of your dome height. So a 16-inch dome vault height should have a door opening of 10 inches tall. Knowing that my dome height on the inside would be 16 inches tall meant that my door opening would end up being right around 11 inches tall. I also wanted my opening to be slightly larger than my pizza peel, so I laid out the width at 12 inches wide. With the bricks on end on a piece of plywood, I laid them out edge to edge to create an arch curve, which I traced onto the plywood (8). I then cut out two of those shapes.

Using material that was shorter than the brick length, I made a rudimentary arch form (9) that I could stack my brick arch opening on. I placed small shims under the arch form, which allowed me to drop the form when it was finished and remove it to reveal the interior. I would normally use arch brick for a shape like this to prevent the bricks from falling as they heat, but I intended to mortar them and wasn’t afraid of them falling because of the low heat of the cooking temperatures. I wedged little stones between the brick to keep them at the right angle to the arch form, and stacked them to the center of the form. Once the bricks were in place, I mixed up clay slurry and masonry mortar, then troweled a layer onto the brick, making sure that it got in between each brick.
The clay slurry and straw mix added to the dome and brick arch also helped to hold things in place before moving on to the next step.

8 Set the door width; lay out the arch bricks and draw the curve onto plywood.

9 Place the arch form with shims under the form so it can be dropped and removed.

10 Trowel a mixture of clay slurry and mortar between bricks to hold them in place.

11 Coil pack a tight layer of clay and sand onto the dome, making a 4-inch wall.

Dome and Fire Drying

I filled the interior of the wooden dome structure with a wet sand mixture to support the dome as the clay reclaim mix was added over it. Mixing the sand with enough water to have it retain its shape without collapsing is crucial—much like a sand castle, I didn’t want the dome to crumble as I added the weight of the clay on top.

After the dome was filled with wet sand, I made a firm but wet mix of equal parts sand and clay reclaim (I used pugged material here, with slip or water to loosen it a bit), which is key to having a strong insulating layer for the interior of your oven (10).

Once combined, I formed the sand and clay mix into short, thick coils, then packed the coils in layers starting at the base of the dome (11–12). I made the thickness from the dome to the outside of the wall about 4 inches (the inner layer is 4 inches thick, and the outer insulating wall layer, which will be prepared and added in the next step, is 4 inches thick as well), until I reached the top of the dome and closed off the space. I packed the mix over the arch brick, bringing it right to the front face. You can encase the brick if you want to for aesthetic reasons—this is where the clay artist in you can pick and choose how your oven looks.

This clay-sand mix layer was allowed to set and dry to a hardened leather hard before the sand was removed from the interior. I waited three or four days before removing the arch form and the sand. Initially, sand can be scooped out with a small hand shovel or trowel, but use your hands when you begin to get close to the inner wall to prevent damage. Remove all of the sand and sweep out the interior.

The next step is to dry the structure. I built a very small fire in the mouth of the door opening and kept this going for the better part of a day (13). This fire drove off extra moisture, and in essence low bisque fired the interior of the dome to make it stronger so it could support the next layer of dome mix. I was afraid that without doing this, the moisture from the sand and the moisture from the next layer of dome mix could weaken the interior layer, and when I removed the sand, could potentially make the dome fail.

12 First layer of clay/sand mix on the dome, ready for the outer layer of insulating mix.

13 Maintain a small drying fire for a day after the arch form is removed.

14 Mix an insulation of clay slurry, hay, and sawdust for the outer 4-inch layer.

15 Pack the outer insulation of clay slurry, sawdust, and straw onto the dome.

Dome Insulating Layer

The final layer was mixed in smaller batches in a wheelbarrow by hand. I used clay slurry for this, nice and wet, and mixed in sawdust and straw (14). This material acts as a binder for the clay to prevent cracking, as well as to provide some airspaces in the mix to help hold heat. This wet mix was then packed onto the outside of the inner dome mix, about 4 inches thick (15). This layer goes a lot faster as you don’t have to compact the layers together as tightly and can move more in handfuls than in coils.

Because you now have two layers of clay on your dome—a dense mix of clay and sand on the interior and a light insulating mix on the outside, when the interior is at cooking temps—the exterior is cool to the touch. We all know that clay is a great insulator, and it’s really great to see it working here.

Now, you can sit back and congratulate yourself on completing a great project and making a great clay oven!

First Cook

Before you do your first cook in your oven (16), take a stiff bristle brush and brush down the inside of your dome, making sure to remove any leftover sand that could fall into your food. Sweep out the floor, and use a wire brush to clean the surface of the brick. I even went so far as to use the Shop Vac to really suck out sand and debris from all of the crevices and corners inside.

16 Thoroughly clean the cook surface then try your first pizza cook.

The interior should be low bisque fired from the drying fire, and the exterior has had some time to air dry, but still may have some leftover moisture. That will dissipate over the next few weeks, and depending on how often you use your oven, even faster than that. Laying out two logs, fill in between them with paper, twigs, and other kindling. On top of that, lay out a layer of logs edge to edge across the first two logs. Do the same in the opposite way for a third layer. Light the kindling and let the wood catch fire. Once the fire is burning well, use a shovel to push the whole burning pile back into the rear of the oven. I find that it takes about two hours to reach cooking temperature. Keep feeding the fire with logs and paying attention to the flame inside. The walls on the interior and the door opening arch will start to collect a layer of black soot around 400–600°F (204–316°C). As it climbs past 600°F (316°C), this soot will start to burn away, and at around 900°F (482°C), it will be gone. The coals can be spread out along the rear of the oven, and new wood can be placed as needed to keep the heat and build up the coals.

Let the oven cool a bit, and check the temperature by tossing a small amount of flour onto the floor brick. If it instantly catches fire, the oven is too hot. If you toss it in and it slowly browns, then smokes, then burns, that is where your temperature will be fine to cook. Roll out your first dough, top with your desired toppings, and slide it into the oven with a pizza peel. Turning it periodically to get an even cook, your pizza should cook in 4 to 6 minutes.

Jasper, Jeremy's son, with his own first pizza. Perfetto!

Things to Consider

You can cook more than just pizza in this oven! When finished with the pizza cook, close the oven door opening with a wooden plug made to fit, and wait until morning. The next morning your oven will be at a great temperature for baking your favorite crust bread, sourdough, or breakfast muffins. You can also cook ribs and steak in a nice hot oven using a well-seasoned cast-iron skillet. Also try to vary the type of wood you use to heat the oven. We used oak in our first cook and black walnut for the second, and you could tell the difference. It was subtle, but it was there. Apple or cherry wood are great too.

randall-oven

Happy building, happy cooking, and happy sharing. It really is a treat to see everyone standing around, cooking and eating food, and experiencing slow food at its finest.

Jeremy Randall received his BFA from Syracuse University and his MFA in ceramics from the University of Florida. He currently lives in Tully, New York, where he owns and operates Rusty Wheel Pottery, a making and learning studio clay space focused on community education in clay.

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