What the Farm ?! Building a Cob Pizza Oven on Camera – Hive 678

What the Farm ?! Building a Cob Pizza Oven on Camera

A local, and very cool, TV show built a cob oven in the backyard, and hosted a pizza party with pizzas baked in the oven.

In October, I was contacted by John Wimberly from Clerisy Entertainment, who was looking for a place to build a cob oven for a TV show he was working on, called What the Farm?, starring Jayme Melrose, director of Common Roots Urban Farm. Coincidentally, Jayme is also a former resident of this house.

They thought to ask me because I:

a) have the space
b) have worked with Clerisy before
c) am really into local food, community, and sustainability,

and most of all because I sort-of-maybe should know how to build a cob oven, since I have participated in building a couple of them in the past, and had my own natural plastering business.

I jumped at the chance to have a TV show pay for and organize the building of a pizza oven in the backyard, and offered the space, but I also told them that I’m no expert, and didn’t have the tools to do the woodwork myself.

Enter Dominic. Dominic is a friend from the natural building/earth construction world, who also lives down the street from me, has his own small projects woodworking company, and has already worked for a show with Clerisy before.


Dominic did the cob oven research, and preliminary construction, while I was the on-camera, earth construction personality.

Unfortunately, I didn’t get very many photos of the project because my hands were muddy most of the day, but I will explain it as best I can. This is just a brief explanation of cob and the construction process. Definitely do more research, or even contact me before you decide to build a cob oven in your own backyard.

What is Cob?

Cob is a type of earth construction made from clay, sand and straw. It is a natural and very environmentally friendly building material. It is great for ovens because the mass retains the heat.

How a Cob Oven Works

This style of cob oven only has one chamber. The fire burns for a couple of hours inside to heat up the cob. Then the burning logs are scraped out into another vessel, the firebricks are wiped off, and the pizzas can go in. The oven retains heat so well that it stays hot long after the fire goes out.

Construction Process

Constructing the Foundation with 4 x 4’s

I didn’t have a lot of time to choose the site for the oven, so just in case, I wanted to be able to move it with a forklift if absolutely necessary. For this reason, the base is a ‘log cabin’ style stack of 4x4s on a gravel base. Dominic did all the woodwork at his workshop down the street.

Insulating the Base with Perlite and Empty Bottles

The first day of filming, we built the insulated base and firebricks. On top of the “log cabin” there is a piece of plywood that holds the insulation. We built a little wall of cob around the perimeter of the base to make a bowl. Then we filled the bowl with empty bottles, and poured perlite over them, and packed it down. Next, we carefully spread sand on top of the perlite layer, being careful not to mix them, and levelling the sand to make a stable base for the firebricks. Then the we laid the firebricks in the sand.

Making the Mold with Wet Sand & Cobbing the Cob

The method for shaping the interior of the oven is so simple and ancient. We molded a big pile of damp sand in the shape that we wanted the cavity of the oven, covered that with newspaper, and then built the cob onto that formwork, making sure to pack the cob tightly together.

Then we waited days for the cob to completely dry before digging out the sand, leaving a hollow cob oven.

Insulating the Oven with Slip Straw

After we have the cob oven, that seems like we’ve made a lot of progress, but there’s still a lot to do. The first layer of cob is the thermal mass that stores the heat, but then we have to insulate it so the heat stays in while we’re baking.

The insulation is made with slip straw, which is like a salad of straw tossed in a dressing of clay slip. That gets packed onto the cob layer.

Plastering  the Outside

Finally, to protect the insulation, a couple of layers of plaster go over the slip straw. The first layer helps to tidy up the shape of the oven, and the second layer is the finished, smoothest layer.

Eating Homemade Pizza

For the last day of filming, we had a pizza party, to enjoy the fruits of our labour. The show was about local food in Nova Scotia, so they brought toppings from local farms, and even dough made with locally-grown flour.

The Show

I haven’t seen the show yet, but it’s supposed to air on Eastlink in Spring 2018.


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