Written by Sustainable Farming Assistant, Eva Lara. Read more from Eva on her blog.
“Cob” is a traditional building material dating back thousands of years. Cob is made by mixing clay, sand, straw and water. It is a wonderful thermal mass, so it is a perfect material for all kinds of projects.
In order to make our pizza oven at Sutton Community Farm, first we needed a sturdy base that could hold heat; thankfully, we had Kevin’s building skills to help us with the building of a fantastic level fire-proof platform, with a top layer of reclaim fire bricks that formed the floor of the oven.
Simon Blackwell, our cob oven “guru”, made us split into two teams, my team was in charge of building a “sandcastle ” !?………
Materials required are:
- Clay (If you are short, Heavy Grogged Red Clay from a pottery supplier works well and gives a nice colour).
- Builders sand (Contains very small stones which are structurally important to the cob).
- Bricks for the doorway (Block paving or previously fired bricks work well as they take heat quite well ).
- Thick hardwood to make a door (ask friends if they have any lumps of oak knocking about that we can use to craft a door).
- Water.
- Straw (Pet bedding is fine as long as it is Straw and not Hay).
- Newspaper.
Base Materials:
- Bricks/Blocks/Railway Sleepers/Large Stones, concrete rings (Milton Rings).
- Drain rocks (Rocks that are quite large, so that when compacted they leave air gaps to prevent water wicking up from the footings.
- Gravel/Shingle (For footings and to pour in between drain rocks).
- Wine/Beer bottles. Ideally of equal size and shape.
Tools and equipment:
- Buckets.
- Shovels.
- Spades.
- Tarpaulins.
- Builders trowels.
- Wheelbarrow (Ideally a couple).
- Step ladders or pallets to aid in topping out ovens that are quite tall.
My team drew a circle on the oven floor with a big enough diameter for a pizza oven, we then cut a piece of bamboo around 50 cm long, to put in the middle centre of the circle and we placed it there with some clay, this stick will guide us to the high of the oven. By adding moist sand to the top of the base we started to mould our sandcastle, patting the sand with our hands to make the dome more compacted or air tight.
Meanwhile the other team were busy mixing the cob with their feet, they added sand, clay and water to make the cob and were enjoying a nice dance in the mud. It took a while but soon, the sand dome was finished and ready to be covered by wet newspaper pages, the cob was also ready when it was easy to mould it into a ball and hold the shape. We took turns so everyone had a chance at building with cob around the dome structure, it was easy to make small looking bricks and lay them next to each other patting them gently into place, similar to building a brick wall,
Simon did most of the work getting to the top and laying the last lump of cob, we then all added more cob to smooth the surface of the dome and gently patted the structure with a piece of wood. The last thing to do was to draw a small oven door that was going to be cut open on a later date, when the cob has dried out completely. Then we can take the sand and newspaper out of it and build our first fire inside.
This is the first layer of the oven, we can then add another layer of cob and straw if we want it too, plus a creative decorative layer to make the oven more unique, we can also build a small oven door made out of wood and build an arch with more bricks around the oven door.
You can see more photos of us building the cob oven on our Facebook photo album.