The Building of Green Camp’s Cob Pizza oven
At Bamboo U we are experimenting and building with more than just bamboo. We believe in using all kinds of natural materials. As a part of the development of Green Camp’s new location, we built a Cob pizza oven with a bamboo roofed structure in May 2020.
We wanted to build something that can crank out lots and lots of pizzas for hungry campers. We started designing the oven and bamboo roof structure following the existing conditions of the site. We made a scaled model of the oven with the roof structure. This helps us to visualize the structure and when building with bamboo, the model acts as the blueprint for the construction process.
Making of cob oven
We started with making a dry stone foundation by compacting stone debris and gravel. Then, we raised the oven base structure using random rubble masonry. Each piece of stone needs to be selected following its shape and put into place to lock in tightly with the other stone elements. To help secure the base we filled in the gaps between the stones with mud mortar.
Pizza ovens are designed to retain heat and radiate it over an even cooking area. To retain the maximum heat you need good insulating layers underneath the base, that is why the middle volume of the oven’s base is filled with the soil that has been compacted using wooden rammers and also a layer of reused empty glass bottles. Glass bottles are made of silica which is the primary constituent of sand, which has a high resistance to heat and can help with insulation. These glass bottles are covered by sand and leveled to the wall height.
The base of the cooking area in the oven needs to be a flat surface where pizzas are placed to be baked. This top layer is made of tightly placed flat burnt bricks. Since some of our bricks were uneven, we sealed the gaps using a lime paste.
To control the flow of heat we designed the dome in proportion to the diameter of the base. The center height of the dome is 75% of the base diameter and the height of the door opening is 63% of the dome height, so that smoke can easily escape from the top edge of the door opening.
Once the base was ready we made the formwork for the oven dome. We made our template using bamboo stips known here as ‘lidis’ and placed them on the top of the oven’s base. The formwork is built using sand similar to how we build a sandcastle. We built a solid sand dome, which is later removed once the dome is built and secure.
During this process, we were also busy making cob so that once the sand dome was built, we could start building the dome immediately. Cob is a mixture of clay, sand, straw, and water, mixed manually with our hands and feet. To have a good quality of Cob it is suggestable to have 20-30% clay and 70-80% sand depending on the soil available locally.
In building an oven dome we need to have a thermal mass layer and a thermal insulation layer to hold good heat for baking. So the first layer( thermal mass) of cob mixture consists only of clay, sand, and water. Whereas the second layer (thermal insulation) of the cob mixture consists of clay, sand, straw, and water. The straw acts as an insulation material. We also added bamboo lidis between the two layers which acts as fibers and helps to avoid structural cracks of the oven dome.
Once the oven was built, we cut the door opening and pulled out the sand, molded the opening with cob, and made a beautiful teak wood door for the oven. This door shape is achieved by using the catenary arch technique. The catenary arch is a type of architectural arch that follows an inverted catenary curve. Catenary arches are strong because they redirect the vertical force of gravity into compression forces pressing along the arch's curve. This has been employed in buildings since ancient times.
Sai joined the Bamboo U team in March 2020 as Research & Development Manager. He is also a natural builder and an architect from India. He has managed many mud and bamboo projects over the years.
March 22- April 2, 2024
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