SET COMMUNITY GARDENS
AMSTERDAM IJBURG

As part of the community building and social gardening process at SET Community Gardens we wanted to build together an earth oven. The oven as the symbol of the heart of the community, fire, where you can make food, food based on shared recipes, using the vegetables, herbs from the garden. Food has always played a central role in the life of people. Making food together, making slow and good quality food is an important element in the life of the garden community. The process of making of the oven was as important as the final result. Learning something practical, doing by hands, together, as a process, learning from the mistakes, fixing, working based on circulair values was all teaching us how to follow an alternative path to the capitalist logic. Working in a simple way, with care, attention, slowly, together.

Phase 1 – building the oven – July 2024

Financed by the New European Bauhaus Prize and Oost Begroot (Gemeente Amsterdam) in JULY 2024 we realized our dream building the earth oven according to the plans and with the guidance of MARTA ROTA & QUITA SCHABRACQ architects. Read the detailed report here.

The oven in the SET community garden was built as an addition to the outdoor kitchen. Constructed with a plinth of recycled bricks, the earth dome creates a ‘warm hearth’ that brings people together to unite over a shared meal. By cooking together in the oven, the project aims to create social networks and promote community living.

Through a two-day participatory workshop, around 10 people from the community built the cob oven together, setting a symbolic tone for the project as people of different backgrounds and ages participated. They were given a theoretical introduction to building with earth and then had the opportunity to get their hands dirty. The intention of this reflection report is both to document and explain the process, and function as a manual of the different steps taken to construct the oven. As well as a document of reflection, in which we can mention the difficulties and problems that we encountered, the way we have dealt with it in the process, and thus what we have learned.

PREPARATION
The technical design of the oven was prepared and worked out by Marta and Quita, with a brick base, a steel door and chimney, and a cob dome for the pizza oven. Based on the information from Dora, Marino, Tayfun and other members of the community, we designed a pizza oven with a table and barbecue. Sketches and technical drawings were made for the construction. The community was activated to collect both bricks and bottles. Before we started with the workshops, flyers in both Dutch and
English shown below were made to invite people form the community to participate in the making of the dome.

Reflection

As the community exists of many people with knowledge and skills, perhaps it would have been good to create a timely moment for giving feedback on the design, and making decisions regarding adaptations of the design together. Now, different feedback from members of the community came close towards the start of the construction, which is quite late into the process.

PROCES OF MAKING

For the constructions of the oven, 10 steps were taken that will be
expalined and reflected upon in the following pages.
Step 1: Gather the Necessary Materials
The following is a list of the necessary materials that the community has collected, and where this has not been possible, we have
purchased what is needed:

• Recycled bricks (around 300): They are used to build the
  plinth on which the earth dome is built on. The number of
  bricks depends on the height of the plinth.
• Empty wine bottles (around 60): These are used to insulate
  the base to prevent heat loss into the plinth and the ground.
  They are placed under the chamotte tiles.
• Sand: For making the ‘sand castle’,as a formwork for the cob.
• Earth: For making the cob mix. We bought it from Rokus Oskam (https://oskam-vf.com/). The earth is Dutch and comes
  from the Hondsrug in Emmen. It comes from the north during
  the ice age.
• High-fire resistance chamotte tiles: They will form the oven’s
  floor.
• One bale of straw: For the cob mix. It acts as an insulation
  layer.
• Water: For mixing cob.
• Tarp: This is for making the cob mix
• Metal sheet (6mm): For the oven’s door and base.
• Metal pipe (diameter 150mm): for smoke extraction.
• Cement: For the mortar of the bricks of the plinth

Step 2: Build the Plinth
The size of the oven determines the size of the base and the diameter of the plinth. A base diameter of 1.1 meters is sufficient for a cob oven to cook one or two pizzas at a time. Once the design was approved the process of building the plinth of the oven began. Alexander Schabracq, an artist and blacksmith, built the base of the oven using recycled bricks collected by the community. First, a minimal foundation was made as a support for the bricks base, by digging a ridge into the ground, and filling with a small layer of cement.

Afterwards, different types of bricks were combined to create a colorful composition. The design of the oven integrates a worktop for food preparation and a barbecue on the side. Alexander working on the plinth. The bricks were joined together with mortar, using a trowel to smooth the mortar between each brick. Once the plinth was complete, the metal door was then placed in the right position. For the base of the oven, we used a 6mm sheet of metal, which was embedded in the layers of bricks. This created a sort of basket base on which the sand was placed. The wine bottles were packed tightly together, with more sand in between and smoothed down to create a flat surface.

Step 3: Build the Floor of the Oven
Once the base has been built, the next step is to build the floor of the cob oven. As a cob oven can reach temperatures of up to 700 degrees Celcius, it is important that the floor of the oven is fireproof and can withstand extremely high temperatures. For this reason, we have used chamotte tiles (high refractory fireclay tiles 30x40cm). First a tiny layer of clay mixed with sand was put at the bottom of the oven base. Then the plinth was filled with the glass bottles, layed tightly packed together. Caps were removed were possible.

Afterwards, a layer of sand was layed out over the bottles, covering the whole base, leaving no bottle visible. Tayfun shared his skills and tools to properly level the base. The chamotte tiles were placed on the leveled sand surface, as close together as possible. The edges were filled in with leftover bricks, that where needed, were cut into the exact shape by Tayfun to make the whole base fit tight. It is important to remember that the oven must be constructed in such a way that there is sufficient radiant heat into the oven. Secondly, you need sufficient insulation around the stove to retain the heat and keep it inside.

Step 4: Build a Sand Form (Dome)
The best way to build the dome of the cob oven is to first make a mound of sand, which is then covered with the first layer of clay (5cm without straw). The sand will act as a formwork and will be
pulled out at the end, leaving a hollow dome. Making the sanddome together.
The sand must be of a consistency suitable for building a sandcastle. When building the sand dome, it is important to know that the height of the door must be less than the height of the dome
to allow for better air circulation.

Once you have achieved the desired shape, you can cover the surface of the dome with newspaper to prevent the sand from mixing with the first layer of cob. The newspaper is sprinkled with
water so that it sticks well to the sanddome. Covering the sanddome with several layers of newspaper.

Reflection
We calculated way too little sand! We bought 9x 25 kilo bags, but we needed about double the amount. Luckily we could ‘borrow’ the sand from the childrens playground for now, as the sand would be returned after the drying of the cob layer. The size of the sanddome is something we should keep track of better. We had less space than the anticipated 20 cm towards the edge. It doesn’t have to be a problem, but its good to keep in mind. You don’t want the cob layer to be less than 15 cm.

Step 5: Mix and Apply the First Cob Layer
The purpose of the first layer of cob is to act as a thermal mass to radiate heat back into the oven. No straw is added to this mixture. Water is added to the earth as it is trampled until a doughy consistency is achieved. We mixed the material with our feet. The ideal moisture content for cob is between 15% and 35%. Using our hands, we formed the mixture into golf ball-sized lumps and placed them on the sand dome. We started at the bottom and worked our way up, creating a 5cm layer over the sand mould.

Step 6: Mix and Apply the Second Cob Layer
This second layer is for insulation. It’s responsible for keeping the heat inside the oven. To this layer we added straw. After mixing the soil with the straw and water, we achieved a consistency that could be molded into clumps.

Starting from the bottom and working up, we applied a thick layer (between 10-20 cm) around the oven.

Step 7: Add the Final Layer of Plaster
A final layer of plaster (2cm) was then applied as a final step. Earthen plaster is not waterproof, so a wooden pergola will be built to protect the oven.

Reflection
When mixing the cob, perhaps we used more water than needed. In the last layer, to make it easy and smooth to work with, we kept adding water, but ultimately that leads to shrinking as the cob layer dries.
Another point of reflection is about the mix. The second layer was the loam layer mixed with straw. The straw acts as a reinforcement of the loam, and prevents cracking. Perhaps in the finishing last layer of loam we could have added some sand in the mix, to prevent cracking in the outer layer.

Step 8: Drying and removing the Sand
Once cob dome has dried in a few days, you can remove the door and the sand form, until the paper layer. Pull out the sand from the doorway to reveal your cob oven. Remove excess clay or straw from the oven’s surface using a trowel and broom. Removing the sand until the paper layer. The oven had to be covered and uncovered every few days, as it doesn’t have a roof yet, and there were plenty of rainy days this summer. In conversation Tayfun, Marta and Dora made the plan for the pergola roof and layed out as seen below.

Reflection
Some cracks appeared directly after drying. This does not have to be a problem. It is important to remove the sand from inside the dome so that the cob layers can dry evenly from outside and inside at the same time.

Step 9: Fire the Cob Oven
Once the cob stove is dry, it can be fired. The fire can be lit and left to burn for a few hours. Cracks will probably appear, but there is nothing to worry about. This is normal. Later, some cracks
can be repaired by making the same mixture in small quantities.

Reflection
The first fire in the cob oven was rather large. As seen in the picture the flames are high into the oven, touching the cob layer. Perhaps the fire ‘stressed’ the cob layer a little bit too much for the first time. More cracks appeared in the cob layer and smoke came from the cracks. For a second time, the fire would be better made smaller, and perhaps even without the wish to make pizza. On the other hand the pizza’s came out well, and the first pizza party was a succesful one. The oven has proven its functionality
for making pizza.