Weekend Warrior: How to Make A Cob Oven

Open flameIf you are looking for a project to complete over the course of a weekend, building a cob oven is a great idea! Cob ovens are baking ovens that are heated by lighting a fire inside. They can be made with natural materials. With this project, there’s no need for exhaustive effort or complicated equipment. These ovens can bake pizzas and breads, and create mouthwatering roasts. Food cooks very quickly since the oven is superheated. Expect pizzas to finish in about 5 minutes, while a large duck may take just 45 minutes to roast.

The main necessary materials for this project include clay, sand, sawdust, firebrick, gravel, and old cinder blocks. You’ll want to build a foundation that raises the oven off the ground and onto an appropriate working height. Typically about 40” off the ground is a good average height. Build the base with masonry material – clay, sand, straw, etc.

Once this base reaches about waist level, fill it with a non-compressible material like tamped gravel. Include an additional 4” layer of sand, extending just above the sides of your base. Pat down and level out the sand. Next, build the floor of the actual oven with firebricks, packing the bricks close to each other. You’ll want to make sure that the bricks are level. If necessary, take some extra time on this step. The nicer the oven floor, the fewer problems you will have when the oven is up and running.

The next step is making the dome for the oven cavity. Start shaping the dome with sand – the width should be the diameter of the baking space you desire. Make the height of the dome 75% of whatever your width is. Add a layer of newspaper over the dome so when you dig out the sand, you’ll know when to stop digging.

Build the clay mass over the dome, keeping the first layer to just sand and clay. Ensure that the mixture has a sticky consistency, but also enough sand so that the layer won’t shrink and crack too quickly over time. This generally means between 20-25% of total clay content. Make this layer about 4” thick all the way around the sand dome.

Once the clay mass is completed, add the insulation layer of straw and a bit of clay. To complete this step, use a clay mixture that is 50% clay and 50% sand. Wet the mixture so that it has the consistency of a milkshake, adding plenty of straw to soak up the mixture. Add the layer to the dome so that it is about 6” thick. This layer will help keep the heat inside the oven for as long as possible.

Sculpt the door in the insulating level. If you are not making a chimney, the door should be two-thirds as high as the inside dome, to allow fresh air to feed your fire. Allow the oven to dry thoroughly and then pull out the sand with a clay spade chisel from EquipSupply.com to create the opening for your food. Once done, let the oven dry for a few days before you use it for the first time.