How to actually build with cob?
Roughly a third of the world's population lives in earthen homes, of which cob is only one type. In our modern society, building with cob or rammed earth is largely a foreign concept. It is rejected as primitive. Unfortunately, the prejudice against the idea of building with cob has arisen due to our comfortability with the status quo, and it enacts a general unwillingness to consider such an ancient building material and technique as feasible.
Cob is not only readily available and abundant, but also is well-insulated, durable, resistant to earthquakes and fires. Cob homes are healthy for the inhabitants and improve the air quality. Cob also yeilds itself to curved walls, arches, and niches, thereby allowing for artistic expression. Today, I will walk through the process of building with cob.
First of all, the building site needs to be adequately prepared. The site need to be compressed using a roller. There should be no soft areas which may potentially sink in later. Then, the area should be covered with a layer of sand to fill in any uneven areas.
The second step is to complete the foundation. A poured concrete foundation may be used or a cob floor. Once dried, the cob floor is extremely durable, and it may be walked on repeatedly without damage. Once complete, the floor should completely dry before walking upon it in order to avoid damage. To make it a non-skid floor, sprinkle some sand on the floor and seal it. It can also be painted if you'd like a different color.
Next, the cob needs to be mixed for the walls. On a large tarp, place two parts clay and one part sand. Add water and stomp on it. Mix it well, add a thin layer of straw. Mix it in, then add more straw. Roll the tarp around. The mixture will not stick once its ready. Keep adding straw until it doesn't flatten out when its dropped. Its important to get the cob mixture correct, otherwise the cob house won't last.
Next, form the walls. Create lumps with the cob and add a handful at a time, smoothing it out as you go. Cob should not simply be slapped on, this will draw moisture out of the walls. You want it to cure naturally. Be attentive that the sides remain straight, so that they don't become more thin at the top. You may use a ruler which is cut to the desired width of the walls. If electricity or plumbing is to be incorporated into the walls, then lay some metal conduit or plumping pipe where desired and work it into the walls.
The next step is to form the doorways and windows. Place a door frame, then build the cob around it in order to secure it. 2X4's may be sunk straight into the cob. The wet mud will dry out the wood and it'll be fine. For the windows also, sink a 2X4 into the cob and build the wall around the window frame. Prehung windows and doors may be used or you may construct your own.
Cob being a free-forming material, various artistic additions may be utilized. Colorful glass bottles may be placed within the wall to being color into the home. Rocks may be built into the wall for aestetic beauty. A bookcase, shelves, or other sorts of nooks and crannies may be constructed along with the walls. Railings of logs may be placed directly into cob stairs.
Upon completion of the walls, the roof can be formed with wooden logs, poles, or beams. From there, you can compose a roof with tin, a tarp, mud, bamboo, traditional wood truss, solar panels, or whatever one's preference is. The cob house will be mostly weatherproof. It won't break down when it gets wet, however, continual rainfall may erode the surface. Therefore, every ten years or so the outside of the home may need to be recovered with cob.
The cob home will remain relatively cool in the summer and warm in the winter. If you live in a colder region, an extra layer of insulation may be added to the center as the walls are constructed. Different materials may be used for insulation, such as plastics or styrofoam. Being wedged in the middle, there is no chance of the plastic seeping into the environment as a pollutant.
Sources:
https://diynatural.com/cob-house-construction/