Cob House Build START to FINISH in 10 Minutes

This video is a time-lapse of a cob cottage workshop that took place over five weeks in the North Carolina mountains. We built this mud house using local natural materials including clay, sand, straw, and roundwood timbers. Using the footage from this workshop, I was able to create a seven-episode in-depth tutorial series on how to build a cob house, which can be found on our YouTube channel playlist section. In this video, we'll be briefly covering each step of the building process, which includes building the foundation and earthen floor, making cob, sculpting cob walls, making and applying clay plaster, and building a reciprocal living roof. Before making cob, we first had to build our foundation, and when you build a house with earthen materials, it's important to build strong foundations with adequate drainage and strong roofs with large overhangs to protect the walls. We start our foundation by digging a drainage trench that slips slightly downhill, and we test our trench by pouring water in at the high side. Once we confirm proper drainage, we can then lay the landscaping cloth and fill the trench with compacted gravel. Next, we can stack our stone foundation, which elevates the cob walls off the ground to keep them dry, and also structurally supports the weight of our wall system. With the foundation complete, we were now ready to begin installing our earthen floor. We start by adding a compacted layer of gravel for drainage purposes, and once this is compacted and leveled, we can lay our insulation layer using scrap pieces of cardboard. We apply a layer of clay slip to the cardboard, and then we can begin pouring and leveling our base layer for our earthen floor. For the base layer, we use a mixture of clay, sand, gravel, and straw, and we pour the floor to a depth of about four inches. We continue on with this process, integrating the mix into itself and leveling it out until the base layer is complete. We were now ready to make our first batch of cob, which is created using a mixture of clay, sand, straw, and water. We begin by dry mixing our clay and sand, and then adding water before stomping the mix out with our feet. This method of cob mixing is referred to as the tarp method, and it's the only method we use to build this entire cottage. As you continue adding water to the clay and sand, stomping it out, and rolling it with the tarp, the mix becomes homogenous and begins to form this burrito shape. Once you arrive at the proper consistency, you can then add straw, which helps to provide tensile strength in the wall system. You continue mixing and stomping until the cob is entirely homogenous, and the straw is thoroughly integrated throughout the mix. Lastly, you shape the cob loaves to make transporting and building with cob easier. We apply clay slip to the top of the foundation, and then we begin building our walls by laying cob loaves down and sewing through the mix with our hands to create a You first want to get rid of any seams in the wall, and then work on getting to your desired shape. To transport the cob to the building site, we make a line and toss the cob to one another. We then work as a team to continue integrating and shaping the mix, again with the goal of creating a singular monolithic mass with no seams, and we use a tool called a cobber's thumb to sew through the mix and integrate the layers. As we continue building up more layers of cob, we integrate into the layer below by working through the mix with our hands. Once there is a significant layer of cob on the wall, we can go back and use levels and saws to trim the cob wall into our desired shape. Once we install our door and window frames, the speed that we gain height in our cob walls improves drastically. We continue on making more cob, building up our walls, integrating the layers, and then going back to trim and level the edge of the wall. We shape the cob around our door and window frames, and as we work towards the top of the cob wall, we embed roof tees, which will allow for a structural tie from the roof into the wall system. With our cob walls complete, we were now ready to transition to the sculpting and plastering portion of the build. Using a similar mixture of clay, sand, and straw, we add sculptural details to the cob walls, which really begin to bring the building to a whole new life. We start by moistening the cob walls so that the sculptures can bond to the existing cob, and we build out designs, shapes, animals, niches, and shelves with the sculptural details. We continue shaping the cob around the windows, carving out the niches, and shaping the fine details around bottle bricks. Lastly, we intentionally poke holes in all of the sculptures to make it easier for the plaster to bond during the plastering process. Using various mixes of clay soil, coarse sand, fine sand, and manure, we create and apply test batches of plaster to the wall to see how they would perform. Given the results, we chose to use these ratios for the interior and the exterior plaster. We then broke off into teams to create several batches of plaster before adding all the separate mixes into one bin and giving it a final mix to ensure that the mix was homogenous. To apply the clay plaster, we again moisten the wall with water to create a bond between the cob wall and the plaster, and then we use hawks and trowels to spread and shape the plaster on the wall. We use a collection of rigid and flexible trowels to achieve various finishes, and we also use yogurt lids and spoons for more precision on areas with finer details. We start from the top of the wall and we work our way towards the bottom, continuing to refine the details and the shapes as we work our way down. To achieve a fine finish, we go back and burnish areas that need it to smooth everything out. With the exterior plastering almost complete, we prepare to start applying the interior plaster. For the interior plaster, we repeat the same process of moistening the wall and applying and shaping the clay plaster. On the interior, we use the plaster to smooth out the finishes on our sculptures. We define the shapes around the bottle bricks, and we plaster flush to all of our door and window frames. During this stage of the build, we install tile and marble mosaics, and also finalize the shapes around our niches and shelves. After adding our finishing touches to the interior plaster, we prepare to start building our reciprocal living roof. Earlier in the build, we installed a bond beam that attaches to the roof tees that are embedded in the wall. This system provides a structural tie from the roof into the wall system, and with the bond beam and plastering complete, we were ready to begin installing our rafters. The reciprocal roof is a beautiful and functional roof system in which all of the rafters support one another, requiring no center support to hold the load. For the reciprocal roof, we place the first rafter on the charlie stick, which acts as a temporary support to hold the weight of the roof until the final rafter is installed. We work our way around attaching the rafters with threaded rods and bolts, and once we get to the final rafter, we lift slightly on the rest of the rafters and slide the final rafter into place. Once all the primary rafters are securely installed, we can then remove our charlie stick. We repeat a similar process to install the secondary rafters, which add structural support for our sheathing boards, and then we begin cutting and installing shims to level out the planes of our roof. Once all of the shim boards are installed, our roof is now ready to receive sheathing. We attach our sheathing boards to the shims and rafters, and then we come back with a chalk line to give them all a clean cut. Once the sheathing boards are all complete, we then install our insulation layer using scrap pieces of carpet, followed by our waterproof membrane. To build up the layers of our living roof, we start with a base layer of sand, followed by a layer of straw, and then lastly a layer of local clay soil. To finish the roof, we build drainage downspouts, attach fascia boards, and install a skylight in the center of the roof. We now only had a few things left to do to finish this build. We made a few more batches of cob to finish closing the gap between the top of the cob wall and the roof, and then we made and applied our last batches of clay plaster. To prepare the install for the final layer of the finished earthen floor, we dampen the floor, and then we create our mixture using clay, sand, and manure. We pour the earthen floor mix onto the ground, and then we use screed boards and trowels to level everything out. We continue on going section by section until the earthen floor is complete. For the final step of the build, we install the front door, and then the cob cottage is complete. If you'd like to learn more about how to build a cob house, be sure to check out our full tutorial series, where I go much more in-depth into each stage of the building process. Also, follow us on Instagram at naturalbuildings to keep up with our latest projects.