Q: the obvious question is: what IS cob and how is it possible that it can withstand heat and moisture?
David: Cob is a very ancient medium used to build homes and structures, it consists of a mixture of clay, sand and straw. The earliest use of cob can be traced back to Yemen and the city of Shibam which is called the Manhattan of the desert in terms of age, Shibam is mentioned in the bible. It was used throughout the UK in many a regal homestead and can still be found there today as it has had an explosion in rebirth.
The ingredients are as important as those of any creation, the clay must be very sticky and thick, preferably local to the build site, the sand must have a rough silica content as this helps the sand particles lock together as opposed to a smooth silica content which will roll apart like stacking marbles into a pile. The straw must be clean straw with very little moisture content, preferably just turned from green to tan. The straw acts the same to cob as rebar acts to concrete: it gives it tensile strength as well as lateral strength. When compared to the strength of concrete, on the Newton scale concrete rates at 2-3 Newtons, cob rates at 1-2 Newtons. Obviously not as strong as concrete but pretty close for a sustainable medium. It is this slight difference that allows cob to stay more flexible as opposed to concrete in an event such as an earthquake or floods.
The heat resilience is based on the natural resistance of earth to burn. This kind of works the opposite for thermal gain, the mass of the walls in conjunction with the sun helps to absorb and hold in the heat on cold days and then repel the heat on hot days. With cob ovens, this is the perfect effect. Heat the cob up and it holds the heat for hours. Moisture is only an issue if it is allowed to be present or to penetrate the cob. Typically a water repellent ingredient is used to prevent moisture penetration; lime is the preferred natural moisture blocker, and this, added into an earthen plaster will prevent water from infiltrating the cob and the more layers you do almost guarantees it.
Q: is the cob oven built differently than a cob house?
David: In ingredients no, in build yes. In a cob oven there is need for specific functionality so the way an oven is built can vary from a home in a couple different ways. The oven needs to retain as much heat as possible so the structure is layered to allow this more efficiently. In a home a mixture of cob is made then applied in a thickness typical of 16-18 inches, in a cob oven the thickness is typical of 6-8 inches. Then of course the home has framing aspects as well at windows and doors.
Q: when and how did you get interested in building with cob?
David: I have always been intrigued by building methods such as Log Homes, Yurts, Tipi's and even Subterranean homes, but after being introduced to a more sustainable and earth connected type of building I realized my spirit was trying to reach me in any way it could and it used those building methods as a primer of sorts. I lived with a communal group in Florida, learning to eat better and communicate in truth as well as living and growing in a large group of people all with their own hang ups but united in our effort to drop the societal learned lies and be real with each other. We built housing structures on the 16 acres of land we lived on using reclaimed materials from abandoned drug houses in the nearby city, we would form "demo crews" and go demolish a home for the materials as per agreements made with the home owners. This was my first lesson in reclaimed building and communal living.
I was first introduced to cob as a application to straw bale about 3 years ago. I took a straw bale class in Butler, Tx. from a natural builder named Nick Moser, I learned how to build a straw bale home from the ground up, this woke me up to the possibilities of natural building.
1/4 turn spiral stair designed by David for Dr. Craig Sommers
new cob home
I scoured the net for information on as many topics as I could find. After learning what I could and attending some webinars and seminars, I was asked to come help a guy in Bastrop named Dr. Craig Sommers, frame in the second story of his cob home; we had been introduced by Gayle Borst of Design Build Live out of Austin Texas. I live in Houston and you have to understand this town is not like other towns in Texas, it is very money and fashion and oil based, there are people here that want to build naturally but the odds, as well as building code are really high against it. I called around to try and find any natural building groups in my area and found none, there are a couple great permaculture groups, ( I wanna thank those guys at Last Organic Outpost ) and Dan Phillips wonderful work, but nothing geared towards natural earthen building.) Gayle and I had emailed back and forth about the possibility of starting some type of group here in the Houston area, and passed on the contact with Craig.
I was thrilled to be able to be part of a full cob home build workshop, I spent 37 days at Craig's place and learned a lot about what it takes to live sustainable. I converted to vegetarianism while there, I, along with a couple other people, built this home by sinking cedar tree trunks into the ground for corner posts, framing up his window and door bucks, rebuilding some old doors he reclaimed, and framing up his second story to prepare for the first floor cobbing. Christina Ott from Barefoot Builder came to teach the cob workshop for a 7 day course, this woman is a gold mine of natural building knowledge as well as a powerful spirit. She is also going to be our instructor for the 10 day owner builder workshop in October at our place in Hempstead.
The connections and friendships I have made since beginning all of this has been extraordinary to say the least. The opportunities to further my skills also have been presenting themselves in ways I would never have noticed before. I am glad for this type of lifestyle as it is allowing me to truly give my children a solid and secure future here on this planet, in truth they are my driving force, and teaching them to live in connection with this planet and the nature on it and building beautifully sculptured homes for them to live in as well as the knowledge of how to do it themselves is by far more in line with the responsibility of a parent and friend and a human.
I asked David to share what current projects he is working on. Here is his reply:
1) Building my own website (New Jura Building) based solely on natural building and not just off grid living as is the forums main focus.
2) Design and consultation with John Matznick of GreenTechFusion on a couple of sustainable container homes he has planned for the Conroe area. I have submitted some simple designs based on his and his wife's ideas and they are in the process of submittal for permits. I will be doing some of the hands on build with John and teaching some unskilled college persons how to frame up these builds, and to utilize and install rainwater catchment, grey water diversion and reuse, and maybe some composting toilets but I am not sure about the latter.
3) I am also working with Kevin Rowell of The Natural Builders, as well as many other natural builders to create a volume of downloadable PDF's based on natural building building techniques drawn or illustrated in step by step form to be able to empower the builder and non builder alike. Conventional building has its technical manuals and they are very hard to read for the lay person, we are trying to come up with one for the natural building process that is easy to read, understand and easy to follow so that anyone may instantly see the steps necessary to build their own whatever even if they don't speak English.
4) I have the cob oven with you guys March 28th
5) April-May I will be attending the Mariposa Ecovillage in Amarillo Tx. for 2 months of a 6 month Natural Building Summer Camp where,"we will craft a village of nine eco-cabins of various methods and materials to act as mini-model homes and lodge where people can stay when they come to visit the ecovillage, or if they are interested in natural building and just want to experience staying in one. To facilitate the construction of these demonstration units we are putting together a "Natural Building Summer Camp", bringing together paying workshop participants, work-trade apprentices and expert teachers for an extended learning experiment combining the best aspects of a fully supported multi-project building site and a community workshop environment."
This event is sure to be a blast as I will be heading the woodworking teams for a couple of the build groups in this summer camp.
6) June I will be back in Hempstead were I will be hosting some work traders to come live on my land and help get it in the necessary shape it needs to be in to host the 10 day owner builder cob workshop in October. We will be building a 4 person composting toilet house made from re-purposed wood pallets, a shower house also made from wood pallets and finally a workshop kitchen house also from pallets. We will then install the recycled urbanite stem walls in preparation for the cob walls to go in, and install the round wood timber framing for the roof structure.
As you can see, David is passionate and fully committed to learning as well as teaching others about self sustainable living. Thank you David, it is inspiring to learn more and see what one man can do! We look forward to meeting you when you come to The Bone House in March. You can find out even more about self sustainable living on David's Off Grid Homesteading Forum.