I did find a problem with building homes out of cob, where to find bulk amounts of clay. I live in tucson / arizona and in the area I'm living in we have very sandy soils and full of low level limestone less then 1 foot under the top soil. Digging threw the limestone is just hell on earth since its so thick petn/hmx is usually used. I did find: http://www.acmesand.com/topsoil/ ("Clay Topsoil") but i cannot vouch for the % clay they are offering as I have never order that product before. Maybe the best option here is to turn a flaw into an asset. /* use the now lose limestone in the cob */
My mission plan is to build low cost /*under 15k for materials*/ rental homes using the round house / concrete floors / reciprocal frame root method.
//700-900 square feet single floor, is there a market for this?;
I do want a cob home to be very fire proof so would sheet metal roof be the best application here? /* what about ferrocement roof?? */
Has anyone built a solar chimney into the house to pull fresh air in and not have to run fans for positive air flow? Air quality is every important so has anyone adding multistage hepa air filters into the house?
About 50 years ago in my area their was a massive tornado, most of san xavier was destroyed, but areas that did take the force were monolithic dome roofs. We all know how very strong monolithic domes are but they are expensive to make because they require an air form and a lot of concrete. Thankfully the area i live does not need high angles on the roof to reduce snow load. What concerns me is a strong concrete monolitic domed roof would be VERY heavy and would crush the cob. Efficiency is necessary /*if a task is too hard your doing it wrong*/ so to keep costs down a better method is needed.
/* mixing cob by machine */
Pug mill "might" not work in my option but an archimedes screw at an angle dropping the cob back into the cob bin might be a good idea. The only problem is I have not found any products on the market that do that. A standard cement mixer could do the job if the cob is mixed wetter and allowed to evaporate at a controlled rate.
/* I plan to make a living out of becoming a landlord. Since I just turned 24 this year it would be a viable investment of my time and money to construct homes for the purpose of being rented. Rental homes are a viable source of passive income that can be done in my spare time. Since cob homes are so hardened from fire/earthquakes/tornadoes would I need to purchase home insurance? I am still not sure if anyone would want to pay 500 usd / for a 900 square foot round house per month. My ideas are very much conflicted. */
Howdy Kraft, welcome to permies. Sounds like a good project. Might be a "low income housing" type of project. I was thinking you could check out a local sand and gravel business for clay. Here is a link to one.