I am working on a grant for an organic farm school that I work at near St. Louis, MO to build a cob garden tool shed 12'x 12'. Unfortunately due to time constraints I am not finding the information I need quickly. I need to find out the ratios of sand, clay, straw and water to build a cob shed of this size. I need to know amounts that should be used for a shed this size. The idea is that it would have a large overhanging roof to cover a vegetable washing station. It would have running water, and the roof would be for water catchment as well.
The initial information that I have is that the sand:clay ratio is 3:1. However I am still needing to know the amount of straw. For this size building I have listed as 30 tons of sand, 10 tons of clay, and 13 tons of gravel for the foundation. I need to know how much wood, and of what sizes, etc... so that I can price that out as well. This would include one door, and one window. I have the costs for both of those.
If anyone can help me please contact me as soon as possible!
Hi! The reason Jeff posted the book and the calculator is because the ratio of clay to sand to straw depends on how much is present in the soil you are using. The Hand-sculpted House does contain a 3:1 ratio for sand and clay, but, if I remember correctly, it is only one of 3 or 4 ratios that have been used all depending on the makeup of the soil, what the climate is like, and the purpose of the cob being made.
I'm afraid cob building is not a spur of the moment project; it requires some forethought, and calculation. If you read The Hand-Sculpted House you will know why. I found it a fun and interesting book to read.
BTW, if you do by some chance find someone who gives you a ratio for straw, BEWARE! That 3:1 ratio may not be what you need and may result in your shed falling in on itself.
Because I do not work in "mud" as a primary focus, and because I have real concerns with many of the "earth based," structures I see rapidly growing in popularity, I was not sure how to respond to this post.
Jeff S. did the best of all thus far, (bravo Jeff.) My focus has always been on the more traditional applications of "earth architecture," and what often concerns me is the recommendation folks make (and I have made in the past) about "mix ratios." There is just so much more to it than that. Clay type, aggarget type, fiber type, etc. all effect the matrix you are trying to achieve, and we haven't even discussed the design application of the architecture yet. I am not worried about building falling down and hurting folks (yet) but very concerned that too many DYIers are jumping into this earth architecture thinking it is just a simple process of digging up some clay mud, following what appears to be simple directions, and building a wall for their project, (which is actually how I have heard several folks describe the process!) In many ways it is simple, but that misconception could (is?) leading this craft down some rabbit holes that I worry me about architectural endurance and ultimately safety.
Please read as many books on this subject as you can, and if at all possible, take a workshop from a "seasoned mudder" that has at least 10 years of experience designing, and facilitating successful earth architecture. I have been in the traditional building arts for over thirty five years, and I would not tackle one of these "full mud" structures without a co-facilitator of that experience level.