Sharing information and promoting earthbag building
a Review by Kelly Hart
I have been anxiously awaiting my review copy of Earthbag Building: The Tools, Tricks and Techniques by Kaki Hunter and Donald Kiffmeyer for quite some time, and am pleased to now have the chance to review it. Published by New Society Publishers, this book should find wide distribution and many fascinated readers. Having built my own home using earthbags, I have a fondness for this method of building and am a proponent of its use.
I applaud the authors and the publisher on the creation of a well organized, clearly written, lavishly illustrated and useful how-to book on the subject of earthbag building. They state the significant reasons for considering this technology, and then proceed to lead the reader through the basic steps of building this way. They write with well-grounded understanding of the physics and geometry of the subject as well as good humor. As they say in their Introduction, "The focus of this book is on sharing our repertoire of tools, tricks, and techniques that we have learned through trial and error, from friends, workshop participants, curious onlookers, ancient Indian nature spirits, and smartass apprentices who have all helped us turn a bag of dirt into a precision wall-building system that alerts the novice and the experienced builder alike to the creative potential within themselves and the very earth beneath their feet."
Doni and Kaki (as many of us know them) came to earthbag building via a workshop with Nader Khalili of The California Institute of Earth Art and Architecture, who is the father of modern earthbag works; he calls the technique Super Adobe. This fact is key to how the authors relate to earthbag building: as far as they (and Nader Khalili) are concerned, the bag itself is merely a form into which adobe soil is placed and allowed to cure into a hard, solid earthen block, which then becomes part of a structure. Ultimately, the bags themselves are not considered to be structural only the solid adobe within them. The initial chapter that describes appropriate materials for earthbag building goes into how to find or prepare the right mixture of sand and clay to make good adobe soil to fill the bags. The tools and tricks that they describe all follow from the intention of using adobe soil as the basis for building.
This approach to earthbag construction clearly produces extremely solid, durable, natural, sustainable and lovely structures, but it limits earthbag technology to a subset of "earthen architecture," that includes adobe, cob and rammed earth it becomes just another way to build with earth. From my experience, I know that earthbag building can be much more than this! For instance, I built my earthbag home by filling the bags with crushed volcanic rock (scoria), which has the huge advantage of being an insulating material. I know of others who have filled the bags with rice hulls, another natural insulating material. Doni and Kaki state that, "Filling the bags with pumice alone produces a lumpy bag full of loose material that refuses to compact while lacking the weight that we rely on for gravity to hold it in place. We prefer to maintain the structural integrity of the wall system first, and then figure out ways to address insulating options."
Actually, lumpy bags are of no consequence, since they all get plastered anyway. Weight can be both an advantage and a disadvantage in a building system, since heavier objects produce more disruptive forces whenever there is any imbalance; even though gravity tends to hold things down to earth, it can also bring things down to earth. The real question is, does the wall system tend to hold together under all conditions that it will likely encounter? From my experience with earthbags filled with light scoria and plastered with wire mesh reinforced papercrete, the answer to this question is a resounding YES. In fact I once did an experiment of undermining a 12 foot section of such a wall by digging out the earth from beneath it to such an extent that the entire wall was resting on a tiny 6 inch pedestal in the middle, while most of the wall was totally suspended in mid air, and it held together without any deformation at all! Could any earthen wall systems withstand this test? (Pictures and a description of this experiment can be found at here.)
The methods for insulating earthbag walls that are suggested in Earthbag Building lack the elegance of simply filling the bags with insulating material in the first place. As far as I am concerned, one of the true merits of earthbag building that is not duplicated by any other wall system is the fact that the bags can be filled with a wide range of materials, according the their availability and function within the design of the structure. While loose material does not compact and solidify in the same way that adobe soil does, it will compact sufficiently to remain static in the wall, at least until both sides of the bags are plastered, at which point the wall ideally becomes monolithic. The only exception to this that I have experienced is with filling the bags with very fine, slippery sand, which does tend to shape-shift in the bag. The same principle that makes structural insulated panels (SIPs) so amazingly strong is at work here: a soft core of insulation is clad with tough skins of tensile material, and you can build whole houses with them with hardly any other framing.
Earthbag Building provides a good foundation for the basic concepts of building this way, starting with the foundation itself, and proceeding on to examine appropriate design features for walls. The merit of curved walls is clearly stated, as is the need for buttressing straight wall sections. The placement of barbed wire between the courses and how to keep it from being too unruly is covered. How to build corners, columns, door and window openings are all clearly shown. Even ideas for incorporating post and beam framing into an earthbag wall is discussed. I am particularly impressed with their use of "Velcro plates" of spiked wood inserted between the bags as a way to anchor door frames or other wall attachments. Also their use of wire mesh "cradles" where the bag ends are exposed, as under arches, makes a lot of sense for giving the eventual plaster something to hang on to. There are chapters on exterior and interior plasters, which they have much experience with and have many useful tips and recipes to reveal. There is a short chapter on poured adobe or rammed earth floors.
There is a whole chapter outlining a variety of roof systems that can be integrated into an earthbag structure but, Doni and Kaki claim that domes are "where earthbags exhibit their greatest potential; to us, it is the essence of earthbag building. We are able to build an entire house from foundation to walls to roof using one system." I agree with them about this. The physics and geometry of dome building is well covered. They provide a step-by-step illustrated guide to how they built their 12 foot interior diameter "Honey House" dome.
When I compare my own experience of building my earthbag house with what is presented in this book, I would say that for the most part it is similar, but there are some significant differences. There is a degree of precision advocated by the authors that seems excessive to me. For instance, they use a fairly elaborate compass arrangement for placing the earthbags in circular or domed structures that assures a refinement that ultimately is a matter of aesthetics, not structural necessity; I accomplished the same measurements with either a piece of string or a length of pipe. All of this precision takes time, which at least partly accounts for the fact that they suggest that on average one trained person can fill and lay only four bags in one hour. I easily proceeded at twice this rate, working by myself, but this is also because the bags of scoria only weigh about 35 lbs each, so they can be quickly filled on the ground, carried to their location on the wall, put into place without the need of metal sliders, and tamped tight with a few slams of a large steel tamper, and then it is on to the next bag. Laying earthbags filled with adobe in the manner described in this book would be extremely cumbersome, if not impossible, by one person; they recommend crews of at least three people.
In the end the reader is given a wealth of information, gleaned from the authors' hard experience, in a manner that is quite readable and clearly illustrated. I can recommend Earthbag Building for anyone thinking about building this way, as long as the perspective is taken that what they present is only one of many ways that earthbags might be utilized for construction.
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