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TECHNICAL CONCEPTS, TESTING, TECHNIQUES
by Jeff Ruppert, P.E., Odisea Engineering, Planning and Design, Boulder, Colorado A wide range of topics at this year's International Straw Bale Conference contributed to its continuing role as a keystone to our movement. Topics ranged from open bamboo construction to hemp, interspersed with open forums with wide participation. Owner/builders were eager to share their experiences, both good and bad. Being a scientist of sorts, I was most interested in a few more technical concepts that promise to play a large role in future straw bale construction. Beginning with an interesting concept which I think has the most potential to be implemented on a large scale immediately. Chris Magwood's concept of stacking the walls without openings (aside from one door) in either post-and-beam or loadbearing construction, running the wiring, lathing and plastering, and once plastered with two coats, cutting the window and door openings out, inserting window bucks, lath and plaster to the cuts and moving on. It goes without saying, there may be some unforseen issues that arise, but I believe they are not important enough to warrant not using this process. With some forethought, as is the usual part of the construction process, we can work the kinks out and be able to construct buildings faster, easier and stronger. I would like to go one step further and describe some of the first thoughts that have come to mind while pondering this shift. First, as a residential contractor and engineer, I tend to appreciate the virtues of a more efficient system. Stacking the bales with fewer interruptions will save a tremendous amount of time and energy. Take for example a typical straw bale wall system. At $20 per square foot of wall, over two-thirds of this cost is labor, and over two-thirds of that cost can be attributed to plaster and plaster preparation. Lathing joints between materials is incredibly time consuming. By reducing the extent of it by lightly lathing the windows in after plastering, a significant amount of time, and therefore money, can be saved. Secondly, and just as important a reason for using this process, is strength of the wall. All of the interruptions by openings, along with framework, can reduce the amount of straw you have in the walls to nothing in spots. By not having to place and prepare so many members before plastering, the plaster has more straw to adhere to. Once cut, doors and windows can be framed with a variety of buck systems, from light weight to stiff and strong. A third reason in support of this process is also related to strength. You get your main structure before placing windows and doors. Movement by the building will be minimal once plastered. There are actually more advantages to using this process - something for everyone to think about. Another idea, more affirmed than invented, also brought up by Chris Magwood, was the idea of stacking bales on edge in a loadbearing situation. Chris remarked on their success, without problems, at being able to cut up to four strings before plastering, in order to cut in a nicho. My experience with bales has been similar. We sometimes do not realize how compact and stable bales are in a wall configuration. Once confined, they do not tend to squirt out of the walls as we may tend to think. Since the loadbearing capacity of a finished bale wall is in the plaster, the only issue with strength would be the bond of the plaster to the different sides of the bale. I believe this can be overcome - another topic for future discussion. And there was the ever and omni-present discussions of lime plaster. Bruce King (P.E., EcoBuilding Network, California, and author of the book Buildings of Earth and Straw, another suggested reading) shared some very interesting information about strengths and qualities. For example, mixing lime with soil may not be as good a recipe as we may think due to what type of lime we use. Most of the lime used has a significant amount of impurities present in the original limestone, called hydraulic lime. This is opposed to more pure lime called dolomitic lime. By virtue of the impurities, these two types of lime set up within a pozzolanic (hardening) reaction with clays and sand in widely varying rates. However, even though the setting process may be elongated, the desired strength may eventually be achieved. This means, if we plan for a stronger plaster down the road, it can work - just be aware of what you are using. There were actually so many topics I could never cover them all in this report and space. I can only encourage everyone to attend the next conference - time, date and place to be determined. It is always a wonderful experience to spend time, learn and share information with the founders and leaders of the straw bale movement. Jeff Ruppert's e-mail address is jruppert2@uswest.net. Or he can be reached at Odisea Engineering, Planning & Design, 2814 15th St., Boulder CO 80304. |