Using Slip-Forms to Make Concrete Walls for Small Buildings

Ken Kern responds to a letter from a concerned reader. In articles from MOTHER EARTH NEWS issue 5 and 6, Kern writes about using slip forms to construct walls.
By Ken Kern
January/February 1972
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Slip forms can be used to build concrete walls.
PHOTO: MOTHER EARTH NEWS STAFF


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Dear MOTHER,

There's more than one way to do most projects, but as an architect I think that some of Ken Kern's building methods are probably a little more complicated and less practical than they might be... especially for the inexperienced builder.

Both the stone wall construction and the compost privy were designed to be built with a "curved concrete slip form." Kern recommends this method for the inexperienced builder, but I feel that it's a difficult one for anyone and probably unnecessary in a small building. Slip forming is generaly used on high rise buildings where it's difficult to build regular form work for buildings that are hundreds of feet tall. But why mix and pour three or four inches of concrete everyday for about 60 days (see slip form detail in No. 6) when the same sort of result can be obtained in two days with conventional methods? In fact, why use curved concrete walls that are only three inches thick as shown on the detail drawings. Six or eight inches is minimum because concrete shrinks as it dries causing cracks, and three inches doesn't leave much thickness after steel reinforcing is placed into the wall (concrete needs steel reinforcing not shown in the drawings).

The thing about recommending concrete walls to inexperienced builders is that there's not much room for learning through mistakes. Once the concrete has set up and hardened, there it stays. The only way to correct or start over is to blow the wall up, beat it to death with a sledge hammer or get a bulldozer.

The waterproofing shown on the stone wall detail in MOTHER NO. 5 is not put to its best use. Actually, it's not even needed above grade or in dry climates and, when it is needed, it should be placed between earth and wall, not inside the wall as shown. Once water gets into the wall, the damage is done, so why protect the concrete? Also, fiberglass insulation shown is a soft porous material which can hold moisture and won't give the stone facing the solid backing it needs for anchorage.

I'm not writing just because I want to nit-pick at someone's good ideas, but because I like what MOTHER is doing... and people with the desire to build on their own need sound practical information if they are to succeed.

Richard Gergel
Rocky River, Ohio


Reading Richard Gergel's letter took me back 20 years, when I decided to replace architectural theory as taught in college for the practical experience gained in construction. I remember the exact instance this metamorphosis took place: a design professor told our class about two women in Ohio who had, almost single-handedly, mixed and slip-formed a two-story 30 by 40-foot double-wall concrete school building. Impossible! Ridiculous! Every architect knows that slip-form techniques are reserved for high rise buildings, hundreds of feet tall . . . as Gergel reminds us.

But at the U of Oregon we were taught to keep open and imaginative minds: we were taught to consider all alternatives however bizarre or unconventional. The photos and description of this school project (as described in the Nov. 15, 1949 issue of THE INTERPRETER) were more than intriguing . . . so I decided to visit the project in person.

Architecturally, the building was rather uninspired. But the slip-forming technique was entirely successful: over 1700 square feet of shell area built entirely by unskilled labor at a cost of $2000. An equal amount was required to completely finish the building.

As it turned out my visit to this Brookville, Ohio, School of Living demonstrated alternative structural techniques . . . but even more importantly, it demonstrated alternative life styles. Mildred Loomis, the school's education director and head slip-form operator exposed me to some of the problems (and solutions) of living that are only now becoming acceptable to more than a handful of fanatic idealists. The School of Living building turned out to be a good demonstration of what can be accomplished by unskilled (female yet!) labor working on minimal budget. It gave me occasion to completely revise my learned facts and opinions as regards architects, building contractors, building inspectors, commercially available tools and materials.

As someone once said, "A little experience disproves a hell of a lot of theory!" If two women can put together a 30 by 40 school building, mixing hundreds of yards of concrete and forming doublethick walls using a simple slip-form, then certainly a man and wife team—-with perhaps a little help from their friends—can erect a simple home shelter.

The concept seemed worthy of further exploration. "Exploration", however, became a formidable endeavor: library research was the simplest part; world-wide travel the most enjoyable; actual on-the-job skill-learning the most time-consuming. It took ten years to get my book, THE OWNER-BUILT HOME, all together and it all started with the simple slip-form. In the final Magnum Opus, however, the slip-form has less than one page coverage out of a total of 300.

That single page represents a trip from Oregon to Ohio, then to Indiana to confer with slip-form inventor John Gieger; a side trip while in Sweden to observe a novel, lowcost sawdust-cement slip-form construction process; an acquaintance with Milton Wend in Massachusetts, who built houses in the 1920's using a modified slip-form method developed by Ernest Flagg; a collaboration with John Magdiel in Los Angeles, who patented an ingenious slip-forming machine. From all this experience and research I was able to devise my own personal brand of slip-forming technique. I found that the slip-form was especially adaptable for building circular structures, using spiral-layered courses swung from a central radius-pole.

So in 1961 my wife, Barbara, and I tried out the spiral slip forming technique on our new homestead. We violated all architectural and engineering precedents but if worked! As our local building inspector cringed and threatened, we created a curvilinear structure with 2-inch thick concrete walls. This first experiment was crude but inexpensive and we raised our family in an atmosphere of freedom from the straight wall and T-square tyranny . . . sans mortgage payment and fire insurance premium. A little experience does disprove a hell of a lot of theory! While Gergel thoughtfully analyzes concrete "control" and thickness and reinforcement "requirement", we happily enjoy our debt-free house.

In conclusion, I have only to add one note of explanation for this verbose reply. Dozens of establishment architects and contractors have purchased my book, but they are usually discreet as regards any specific critical evaluation. I accept—even welcome—constructive discussion on any objective, technical aspect. But when I compare my own limited college-trained knowledge against the years of accumulated building experience of such giants as Gieger, Magdiel, Wend, and Flagg . . . then the whole scene becomes rather ridiculous.

The slip-form is personal to me: by way of this tool I was introduced to the School of Living and to some very close building associates. The slip-form made possible the walls that housed our growing family. In short it symbolizes all that is possible and significant and worthwhile for the unskilled and the poor house-needy families throughout the world.

Ken Kern
Oakhurst, Ca.


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