Owner-Built Home & Homestead
(Page 13 of 15)
The first step in erecting a corrugated shell structure is to install the "falsework." This usually consists of tubular steel or wood-truss ribs, placed on 3-foot to 8-foot spans (depending upon the span of the arch). This formwork can be kept very light. Between each rib a vegetable fabric is laid, such as hessian, jute, coir, sisal or burlap (it was found that, whether stresses are due to static, dynamic or thermal loads, vegetable fabric has the remarkable property of resisting high tensile stresses in all directions).
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Dr. Billig says:
". . . the dry hessian is stretched by hand as tightly as possible over the rigid falsework and securely fastened to it. By shrinking the fabric with water the fibres are stretched still tighter, and in this state they are covered with a cement slurry by a brush. The cement is carried into the pores of the material where it remains. It maintains the shrinkage of the material, and the initial tension is maintained as a permanent tension in the jute after the concrete has set and hardened."
Absolutely no metal reinforcement need be used in corrugated concrete shell roofs, foundations, or floors. The shell is less than 2 inches thick, with spans up to 60 feet. A day after the last plaster coat is applied the falsework can be removed, and the structure will then withstand 85 miles per hour winds.
In excessively hot or cold regions it may be desirable to build doubleskin shells. This simply involves placing another layer of fabric over mortar fillets (or over a layer of bricks), and then plastering as before. This cavity air space improves the insulating qualities considerably (U factor, 0.37). In the tropics it was noted that as the air of the inter-shell cavity became warmed from the day's heat outside, it rose along the intrados of the arch, collected more heat from the upper regions of the shell, and then escaped through vents placed along the crown. The result was an effective natural ventilation system as well as efficient heat insulation.
Like Billig of India, Jack Bays of Cedaredge, Colo., is an old-timer in the low-cost composite building field. For 25 years he has directed an experimental housing laboratory in Oklahoma City. His many building material formulas are interesting—and in some cases valuable—but hardly worth his expensive "schooling" program required to come by them.
Bays' material consists of 12 quarts of asphalt emulsion, 8 lbs. of paper and cardboard run through a farm hammer mill, and 12 gal. of clay and water mixed in equal parts. The finished product, called "Rub-R-Slate" can be troweled or sprayed on walls or floors. His favorite RRS construction method consists of wall studs spaced on 30-inch centers, chicken wire spread inside and out and tacked to the studs, the inside stuffed with straw to form a base for the RRS and to act as deadair insulation, and then RRS solution plastered on both inside and outside walls.
A two-bedroom home in Oklahoma was recently built for $1200 with Bays' materials. The walls consisted of used quart oil cans, braced by horizontal wires spaced every two feet around corner angle-irons and braced up with a mortar of clayey sand, asphalt emulsion and water. The RRS coating was applied both inside and outside.
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