Owner-Built Home & Homestead
(Page 12 of 15)
In the Eastern part of the country, expanded slag is available for lightweight concrete aggregate, as well as vermiculite. In the West, pumice is perhaps the most popular and least expensive of all lightweight aggregates. Scoria and perlite, also of volcanic glass composition, are readily available. One major advantage of a lightweight aggregate is in the reduction of structural weight (its use may reduce the dead load of concrete itself by more than one-third). Also, the thermal (as previously stated) and acoustical insulation values of lightweight aggregate are many times greater than those of standard concrete.
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Reference was made in a previous chapter to the poured stone rubble technique developed by architect Ernest Flagg. Another contribution made by Flagg to owner-builder housing was a way of building non-bearing partition walls out of wire lath and plaster. His system is most interesting. Two plasterers, one on each side of a single layer of wire lath stretched from floor to ceiling, trowel against each other. After the first coat, the wall is sufficiently strong for a finish layer to be applied without back support. The actual strength of reinforced plaster is astonishingly high (it is not unusual to find a plastered wall holding up a roof after the rest of the wall has been destroyed by fire).
Actually in 1930, Major deW. Walker (of Ireland) found that plastered fiberconcrete will support 600 lbs. per square foot. On this basis, he developed a new method of strengthening concrete, called "No Fango." The process is simple. Fiber reinforcement is spread lightly over a framework of wood, reinforced concrete or steel, and the material is then allowed to shrink. While in this stage it is thoroughly impregnated with common cement; and concrete is then applied in the form of plaster. The finished wall is one-inch thick; for outside walls an air space is provided between two one-inch layers.
This same idea of "starched concrete" inspired some experiments by Bernard Maybeck, renowned San Francisco architect, in building his own home. A framework was set up and wires were stretched around it 18 inches apart. Burlap sacks were soaked in a mixture of portland cement and powdered lightweight aggregate, made very thin with water. The bags were then hung on the wires like clothes on a line, and a sturdy, low cost, fireproof wall resulted.
Obviously, the very nature of fiber-concrete construction demands equally unique structural form and design practices. In the early 1950's, Dr. Kurt Billig (the very able director of building research, Central Building Research Institute, New Delhi, India) evolved a totally new building form using starched concrete. A house he displayed at the 1954 International Exhibition on Low Cost Housing (New Delhi) was a simple corrugated shell. Here, for the first time, a house was developed for that 90% of the population of India that cannot afford to pay for even a minimum-priced conventional structure. The CBRI shell house contained one-sixth the volume of building materials that would have been required for a conventional brick house of the same floor area, and also cost about one-sixth as much to build (where 313 man-days would be required to build the conventional brick house, only 118 were required on the corrugated shell house.)
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