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Ferrocement Construction Philosophy
Comprehension begins with vision. An encyclopedia, for example, attempts to include the full extent of human awareness; encyclopedic is comprehensive. Human awareness is expanding so fast it is only matched by the big bang bloom itself (see Brian Green's writings, for example).
Examination which probes the tiny realms quickly encounters complexity and variation equal to that found in the gigantic direction. To comprehend concrete, think about the crystal intricacies of snow flakes. Shrink a thousand times smaller, inside concrete, and you will see molecular structures with straight spines entangled, like hair brushes with the bristles poked into each other. An entangled mass of giant sea urchins is very close to the sight which a person small enough to walk among the crystal spines would see.
The crystalline spines of concrete grow for an extended time period, perhaps fifty years in ideal conditions. Concrete molecular growth requires water. Twenty-eight moist days is considered the optimum time period to grow concrete structures which are nearly perfect. Heat speeds the process, cold slows it. If the material becomes dry, then the molecular process we perceive as hardening is halted. Hardening cannot be restarted after it has stopped. It is easy to see the changed character of the concrete after it has been allowed to dry; the concrete does not absorb water, it becomes waterproof.
Ferrocement is standard cement, usually mixed with plaster sand. Ferrocement is also written as ferrociment (french), ferrozement (german), ferrocemento (italian and spanish), and ferrocimento (portuguese).
Concrete, bamboo and steel all expand and contract equally with temperature change. Concrete reinforced uniformly with small fibers and wires can flex under physical strain approximately equal to expansion or contraction due to temperature change. Increasing uniformity of reinforcement throughout the matrix is the direction toward ideal ferrocement. This is so because increasing perfection of reinforcement dispersion creates a matrix which transmits stress forces uniformly. When crystal motion is induced by stress rather than temperature change and the molecular stress distance is less than that caused by temperature change, concrete becomes as flexible as fiberglass and resin, with a modulas of elasticity identical to the third decimal place.
A tangential subject, heat gradient, reveals the limit of this analysis. Concrete which is expanded from heat on one surface and shrunk from cold on the other has a temperature gradient from one side to the other. If that gradient is too large, the concrete will slowly shatter into multiple striations and eventually turn to powder. That's why a heated ferrocement structure in a freezing climate must be isolated from the climate with insulation. The ferrocement mass inside an insulation shell also moderates temperature swings, this adds noticeably to comfort.
Ferrocement is sometimes called, "thin shell concrete." Though this name is descriptive, it can cause translation and technical difficulties internationally. "Thin" also refers to paint, clouds, soup . "Structural shell" is a specific word in many languages. To understand how words get mixed up between languages, think of this; pouring rain is, "cats and dogs" (English), heavy spanish rain is called "planter pots." Ferrocement descriptors have varied over the years. "The thin shell", does work as a description, yet it is important to avoid misunderstandings caused by using several words to describe the same thing. International understanding is found on many paths and dictionaries are often the maps.
Construction
These mixing proportions are measured dry. Three sand and one cement, written as 3:1 (three - one) and (3 - 1). 2.5:1 is very rich, above 3:1 is less so. There are few areas of the world where these ratios do not apply.
The core of ferrocement is the Armature. Always test and cure an example mortar mix prior to concrete application on valuable armatures. There are at least two regions that have cement of possible bad quality. Northeast America and the Philippine area of the pacific southwest. Do not plaster a valuable armature in those regions without a test. Hard concrete makes a sharp sound on impact. Soft concrete makes a soft sound on impact, it's like soft sandstone; no ring to it. Engineering tables of hardness are a number representation of this acoustic phenomenon.
The heavier reinforcing steel shown in the illustration is often not necessary once the structure is complete. The internal steel in those situations is what holds the armature during construction.
Ferrocement thickness is determined by what is built. A movie set, for example may be as thin as window screen or burlap painted with cement slurry. A major bridge will be 15 - 30 centimeters thick (6 - 12").
Ferrocement is a composite matrix of steel or biological fibers in concrete. Fiber glass and resin is also a composite. Both composites have approximately equal elasticity. Ferrocement can become a canoe, drum or bridge. Many universities compete every year to build a ferrocement kayak, this competition has happened for many years. Ferrocement is best for sculpture, reservoirs, houses, bridges, and repairs.
Add water until the consistency is such that a line drawn with the index finger slightly settles slowly. Draw the line on the surface of fresh mortar, make it 2 - 3 centimeters deep (1"±). Examine the speed and fluidity of collapse along the line, also known as "slump." It should relax toward rounded edges. Water used excessively limits strength. If the mix is excessively fluid, add measured dry sand and cement.
Advantages
The primary advantage of ferrocement constructions is that they pay for themselves. This results from almost zero maintenance and insurance requirements. Understanding ferrocement longevity leads to profound insights. Consider a society in which housing pays for itself. Now consider the economic and cultural effects of housing which pays for itself, especially within an economy where home rentals are a large fraction of the national economy. The greatest advantage of ferrocement over standard construction is that the homeless can have their own homes. And, as one famous philosopher said, "It's easy."
Another important advantage is ease of construction. A novice will have difficulty making the artifact look professionally perfect, yet it will be very strong. Concrete is called "mud" among building professionals. Mud is easy; 85 - 90 percent of the total cost is labor. People have been building with mud and sticks since moving out of caves. It's easy.
Notice that labor intensive work is perfect for small businesses competing with large corporations which cannot afford to pay sufficient wages and still make a profit. Only one worker per family was needed before large corporations provided such a large percentage of total employment, now at least two are required. Labor intensive ferrocement constructions help reverse this trend.
As global warming accelerates, a search for alternatives to the system which is injurious to our planet will become more urgent. Labor intensive work and artifact longevity will become major considerations in all economic equations. Labor intensive work helps more families find meaningful work. Jobs which create something that pays for itself are the kind that heal the planet and build strong communities.
Ferrocement is among few construction technologies which lead to such profound economic and social conclusions. Bamboo is another.
Note: Insights gained through the looking glasses of bamboo and ferrocement have not revealed an end of corporations or governments. Corporatism, however, as communism before it, does not fly or hold water.*
*ferrocement economics, macro section