Ferrocement

Ferrocement is a composite material which is used in building or sculpture with cement, sand, water and wire or mesh material—often called a thin shell in North America.

Ferrocement has great strength and economy. It is fireproof, earthquake safe and does not rust, rot or blow down in storms. It has a broad range of applications which include home building, creating sculptures, repair of existing artifacts and building boats and ships.

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Construction

The desired shape may be built from a multi-layered construction of chicken wire, and if needed reinforced with steel wire or steel bars. Over this finished framework, an appropriate mixture of cement, sand and water is spread out. During hardening, the ferrocement is kept moist, to ensure the cement is able to set and harden.

The wall thickness of ferrocement constructions lies in general between 10 and 30 mm. Like other applications of cement, a considerable amount of time may be necessary for the material to fully cure and reach its final strength. Curing time is dependent upon the span or application load, and ferrocement can take a month before it is ready for use.

One who wishes to accomplish a smooth, finished surface will find that 10 - 30 millimeters is a highly technical and extremely difficult task suitable only for boats or small sculptures. Ten millimeters is nearly impossible unless one has a laboratory or supporting molds. Robert Maillart's beautiful ferrocement bridges are approximately 200 millimeters thick, for example.

There are at least two reasons why sculptors and builders who build for the long term avoid zinc coated wire such as poultry netting. 1) Galvanized steel used for animal cages is not required to be high quality steel. 2) Zinc is similar to copper chemically; it disolves slowly in the concrete matrix. Ferrocement artifacts utilizing zinc within the concrete matrix are only acceptable for the short time horizon of modern buildings or boat hulls. Sculptors and builders who build for a future of many centuries use uncoated high quality steel. A small quantity of galvanized wire is not harmful as the outer armature layer to hold fresh plaster in place.

Economics

The economic advantage of ferrocement structures is they pay for themselves. Houses pay for themselves with almost zero maintenance and insurance requirements. Water tanks pay for themselves by not being replaced periodically.

A ferrocement structure which encloses above 50 cubic meters is economically superior to almost any building material. This figure has not changed since Robert Mailart used it to economic advantage circa 1900.

Application

In India, ferrocement is used often because the constructions made from it are better resistant against earthquakes.

In the 1970s, designers adapted their yacht designs to the then very popular backyard building scheme of building a boat using ferrocement. Its big attraction was that, for minimum outlay and costs, a reasonable application of skill, an amateur could construct a smooth, strong and substantial yacht hull.

Advantages

The advantages of a well built ferrocement construction are the low weight, maintenance costs and long lifetime in comparison with steel constructions. However, meticulous building precision is considered crucial here. Especially with respect to the cement composition and the way in which it is applied in and on the framework.

When a ferrocement sheet is mechanically overloaded, it will tend to fold instead of crack or rupture. The wire framework will hold the pieces together, which in some applications (boat hull, ceiling, roof) is an advantage.

A ferrocement construction has 10 to 25% of the weight of a comparable construction made of bricks.

Another important advantage is the ease of construction. Concrete is referred to as "mud," in central north America. People have been building with mud and sticks since moving out of caves. An armature of reinforcing steel and wire replaced organic reinforcing material during the industrial revolution.

Disadvantages

The disadvantage of ferrocement constructions is the labor intensive nature of it, which makes it expensive for industrial application in the western world.

This "disadvantage" is the primary advantage for those who compete with western world corporations. High labor content fosters small-scale enterprises by employing low-cost marginal labor to fabricate artifacts which require large labor inputs. When large industrial corporations are outside their own economic system they must compete directly without government protection. Highly motivated ferrocement entrepreneurs build aqueducts, drainage systems, water and septic tanks, large flower pots for hotels and parks, water troughs, shade roofs, small houses, etc.

• Ferrocement Educational Network

• Flying Concrete Steve Kornher's light weight concrete structural & sculptural forms

• Water Storage book by Art Ludwig, includes Ferrocement Tanks & Excel Water Tank Calculator

• Wood Family: How to build a ferrocement boat