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The term ‘ferrocement’ refers to cement reinforced with some sort of steel, be it thin wire, wire mesh or thicker reinforcement bars. Cement is great in withstanding pressure, but not very good in withstanding tension forces. For steel wire it's exactly the reverse. A combination of the two yields an excellent construction material, which does not rust, rot or blow down in storms. Ferrocement is different from ordinary reinforced cement in that a lot more steel is used, along with a strong cement mixture. This leads to lightweight structures which can have almost any shape.
[[Image:shelter.jpg|thumb|center|300px|A shelter at an orphanage in Rwanda, made with ferrocement and bamboo. Photo [http://www.ferrocement.com/Shelter-2009/6-26-09-shelter.html ferrocement.com.]]]
====Boats, houses, statues====
====Water tanks====
Back to water tanks. Say, you need a 2 m<sup>2</sup> ferrocement water tank for your [http://www.akvo.org/blog/?p=813 rainwater harvesting system]. The classical technique is to start with building a [http://vimeo.com/8367598 cage of steel reinforcement bars], covered with chicken wire mesh. An alternative is to start with an [http://vimeo.com/channels/emas#8453558 inner form of metal sheets], which is later removed. Or, for smaller tanks, a sack filled with sand is used. Once this structure is established, a cement mixture is applied. As ferrocement is much stronger than masonry, the thickness of the walls is in the range of 10-30mm. During curing (at least 10 days, although 30 is better) the cement is kept wet and wrapped in plastic sheet. Fill’r up, and enjoy.
[[Image:akkerman.jpg|thumb|center|300px|A ferrocement tank under construction in Guinea-Bissau. Photo: [http://www.degevuldewaterkruik.nl/ Paul Akkerman.]]]
Your tank will be a lot cheaper than a plastic tank, have a lifetime of at least 25 years, and is easy to repair in case of cracks. The technology is extremely simple to implement, and semi-skilled construction workers can learn it with ease. Such tanks have been used on a wide scale in Asia and in some African countries, and there is huge scope for increased use for rainwater harvesting systems.