Seacrete/Seament/Biorock

“The biorock building process (called accretion) grows cement-like engineering structures and marine ecosystems, often for mariculture of corals, oysters, clams, lobsters and fish in salt water. It works by passing a small electrical current through electrodes in the water. The structure grows more or less without limit as long as current flows.

Biorock technology arose from experiments in the 1970s when Hilbertz was studying how seashells and reefs grow, by passing electrical currents through salt water. In 1974, he found that as the salt water electrolyzes, calcium carbonate (aragonite) combines with magnesium, chloride and hydroxyl ions to slowly form around the cathode, eventually coating the electrode with a material similar in composition to complex magnesium oxychloride cements and as strong as concrete.

As of 2011, biorock coral reef projects exist in over 20 countries in the Caribbean, Indian Ocean, Pacific, and Southeast Asia.”
Wiki

Seacrete — Sea Water Electrolytic Mineral Accretion
“Seacrete samples range in strength from 3720 psi to 5350 psi. Typical concrete used in sidewalks and such is about 3500 psi. With very slow deposition -up to a year or more – strengths of 8000 psi have been achieved. One kilowatt hour of electric power will result in the accretion of 4.2 pounds of seacrete. Most of the research on Seacrete was published by Wolf H. Hilbertz. A thorough description of how seacrete buildings are grown is published by Marshall T. Savage. The Millennial Project (1994) p. 73 One of the most readable articles on secrete was published in Mother Earth News “Grow Your Own Buildings” (March/April 1980) p. 118”
Green Trust.org

Grow Buildings: Underwater Building Through Mineral Accretion
“Do you need a large container, a building, a boat, a breakwater, or even an entire island of your own? Well, if you happen to live near salt water, you just might be in luck, because you may soon be able to grow such structures! Not only that . . . but the “homegrown” constructions will be strong and durable, and—should they ever fracture—the same process that built them will enable them to heal themselves. Furthermore, the concept behind this breakthrough is so basic, so sensible, and so absurdly simple that you’ll wonder why no one ever thought of it before, and—more puzzling still—why so many people who have learned this method of growing buildings don’t rush out to try it.

Wolf Hilbertz (the inventor): “I saw that such creatures grow their shelters from the material closest at hand: the minerals suspended in the water all around them. ‘Why,’ I wondered, ‘can’t humans emulate coral?’ ”

Why not, the architect wondered, make a cathode of wire mesh material or hardware cloth? Why not shape such “fencing” like the finished building you want . . . and let electricity attract the minerals to the form?

Samples of the limestone-like substance were taken back to Austin, where tests revealed that the material was able to withstand pressures of more than 4,000 pounds per square inch, and was thus structurally stronger than the concrete normally used for driveway slabs and stairs. Yet the material was lighter in weight than is concrete, and—though the samples appeared porous—they didn’t weaken as they dried.

Here’s another interesting fact: So little electricity had to be trickled through the circuit—a maximum of 50 amps at 12 volts—that Wolf and two student assistants were able to swim through the electric field without feeling even a tingle. And the fish and other sea creatures—far from being repelled—seemed at times to actually be attracted to the field.

By 1975, when Professor Hilbertz published the first results of his experiments, he had discovered that both the growth rate and the strength of the material could be regulated by adjusting the spacing of the anodes and cathodes and varying the density of the current. He also found that large structures would be stronger if allowed to grow slowly . . . perhaps over as much as a year’s time.

Once the concept was shown to be valid, Wolf and his team began to think of structures that might be practical to grow underwater. Why not ships’ hulls? Why not beach houses that could simply be hoisted on shore once they were complete? Why not “forests” of components for land-based modular and prefabricated buildings?

Power for the first experiments was provided by the trickle charger, but Hilbertz was soon using small wind generators —set on a reef above the growing structures — that were capable of generating 60 to 200 watts in normal winds … more than enough electricity to produce even large buildings.

The simple wind generators cost $600 each, but our construction pioneer says that they could easily be duplicated by anyone handy with tools (using all new parts) for about $350 . . . and for a lot less cash if secondhand automobile alternators were used to generate the current.

At present, as a matter of routine, Wolf also grows large panels (about an inch thick, uniform in density, and considerably stronger than reinforced concrete of the same thickness) that are suitable for permanent, nonload-bearing walls. And he grows them in mere weeks . . . not months.

And here’s a side benefit to Professor Hilbertz’s building method: Early in his experiments the architect noted that—throughout the growth process—pure hydrogen gas bubbled up from the cathodes. Small-scale experiments suggest that it might be possible to collect the gas (which is a very versatile fuel), so that it could be tanked and piped ashore. (Since the sole by-product of burning hydrogen is pure water, many scientists see it as an important power source for the future.)”

Mother Earth News

How to Build a Ferrocement Boat
Image source: US Navy Ferrocement Boat Building Manual http://www.boatdesign.net/ferro-cement-boat-building-images/ferro-cement-boat-building-image-0024-1.gif
This boat building manual is free online. Here’s volume 1. http://www.boatdesign.net/ferro/ferro-1.pdf