I just remembered another building material, which allthough not quite naturally produced, in the
end will be a mostly natural product: Seacrete (AKA Biorock)
An electrically conductive (but corrosion-resistant) structure(Iron for instance) is be submersed in seawater.
A buoy with solar panels and/or wind generators provides a small, but constant electric current.
A negative charge is run through a cable & through the submersed Iron structure while a positive charge
runs through another cable & through an electrode suspended in or near the negatively charged, iron structure.
In essence it's like growing a gigantic, thick clamm shell.
This image explains it better than words:
http://3.bp.blogspot.com...aHOONM/s1600/biorock.jpgWikipedia wrote: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) slowly forms around the cathode, eventually coating the electrode with a material as strong as concrete. Later experiments showed that the coatings can thicken at the rate of 5 cm per year. As long as current flows, the structure continues to get larger and stronger. It can also heal itself if damaged, making it particularly useful as a replacement for concrete in hard-to-access locations.
I highlighted some very interresting characteristics I found Seacrete to have. Allthough the growth process is relatively slow (about 5 cm per year), building large, solid structures like ships, submersibles, floating islands,
entire houses, walls, pillars and whatnot would become ALOT cheaper this way.
Also ALOT less labour intensive.
It would be a matter of submersing an iron mesh structure of the desired shape in the sea & anchoring it down.
Then release a buoy with Solar cells & anchor it to that same anchor. Then run down 2 cables from the Solar Cells
down below: The negative 1 to connect with the iron structure & the positive 1 to connect to an electrode.
Then you play the waiting game.
In 4 years the walls of your structure would be 20 cm thick. By then you could dive down to it & pump out all the water from the interior spaces & replace it with air from the surface.
(If valves are installed in all spaces' outer walls)
I guess you could also place large, airfilled bags inside of the interior spaces to keep the water out from the start, but you might have to use a significantly heavier anchor to counter the extra buoyancy. Then, after 4 years of growth, it's a simple matter of diving down and releasing the structure from it's anchor, and it shoots up to the surface.
If it's a house you could tow it to shore with a boat. If it's a ship then you'd just install engines,
electronics & mechanics into it and off you go. I bet you could grow floating islands like this.
And this island could continue to grow over time if current was continuously applied.