Seacrete is a mineral substrate grown directly from seawater through low-voltage electrolysis — a technology first proposed by Wolf Hilbertz in the 1970s and popularized by Marshall T. Savage in 'The Millennial Project.' A metal frame submerged in seawater and charged with a weak electrical current causes dissolved minerals (primarily calcium carbonate and magnesium hydroxide) to precipitate and accrete on the frame, building up a limestone-like material over weeks to months. The longer the current runs, the thicker and stronger the structure becomes. In 2200, seacrete construction has scaled from Savage's original vision of floating ocean colonies to the primary building material of Old Harbor's above-water structures and the Lake Michigan platform communities.