I have blogged about how 3D printing could change the game for the saltwater aquarium hobby with my series on using 3D printers to design and develop products at home inexpensively for use with aquariums. 3D printers like the Makerbot and Reprap extrude a hot noodle of plastic and build a part layer-by-layer. This project diverges from that aspect and instead sprays a soil / binder mixture three dimensionally using a robot to build a shape. The project is called Stone Spray.
The Stone Spray project is a new technology developed by architects Petr Novikov, Inder Shergill and Anna Kulik in conjunction with the Institute for Advanced Architecture of Catalonia, supervised by Marta Male-Alemany, Jordi Portell and Miquel Lloveras.
As mentioned, a robot sprays a soil / binder mix into a three-dimensional shape and then dries in place. The technology is reportedly ecologically friendly using very little energy to function and can run off of solar power. The group also has an ebook explaining the project in more detail.
Take a look at some of the shapes that the project has created: