In this article, the author describes the work of Enrico Dini, who has developed a 3D printer able to print house-sized objects:

3D Printing A Whole Building

In Pisa, Italy, Enrico Dini has developed a machine called D-Shape which sprays a magnesium-based glue onto a thin layer of sand (at a resolution of about 25 dpi) to bind it into solid rock, which can be built up, layer over layer in a process that can include internal curves, ducting and partitions.

The following video is in Italian, but the images show you how the machine works. You have a big pile of sand and a spray arm that dispenses the glue that binds the sand together. After spraying a layer, more sand is added to the pile, it is leveled, and then sprayed again. You can jump forward 1 minute to see the machine and some of its output:

At the end of the process, the loose sand not bound by the glue is vacuumed away, leaving the structure behind.

The idea is conceptually similar to a smaller-scale rapid prototyping approach called Stereolithography, which is demonstrated in the following video. The laser is replaced by the spray arm, and the sand rises rather than having a platform fall into a vat:

Enrico Dini’s machine is the second technique that has been demonstrated to “print” a house. The first was developed several years ago by Dr. Behrokh Khoshnevis at USC and is demonstrated here:

[[[Jump to - A different way to build a house #41 – The ultra-secure house]]]