3D printers have long been used in design labs, like the ones where tools are developed. The first time I saw one was in the late 90s at DeWalt’s prototyping lab. It created 3D objects by projecting a pair of laser beams into a vat of resin; the resin hardened where the beams converged. These days, the more common method is to use an extruder that moves on a 3D axis in response to commands that originate in a CAD program. They usually extrude layer upon layer of plastic or metal but the device developed by Andry Rudenko extrudes concrete—a custom blend of bagged concrete, sand, and additives. It cures rather slowly but is viscous enough to print with.
Rudenko, a Minnesota contractor with experience in engineering and architecture, built the machine in his garage and is the process of printing a small castle in his backyard (first video below). He eventually hopes to be able to print cheap full-size houses in 24 hours. In case you are thinking this is just one man’s crazy idea, think again because others are doing it. A Slovenian company called BetAbram is doing something similar (second video below) and a Chinese company called Winsun prints building components in a plant and transports them to the jobsite for assembly (third video below). They’re essentially doing panelized construction with concrete.