|Rudeno's 3d printed house/castle Photo courtesy Andrey Rudenko|
A bit more details now. The guy's name is Andrey Rudenko and he is from Minnesota. More or less what he has done is create big 3D printer and use something like concrete for printing material. However this was not so simple, first he had to scale the existing designs for 3d printers and solve a lot of problems, which are non-issue for the smaller printers, but serious obstacles for a big one and as far as I can see he essentially designed and build something completely new. Second he had to create the printing material based on cement with a lot of trails and errors so he could finally achieve the strength, viscosity, speed of hardening, etc. After that he had to (re)make the software for the printer. And there were a lot more issues, that as an hobbyist myself I am sure he had but never mentioned in the articles.
And finally for these that would like to make a more in dept research I've put a link to his web site.