At first it doesn’t look like much. Just a concrete wall, 3 feet high and 5 feet long, sitting on the floor of a laboratory in Los Angeles. But this wall wasn’t poured. It was “printed” by the machine next to it, a robot armed with a concrete pump and a pair of trowels. Although the wall is nicely crafted, with a uniform surface and smoothly rounded ends, it’s just a trifle when compared with the robot’s next job: building a 2000-square-foot house.