Feb 16 (Reuters) - Most homes are built block by block, or brick by brick.
But a demo house in Calverton, New York, was constructed scan by scan - its walls made using a giant three-dimensional printer.

The demo house was built by construction firm SQ4D, to show the public and industry what was possible. Now the company is putting one up for sale - a still to-be-built house in the nearby town of Riverhead, which has been listed on property site Zillow at $299,000.

With a detached garage, the house will cover some 1,400 square feet (130 square meters).

The footings, foundation and slab, along with the walls, will be entirely made with the 3D printer.

"We instruct the machine to go around and follow your floor plan each pass as we go by. We're constantly building up," said Kirk Andersen, the director of operations for SQ4D.

Andersen and his colleagues had to design and build their own printer to fulfill their house-sized dream.

"We took the idea of a plastic 3D desktop printer and wanted to make it much larger and spit out concrete," said Andersen.

"We set tracks on each side of the structure where we plan to print. We set up our giant gantry, our large scale printer goes back and forth, extruding these layers one by one, stacking, building all your walls."

Andersen said the actual printing time for the walls took about 48 hours, part of an overall eight-day process to build the entire home.

That is significantly faster and around 30% cheaper overall than a home built using standard construction methods, he said, where laborers need to tow in and stack blocks manually.

"We show up with a printer. We can replace the labor-intensiveness of those guys and extrude concrete much faster than they can lay the bricks," he said.

Not everyone in the construction industry is thrilled at that prospect, and the process has received mixed feedback, he said, with some skepticism in particular from older tradesmen.

"I think people are just unprepared for how this is going to change construction," said Andersen. "This is the beginning. This is just scratching the surface right here."

(Reporting by Reuters TV, Writing by Rosalba O'Brien Editing by Marguerita Choy)