Wiktionary
n. a plaster compound creating the trompe l'oeil appearance of rock.
Wikipedia
Formstone is a type of stucco commonly applied to brick rowhouses in many East Coast urban areas in the United States, although it is most strongly associated with Baltimore. Formstone is commonly colored and shaped on the building to imitate various forms of masonry compound, creating the trompe l'oeil appearance of rock.
Formstone was patented by Albert Knight of Baltimore in 1937, although a similar product named Permastone had been invented in Columbus, Ohio, eight years prior. The name Formstone was actually a brand name used by Knight. Permastone, Fieldstone, Dixie Stone, and Stone of Ages were names used for a product similar to Knight's Formstone, particularly in other cities.
Usage examples of "formstone".
Idly, he reached into a secondary control space, flicked on the controls that would allow the Imani Formstone Works to produce copies of his originals.
One of those was the Valencia Motel, a tired, eighty-unit structure of brick, Formstone, and tan siding.