Spinning a dozen 4-inch-diameter diamond-grit stones, the machine slowly smooths the lumps. A smaller, more maneuverable grinder the size and shape of an elephant's foot works into the corners and around plumbing, electrical and other projections. After several passes, the stones are replaced with those of finer grit to sharpen the shine. It takes most of a day to polish the floor and bring to light the silvery zinc-bordered squares and the sparkling marble colors. Hosing down the terrazzo reveals tiny pinholes, evidence of bubbles the roller didn't squeeze out. To fill them, a thin slurry of tinted cement is spread across the entire floor.