Terrazzo—chips of marble, glass or other aggregates embedded in tinted cement, ground smooth and polished to a silky sheen—may have been yet another of mankind’s accidental discoveries. In the 15th century, mosaic artisans in northern Italy swept waste marble chips out onto their terraces, terrazzi, and smoothed the surface simply by walking over it. When workers learned to press the chips into a more permanent clay base, then grind and polish them with heavy stones, terrazzo caught on. Michelangelo used it in St. Peter’s Basilica. George Washington strode over it in his cherished Mount Vernon. In the 1950s, Richard Neutra and other modernist architects specified terrazzo in their designs, and by the ’60s, it covered floors in developer houses across the Southeast and Southwest. But as installation costs rose, terrazzo once again became a relatively pricey option—approx. $10 or more a square foot—for custom-built houses.
How to Install Terrazzo Flooring in 8 Steps
Step 1: Clean Thoroughly
A traditional terrazzo job like the one at the Ewells’ house consists of a cement and aggregate mix spread over a concrete slab to a depth of about half an inch. To prepare for the pour, workmen cut inch-deep grooves, called control joints, into the slab to guide the inevitable cracking as the concrete cures and shrinks.
Then comes a thorough cleaning as, from left to right, Jimmy Stewart, Walter Miller, James Crowder and Jason Aycock power-wash and sweep the slab to get rid of loose debris. The cleaning is followed by a scrubdown with dilute muriatic acid to kill algae, which can weaken the bond between the concrete and the terrazzo.
Step 2: Cement Dividers to Slab
Next, zinc dividers are cemented to the slab, creating a grid of 3-foot squares. To stop wet terrazzo from flowing into the parts of the slab where walls will be built, plywood strips are temporarily fastened to the perimeter. Right before the pour, the entire surface gets a thin coat of an epoxy solution. With the slab prepared, the terrazzo ingredients are combined according to a precise recipe: in this case, a quarter-pound of black pigment for every 94-pound bag of white portland cement and 200 pounds of marble chips. The chips are a mix of three colors: Cardiff green (70 percent), raven black (25 percent) and Georgia white (5 percent).
Steps 3: Pour It Out
“Pour it out!” hollers foreman Alan Aycock as Keith Kelly and others fill wheelbarrows with the dark-gray mud, push them up onto the slab and dump the loads. The terrazzo is immediately spread and compressed with a heavy roller.
Step 4: Work It Down
To work it down even more, some of the men get out their floats, bend low and trowel the surface.
Step 5: Scatter the Mix
Like a farmer feeding his chickens, a worker scatters even more of the aggregate mix to make sure the finished surface will be packed. When foreman Aycock yells, “Roll it off!” the heavy roller returns to further compress the aggregate and force out air bubbles. The cement is allowed to cure for two days. When the terrazzo kings—as the workers call themselves—return, the mud is still dull and lumpy but hard as granite. At Aycock’s next command, one of the kings guides a 500-pound grinder across the floor.
Step 6: Smooth Out Lumps With Spinning Stones
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.
Step 7: Shovel the Dirt
Carlos Ines keeps the cement from spilling off the slab by shoveling a dirt dam onto the perimeter.
Step 8: Grind the Surface
When the cement sets, Benny Byrd makes a few passes with a smaller grinder to polish out any remaining scratches. By this time, the men can look down at the gleaming surface and see reflections of themselves at work.
It’s the aggregate, the colorful chips, that distinguishes terrazzo from plain old cement and lends it an artful complexity. Shiny glass, iridescent mother-of-pearl and bright plastic—in addition to traditional marble—offer a range of colors and virtually unlimited combinations of chips and pigments. To control the look of the finished product, terrazzo installers start with standard mixes, established by the National Terrazzo and Mosaic Association, and then make samples for their clients. “People want to coordinate with other flooring such as carpet or tile or even stone,” says Dave Roberson of the David Allen Company, the Ewells’ installer. “We can pretty well match a granite to where you can hardly tell the difference.” After finalizing the recipe, Roberson goes to great pains to maintain consistency in the field, weighing and packaging the pigment and mixing the aggregates at the shop. “Even then,” he says, “everything affects the color: humidity, temperature, even the amount of water. It’s really more of an art than a science.”
Terrazzo Flooring at Film Center
Starting at the end of the last century, terrazzo craftsmen found a lot of work in hotels, schools and office buildings. Tough and economical, the material inspired creative designs, thanks to its free-flowing nature and to the zinc and brass divider strips that could define any shape or pattern. Next time you amble through a lobby, a train station or the halls of academia, check out what’s underfoot. As the examples shown below demonstrate, some amazing floors have surfaced from a pile of chips and cement.
Film Center, 630 Ninth Avenue: Completed in 1929 and named a New York City Landmark in 1982, the ornate art deco building still delights visitors with its original lobby floor, a geometric mix of terrazzo and solid marble.
Terrazzo Flooring at Time & Life Building
Time & Life, 1270 Avenue of the Americas: Built in 1959, the 47-story limestone-and metal-clad tower in New York City’s Rockefeller Center not only has a wavy terrazzo lobby but also an outdoor promenade paved with the same design.