Terrazzo

Contents

1. Venetian origins
2. From Fifth Avenue to the mid century floor
3. How a terrazzo floor is made
4. Care and restoration

Mike Kobeissi’s work, with guidance on staging, on design and on renovation, covers remodeling and buying as well as building and selling, and some of the floors it meets are older than they look. Picture a familiar moment in a postwar house. A new owner pries up a corner of tired wall to wall carpet in the entry, expecting plywood, and finds instead a cold, speckled surface: flecks of white, green and rust colored stone in a gray ground, cut into squares by thin lines of brass. A damp cloth brings up a dull sheen. The floor has been there the whole time, poured when the house was built and covered when tastes changed. It is terrazzo, and it has a longer history than the house.

Venetian origins

The material is an exercise in thrift. The National Terrazzo and Mosaic Association traces its modern form to the 1500s, when Venetian mosaic workers from the Friuli region found a way to reuse marble remnants, setting off size chips into terraces around their living quarters.⁵ Apartment Therapy describes those workers setting broken marble into clay and grinding the surface smooth with stones, and notes that the name is simply the Italian word for terrace.³ Leveling moved from hand rubbing to a long handled, weighted grinding stone called a galera, and the first sealer was reportedly goat milk, which brought out the color of the marble.⁵

Dates for the deeper past differ by source. The trade association places the earliest terrazzo like floors in what is now Turkey between 10,000 and 8,000 BCE and lists examples at Pompeii and Herculaneum.⁵ Elle Decor Italia dates the tradition to Greek and Roman times and its Venetian popularity to the 1400s, when waste stone from other work was bound with lime and later concrete.⁴ The craft had formal standing by 1583, when Venice’s Council of Ten granted the Friulian maestro Sgualdo Sabadin and his fellow workers in the art of terrazzo the right to organize.⁵

Figure

Terrazzo through the centuries

1. 01
   1500sVenetian mosaic workers from Friuli reuse marble remnants for terraces.
2. 02
   1583The Council of Ten recognizes the Friulian terrazzo workers.
3. 03
   1879Friulian craftsmen lay mosaic floors for the Vanderbilt residence in New York.
4. 04
   1924Divider strips and the electric grinder make the floor reliable and affordable.
5. 05
   1961The Space Needle is among the first projects in epoxy terrazzo.

From Fifth Avenue to the mid century floor

Friulian craftsmen brought the technique to the United States. The association credits the New York decorating firm of Herter Brothers with the first large scale marble mosaic floors in the country, laid by Friulian workers, and dates Christian Herter’s most elaborate commission, the William H. Vanderbilt residence on Fifth Avenue, to 1879.⁵ A national contractors’ association formed in Chicago in 1923.

Two inventions of the following year turned an artisan floor into a standard one. The International Masonry Institute explains that brass divider strips controlled cracking and the electric grinding machine made terrazzo cost effective.⁷ The association dates both to 1924 and adds that the strips let the floor expand and shrink while opening new room for pattern.⁵ By the mid century, as Dwell recounts, terrazzo was a familiar floor in airports, cultural institutions and hotels, valued for durability, low upkeep and the way it could be poured into shapes.¹ Epoxy binders arrived in the 1960s; the Seattle Space Needle, built for the 1962 World’s Fair, was among the first projects to use them.⁵ Later landmarks pushed the scale. Philip Johnson commissioned a terrazzo replica of a Texaco road map of New York State, 130 by 166 feet, for his pavilion at the 1964 World’s Fair; McCormick Place in Chicago received the first large epoxy floor in 1965; and Alexander Calder’s black and white terrazzo sidewalk went down in New York in 1970.⁵ The ubiquity had a cost to its image. Apartment Therapy recalls terrazzo as the drab floor of government buildings from the 1970s, a hard, stone like surface that later generations overlooked.³ In Italy, Elle Decor Italia observes, Venetian floors had by then become a cheap and popular option, remembered as the floor of a grandparents’ kitchen.⁴

How a terrazzo floor is made

At its simplest, terrazzo is chips of marble, quartz, granite, glass or other stone held in a cement or epoxy binder, then ground and polished.¹ This Old House distinguishes three types. Cement terrazzo, made with Portland cement over a concrete slab, is durable and labor intensive. Epoxy terrazzo is thinner, lighter and more flexible, accepts more colors and aggregates, and is common in commercial interiors, though it peels and fades outdoors. Precast terrazzo tiles are made off site and laid like ordinary tile, the least costly option and the least seamless.² The guide also sets terrazzo against other floors: it is less prone to etching and staining than polished marble and generally less slippery, and it lacks the grout lines of ceramic tile.²

Figure

Three kinds of terrazzo

	Cement terrazzo	Epoxy terrazzo
Binder	Portland cement	Epoxy resin
Build	Thicker, poured over a concrete slab	Thinner, lighter and more flexible
Color range	Traditional, more limited	Broader, with glass and metal aggregates
Outdoors	Used outside	Not suitable; peels and fades
Precast tile option	Least costly form, set like ordinary tile	Least costly form, set like ordinary tile

A poured floor follows a fixed sequence. The slab is cleaned, zinc dividers are cemented down in a grid of 3 foot squares, the mix of cement, chips and pigment is poured and pressed with heavy rollers, and after several days of curing the surface is ground with progressively finer diamond grit stones and polished.² The Masonry Institute adds the historical detail: installations were monolithic, bonded or sand cushion, toppings were standard, Venetian or Palladiana, and a typical topping ran a quarter inch to seven eighths of an inch thick, roughly 70 percent stone chips in 30 percent cement. A slurry of Portland cement filled pinholes before the final grind.⁷

Figure

Laying a poured terrazzo floor

1. 01
   SlabWash, sweep and scrub the concrete so the terrazzo bonds.
2. 02
   DividersCement zinc strips to the slab in a grid of 3 foot squares.
3. 03
   PourMix cement, chips and pigment, pour, then compress with heavy rollers and trowels.
4. 04
   CureLeave the floor to cure for several days.
5. 05
   GrindGrind with progressively finer diamond grit stones, then polish.

Care and restoration

Durability is the material’s main claim. This Old House says a well installed and maintained floor can last up to 100 years, and the trade association describes terrazzo as lasting the life of the building.²⁶ Routine care is plain: daily dust mopping, damp mopping with a pH neutral cleaner, and prompt cleanup of acidic spills. Resealing frequency follows traffic; a busy public space may reseal twice a year, a private house about every five years.²

Older floors call for closer diagnosis. The Masonry Institute advises that the causes of deterioration be fixed first, that cracks and spalls in the topping be repaired in place with small batches matched to the original chips and matrix, sometimes setting chips by hand, and that scratched cement terrazzo can be reground, grouted and polished. Severely damaged sections are usually replaced between divider strips, and abrasive or harsh chemical treatments are inappropriate.⁷ That preference for matched repair mirrors the Secretary of the Interior’s Standards and the guidance on clay tile roofs. Whether a floor found under carpet is worth restoring in a given house is best settled with a terrazzo specialist and the owner’s own advisors.

Figure

Inside a historic topping

stone chips

70%

cement matrix

30%

thickness of the topping

1/4 to 7/8 in

The revival has changed the look but not the method. Dwell notes bolder colors, larger aggregate and terrazzo furniture.¹ Elle Decor Italia describes Marmoreal, an engineered material of 95 percent marble and 5 percent polyester resin.⁴ A few terms make old specifications readable. Aggregate is the chip; matrix is the binder around it. A divider strip is the brass, zinc or copper line that controls cracking. The galera is the weighted Venetian grinding stone. Monolithic, bonded and sand cushion name ways of setting the floor on its slab, and standard, Venetian and Palladiana name the historic topping types. Precast pieces are made off site; poured in place work is laid where it will stay. Walls in the same houses carry a parallel vocabulary of scratch and brown coats, set out in the entry on lath and plaster.