His work appears in numerous prominent projects designed by major architectural firms in New York and other cities of the Northeast.

Guastavino tile is found in some of New York's most prominent Beaux-Arts landmarks and in major buildings across the United States.

In 1881 Guastavino came to New York City from Valencia,[2] with his youngest son, nine-year-old Rafael Jr.[3] In Spain he had been an accomplished architect and was a contemporary of Antoni Gaudí.

Guastavino was commissioned by the firm of McKim, Mead, and White for their Boston Public Library (1889), which increased his reputation with every major architect on the East Coast.

[2] His published drawings of interior decoration of the Spanish Renaissance style caught the eye of an architect, who asked him to submit a design for the planned New York Progress Club building.

[3] The property holds artifacts that may be visited, including the kiln and chimney, a wine cellar, beautiful old stone walls, and many smaller structures that have been rediscovered as modern buildings have been constructed there.

In Boston, Guastavino tiles are found in the Boston Public Library; in New York City, in the Grand Central Terminal, Grant's Tomb, Carnegie Hall, the American Museum of Natural History, Congregation Emanu-El of New York, and St. Bartolomew's Episcopal Church; and in Washington, D.C. in the U.S. Supreme Court building and the National Museum of Natural History on the National Mall.

Guastavino tiles form the domes of Philadelphia's St. Francis de Sales Roman Catholic Church.

[6] The largest dome created by the Guastavino Company was over the central crossing for the Cathedral of St. John the Divine in Manhattan: it is 100 ft (30 m) in diameter and 160 feet (49 m) high.

[8] His son Rafael's Mediterranean villa (1912), built entirely of Guastavino tiles, still stands on Awixa Avenue, in Bay Shore, Long Island[9] and was added to the National Register of Historic Places in 2013.

They had three sons together, but Guastavino had an affair with nanny Paulina Roig, after which Pilar left her husband, later moving to Argentina.

It is believed Paulina was the mother of Guastavino's fourth son Rafael Jr., and the three, along with the two previous daughters she had, moved to New York City together in 1881.