Hidden Treasures: Exposed Aggregate Concrete in the Early 20th Century
You might think of exposed aggregate concrete as a modern utility material used to add some visual interest to sidewalks, driveways, patios, pool decks, and outdoor plazas. A recent trip to the town of Wishaw – just outside of Glasgow, Scotland – peaked my interest in the material because of its use on a great number of new residences throughout the town. But it turns out that exposed aggregate concrete has been used as a building material – albeit somewhat less commonly – for over a century.
Most people trace the origins of exposed aggregate concrete back to John J. Earley, who patented his “Method of Producing a Predetermined Color Effect in Concrete and Stucco” with the United States government in 1921. Although this may have led to large-scale production and widespread use of exposed aggregate concrete panels, such structures have been made locally since the beginning of the 20th century.
By the turn of the 20th century concrete had been accepted as a viable architectural material and its aesthetic qualities were being explored. Pre-cast concrete often mimicked natural stone; however, many in the concrete business were aware of the aesthetic effects of exposed aggregate concrete. Two well-known examples of early exposed aggregate concrete are Ernest L. Ransome’s work at Stanford University and Frank Lloyd Wright’s Unity Temple in Oak Park, Illinois.
Because of the specific skill set needed to create the proper unity of texture, the process of making exposed aggregate concrete remained in the hands of the craftsman in the early 20th century. To create this aesthetic, the first step was to select the proper coarse aggregate to give the desired color and texture. Whether cast or poured concrete, after a day or two the forms would be removed and the surface abraded or tooled to expose the aggregate. Once the aggregate was agreeably exposed, the surface would be treated with dilute acid to intensify the color.
This was a popular material for railroad and highway structures, and it became the material of choice for many bridges and other public transit structures of the 1910s and 20s. Although this was happening across the country in places like Chicago, Philadelphia, and Cleveland, let’s highlight some structures in the New York City area.
With the development of the state highway system in New Jersey in the 1920s, many bridges were made of exposed aggregate concrete. Remnants can still be seen along New Jersey State Highway Routes 1 thru 20. The bridges are often engraved with the date of construction and the state highway route number.
There are a couple of existing exposed aggregate concrete railroad structures along the Morris & Essex Line of the New Jersey Transit that were constructed as part of a campaign of improvements in the 1910s: the Madison station (c. 1915-16) and the Far Hills station (c. 1914). A unique example of early exposed aggregate along the Babylon Branch of the Long Island Railroad is the station at Forest Hills, constructed in 1911. This elaborate example of early 20th century exposed aggregate concrete relates to the larger residential complex, Forest Hills Gardens.
Although exposed aggregate concrete appears to have been used in many early 20th century railroad and highway structures, it took a more rare form in private buildings – few of which can be found in the New York City area. Forest Hills Gardens is one particularly interesting residential example of exposed aggregate concrete c. 1905 in Forest Hills, Queens. This community development was the brainchild of Grosvenor Atterbury, a New York architect, and was praised as “a scene for picturesqueness not equaled anywhere in America and for an artistic use of concrete unequaled in the world.” Many of the residences are composed of large pre-cast concrete block that has been treated to expose the gravel aggregate and crushed red tile, which also covers the roofs. Forest Hills Gardens truly represents a unique example of early 20th century exposed aggregate, as well as a step toward the commercialization of the process patented over a decade later by John J. Earley.
It is rare to find exposed aggregate concrete structures constructed before the 1930s and 40s, when the Earley process was put into production. Only a few have been highlighted here, most in the New York City area. Do you know of any of these unique structures in your area?
- Heather Hartshorn, PresArch