Structural clay tile describes a category of burned-clay building materials used to construct roofing, walls, and flooring for structural and non-structural purposes, especially in fireproofing applications. Also called building tile, structural terra cotta, hollow tile, saltillo tile, and clay block, the material is an extruded clay shape with substantial depth that allows it to be laid in the same manner as other clay or concrete masonry. In North America, it was mainly used during the late 19th and early 20th centuries, reaching peak popularity at the turn of the century and declining around the 1950s. Structural clay tile grew in popularity in the end of the nineteenth-century because it could be constructed faster, was lighter, and required simpler flat falsework than earlier brick vaulting construction. Each unit is generally made of clay or terra-cotta with hollow cavities, or cells, inside it. The colors of terracotta transform from gray (raw, moist clay) to orange, red, yellow, and cream tones. This is due to an effect of the firing process which hardens the clay so it can be used for structural purposes. The material is commonly used in floor arches, fireproofing, partition walls, and furring. It continues to be used in Europe to build fire-resistant walls and partitions. In North America the material has largely been replaced by concrete masonry units.
History, Origins, and Development
Pre 1850s-1870s Clay tiles have been used in various ways for thousands of years. The Romans were among the first to use clay tile in construction by building clay pots to lighten vaulting loads. However the first recorded structural use of terra-cotta forms was in sixth-century Italy in the dome of the Church of San Vitale in Ravenna. Clay pots lined with plaster of paris lightened the load of the dome in a similar way to earlier Roman construction.
1850s-1870s
The first recorded use of structural clay tile in the United States was in 1853. Frederick A. Peterson designed hand-shaped clay ovals that he placed between I-beams and covered with cement to create flooring. Peterson debuted his method in the Cooper Union Building in New York City. However, Peterson's method was not mass-produced or replicated until the 1870s. In 1871, Balthasar Kreischer and George H. Johnson patented a new method similar to Peterson's, based on earlier precedents including those of British architect Joseph Bunnett in 1858, as well as designs by Peterson. Each of these methods emerged out of a growing need to fireproof buildings following massive fires across the United States during that last quarter of the nineteenth century. Before the widespread use structural clay tile, brick and masonry construction dominated fireproofing techniques. However, brick and masonry construction, especially vaulting, was heavy, time-consuming to construct, and required the construction of costly custom formwork. Structural clay tile offered a lighter, faster, and simpler alternative. In the early 1870s, an interlocking system of angular clay tiles, designed to fit together with a keystone, gained popularity following the mass production of Vincent Garcin's designs for flat segmented arches. This flat segmented arch, developed by Garcin, was first used in the United States at the New York Post Office, Kendall Building in Chicago, and the Singer Manufacturing Building in St. Louis, becoming the most prolific use of hollow clay tile until the end of the century.
1880s-1900s With its increased popularity, structural clay tile became one of the most popular materials for fireproofing iron and steel construction. However, its capacity for fireproofing was not fully realized until Peter Bonnett Wight invented the "tile shoe" in 1881. The "tile shoe" covered the exposed side of metal beams, fully insulating them from fire.
1910s-1950s Flat arch construction grew in popularity with the increasing number of buildings using steel and iron structural members in their design. New building code requirements for fireproofing aided in the use and proliferation of structural clay tile in skyscrapers and other large buildings. After 1910, manufacturers began to test and develop stronger and more complex structural clay tile systems that worked better in compression. Greater compressive strength, found largely in the invention of the end pressure arch, allowed the material to be used in longer floor spans. However, as reinforced concrete grew in popularity as a cheaper and less complex alternative, structural clay tile use in floors and roofing declined. Increasingly, clay tile was used inside concrete flooring to make it lighter, or as centering/formwork for concrete construction. With the rise of reinforced concrete flooring and metal decking, structural clay tile fell out of popularity for use in horizontal applications. While the use of structural clay tile in flooring and roofing declined, its use in walls enjoyed popularity into the 1950s. Wall tile blocks continue to be manufactured, but specialty tile units often require custom commissions. Clay tile arches are no longer manufactured and due to a lack of skilled artisans to lay the arch systems, they are never replaced.
Horizontal Application
Tile Floor Arch Types
Side Pressure Arch Construction Side pressure arch construction, the first method used in tile floor arches, is composed of hollow tiles laid parallel to I beams.
End Pressure Arch Construction End pressure arch construction is composed of hollow tiles laid perpendicular to I beams. This method enjoyed popularity after it was discovered to be fifty percent more efficient than side pressure arches.
Book Tile A popular use of structural clay tile was book tile, a flat hollow tile, that was used in roofing systems. Book tile was also used in raised flooring to allow plumbing and other systems to be run in buildings.
Composite Construction In the late 1890s, the most popular system of tile floor arches combined both side and end pressure construction. With the increase in popularity of concrete construction, composite construction began to use both methods in conjunction with reinforced concrete. Later systems used clay tiles and reinforced concrete to replace tile floor arches in the 1930s.
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