Terra Cotta



The Pritchard Plumbing Supply building located at 433 Madison is a fine example of terra cotta masonry.
Photo from Memphis Heritage files.
 


Terra Cotta: Another ancient masonry type closely related to brick is terra cotta. Its principal ingredient is also clay. The primary difference between brick and terra cotta is that terra cotta is not a load-bearing structural material. It is used primarily for facing, or veneer, and is often ornamental, having been made in molds and then fired in the same fashion as ceramics. Terra cotta also shrinks during the process of firing. This shrinkage must be compensated for by enlargement of the original mold, allowing for the correct final proportions. Terra cotta is often glazed and pigmented. Like brick, if the glazing or outer skin is removed or damaged, the material will rapidly deteriorate. Architects and builders made use of unglazed terra cotta in their late Victorian residential and commercial building designs, such as the Rhodes-Jennings and Easy Way buildings on North Main Street. Glazed white terra cotta wall cladding was used in the Lincoln American Tower, Pritchard Plumbing Supply and the Advanced Rubber Stamp Company buildings, all early 20th-century commercial structures.

Clay Tile: Hollow clay tile became a popular material for lightweight construction of walls and vaulted ceilings during the late 19th century. 
It is, for the most part, not a load-bearing material and is utilized in panel construction, to fill space between structural members such as posts and beams in a skeletal frame system. Its initial rise in popularity stemmed from its being both fire-proof and light-weight. Clay tiles were used extensively in the construction of the old Ellis 
Auditorium walls.

Concrete:  Concrete had been used during the Civil War era as a 'grout' or 'gravel wall' construction. In this form, a slurry of cement, lime and gravel was poured into slip forms that were constructed of wood. However, the ready availability of wood and brick led to the abandonment of this practice. Concrete was later used for poured foundations by the early 20th  century and with the addition of iron reinforcing bars, such construction became quite strong and durable. By the 1920s, reinforced concrete construction was common, and was extensively used in commercial and industrial buildings. The old Federal Reserve Building on Jefferson, the Cotton Growers Association Building on Monroe and the old Armory (now the Children's Museum) on Central are all poured, reinforced concrete structures. 

Concrete was also produced in modular form as blocks of various sizes and textural finishes. The blocks were poured in forms, and after a short curing period were ready for use in construction. When they first appeared on the market, concrete blocks were considered 'technologically fashionable' and were left exposed. Patterns made possible by molds allowed some blocks to resemble hewn stone while others presented a vivid array of color from a variety of aggregates. However, exposed concrete block soon fell from fashion and became the infrastructure of the walls, hidden beneath veneers and the 'cladding,' i.e., the metal, wood siding or stucco. 'Rusticated' or 'split-faced' block has experienced a revival in the last decade for use in historically sensitive new construction. 

Related to concrete blocks is a process referred to as 'cast stone.'  In this process, a concrete mix, using a variety of aggregates and colorings, is poured into specialized forms for use as both structural and decorative elements. An example of the use of cast stone is Cravath Hall at Fisk University in Nashville. Many of the four-square houses found in midtown Memphis appear to be built with cast stone.   According to Dan Spector of Archicast, "The four-square houses of Midtown may have a thin mortaring of stucco, scribed to resemble big blocks, but since the color is plain grey and the concrete isn't cast, this cannot be considered 'cast stone.' We cast bright red stones to add to the Cossitt library's wall, and they are considered cast stone."

Mortar:  This discussion of masonry types would not be complete without a brief mention of mortar. The earliest mixture actually to be considered mortar was simply lime and sand, mixed with water to form a thick putty. Lime was obtained from burning limestone in kilns, then allowing the quick lime that resulted to slake by adding water to form a putty, then letting the putty cure for a specific period of time. This mixture formed a soft mortar that bonded with the masonry units in the wall, holding them in place while allowing them to expand and contract with changes in temperature and settlement. Being soft, however, this mortar was greatly susceptible to weathering and erosion. 

The solution to the problem was provided by adding a small proportion of Portland cement to the mix. However, the more durable a mortar becomes, the more rigid it is. If the mortar is actually harder than the main wall material, the result can be undue stress on the masonry units, retarding their natural movement and causing them to fracture and spall within the confinement of the unresponsive mortar. Concurrent with the growing use of Portland-type mortars, masonry types with similar characteristics (harder bricks) were developed to avoid this situation. Therefore, when re-pointing mortar (replacing mortar in joints that have eroded) on an old building, one must become familiar with the properties of both the masonry type and the mortar, and take appropriate measures to assure compatibility. The Secretary of the Interior's Standards for Rehabilitation are very strict about the composition of replacement mortar and a technical bulletin published by the National Park Service is very precise about actually having the original mortar analyzed for its composition so it can be replicated.