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Structural Terra
Cotta
By Bill Kibbel
Also known as hollow
structural tile, hollow tile block, hollow building tile, structural clay tile
and structural clay load-bearing wall tile.
Structural terra cotta is made from natural clay, or clay produced from
pulverized shale, that is extruded through a die (like Play-Doh®
spaghetti). Then, like brick, it's fired in a kiln to create a hard building
block. The hollow interior is divided into "cells" by a
"web", which gives it strength. The grooves, or ribbing, is on four
sides of the "shell" to help mortar, plaster and stucco adhere to the
surface. When used above grade, the interior has plaster directly applied and
the exterior is often coated with stucco. These are not vitrified or glazed. If
exposed to the weather, they can deteriorate. |
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It was most commonly used for buildings constructed
during the first quarter of the 20th century. Since stucco was usually the
exterior covering, Mission and Mediterranean revival styles are some of the
most common types of homes built with these blocks. It's also common in
military base buildings and gas stations built as late as 1940. It was also
used to back brick veneer.
Hollow tile blocks have also been used in commercial
buildings, even high-rise, but usually not for structural walls. Here the
blocks are often used as fill between steel structural elements and for fire
resistant wall construction, including interior partitions. They were installed
around steel beams for fire-proofing. They have also been used for fill in
concrete floors
Floor arches between steel beams could also be constructed
using "skew-back" terra cotta blocks:
These blocks are fragile as compared to other masonry
building units. This brittle quality makes them unsuitable for buildings in
areas where there is the potential for a seismic event. I've seen some damage
from mishandling or mistreatment after installation. Anchoring other building
materials can be tricky and the drilling often results in a
"blow-out" of an area of much larger diameter than the intended hole.
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The standard thicknesses
for exterior wall blocks was 6", 8" or 12". 12" was the
most common for 3 or 4 storeys. Over 4 storeys, I've always seen a steel
structural skeleton, with the blocks used as infill.
The dense, structural blocks have tremendous strength and are incredibly
light-weight as compared to any other masonry building material. The exterior
wall blocks typically have shell walls 1" thick and the webs are 3/4"
thick. The chart below shows some testing results, but these tests weren't
strictly on dense, load-bearing blocks. |
NEXT: Telephone Tile & Silo
Tile
Bill Kibbel, an expert in historic building
materials and methods, is a historic building
inspector & consultant.
©2004, Wm. Kibbel III
To contact our contributors you can
email us however, we cannot
answer specific questions or reply with any technical advice.
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