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Telephone Tile &
By Bill Kibbel
For as long as I can remember, I've run into folks
incorrectly referring to structural terra cotta
as "telephone tile" and occasionally "telegraph tile".
Telephone/telegraph tile was specifically manufactured for containing and
protecting underground communication cables. It is quite similar to the
hollow tile blocks used in building
||The interior of multi-duct terra cotta
conduit is also divided into "cells" by a "web". The cells
however were the ducts for the cable installations. Unlike the building blocks,
the exterior shell is smooth, not ribbed for plaster and stucco applications.
The corners are usually rounded and some have a bell joint at each end for
joining to other blocks. Others have fine grooves at each, so that mortar
applied to the joints will bond, to seal the joints between each unit. The
shell is also usually vitrified, unlike the unglazed blocks manufactured for
Although telephone tile is mistaken for an actual building material, and not
manufactured or tested for use in building construction, it has more than
occasionally been adapted successfully.
|Silo Tile is also a hollow
structural terra cotta product used for constructing round towers. The
individual blocks are quite thin as compared to the other building tiles -
usually 6 inches or less. The are also slightly curved.
They were a significant improvement over the wood stave silos, but there were
concerns that silage wouldn't keep as well. This appears to be unfounded as
stone silos had been in use since at least the 18th century.
|| The hollow tiles used for silos were vitrified or
glazed. This reduces the absorbtion of water, eliminating the need for a cement
coating. Salt glaze was used for a period, which made the tiles even more
impervious, but it resulted in a weaker structure.
There are many, many surviving tile silos that are quite well preserved and
more pleasing to look at than steel or concrete silos. They are at least 75 to
80 years old as the mid 1930s was about the time that concrete silos had
completely taken over.
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Bill Kibbel, an expert in historic building
materials and methods, is a
inspector and consultant in southeastern PA
& central NJ.
©2004, Wm. Kibbel III
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