This section is from the book "A Treatise On Architecture And Building Construction Vol2: Masonry. Carpentry. Joinery", by The Colliery Engineer Co. Also available from Amazon: A Treatise On Architecture And Building Construction.
137. The uses of terra cotta in architectural work are so varied and extensive as to be almost endless. Both for inside and outside decorative and plain work, it forms a very important substitute for stone and brick, especially in positions exposed to the weather.
Although terra cotta has come into extensive use within a comparatively recent period, it has met all requirements very satisfactorily, showing itself to be of the utmost value as a durable building material. In Europe are to be seen many examples of terra cotta which have endured the changes of the weather for hundreds of years and yet remain in good condition, while stone similarly exposed has become more or less disintegrated.
The great value of terra cotta for building purposes consists in its durability. If made of the right kind of materials, and properly burned, it is practically impervious to moisture, and hence is not injured by frost, which is such a powerful destructive agent in many building stones. Atmospheric gases, likewise, have no effect on well burned terra cotta, and dirt gathering on it is washed away by rain. Another point of value is that it affords no lodgment for vegetable growths, as do some stones. When terra cotta is not sufficiently burned, it lacks the proper surface vitrification, and is then to some extent absorbent, and, consequently, not so durable. The heat-resisting power of terra cotta also gives it a great advantage over other materials, and makes it very desirable to use for trimmings and ornamental work in fireproof buildings.
Economical Advantages. The cost of terra cotta varies according to the size and amount of work required. Plain sills and caps can be obtained at about the same price as those of dressed sandstone, when the price of the rough stone does not exceed 90 cents per cubic foot. When many pieces of the same size and shape are required, terra cotta can be had much cheaper than stone, unless the charges for transportation are very high. When there are many molded and decorative features which would necessitate much hand work for dressing and carving, if stone were used, the advantage in terra cotta in point of cost is evident. Further economy may be obtained by repeating the detail of the ornamental features, so as to require the fewest possible different pieces. Very often suitable designs may be found in catalogues of terra-cotta manufacturers, by using which the cost will be considerably less than when new patterns and molds must be made for the work. Another advantage is that terra cotta weighs less than stone, and, consequently, lighter walls may be made, when the former is extensively used, than if the work were wholly of stone.