344. By using only the best materials and mixing them in the manner described it is possible to obtain a very good quality of wall plaster, but there are so many chances of getting an inferior job when ordinary lime plaster is used, that a material which can be used with greater certainty is very much to be desired. Such a material appears to be found in the improved wall plasters recently placed on the market.

There are now several improved plasters manufactured by different companies which, although differing in their composition, apparently give about the same kind of wall.

The general name given to these improved or patented wall plasters is that of "hard wall plaster" or mortar.

There are two distinct classes of hard plasters, which may be designated as natural cement plasters and chemical or patented plasters.

Natural Cement Plasters. - In this class are the Acme, Agatite, Aluminite, Climax and Royal, the first and last names being perhaps the best known.

The earth from which these plasters are produced is found in various portions of Kansas and Texas. It is of a light ash-gray color and of about the consistency of hard plastic clay, which it much resembles in appearance, although its chemical nature is more like that of gypsum.

When calcined it assumes a pulverized form. When mixed with water it sets like hydraulic lime or cement, but much more slowly, so that ample time is afforded for applying the mortar.

A sample of agatite, after several weeks setting, broke under a tensile strength of 370 pounds per square inch. It is superior in strength to most of the hydraulic limes and natural cements.*

The various deposits from which the plasters above mentioned are produced appear to be of about the same grade of earth, the plasters differing, if at all, only in their strength and working qualities, which is due principally to slight differences in the process of manufacture.

The Acme cement plaster is produced by calcining the natural earth at a high degree of heat (about 600° Fahr.), which rids the material of not only the free moisture, but also the combined moisture.

The resulting plaster is slow setting, works smooth under the trowel, and does not come to its normal strength until thirty or sixty days after it is spread.

These cement plasters are remarkable for their great adhesive quality. They will stick firmly to stone, brick or wood without the aid of hair or fibre. Acme cement has been used to some extent in New York for setting fireproof tiling, and has been found superior for this purpose to the ordinary natural cements.

Acme cement plaster was the first of this class to be put on the market. It has been extensively used throughout the country, and makes a very superior wall plaster. Large quantities of it were used in plastering the World's Fair buildings, Chicago. Agatite and Royal, although more recently introduced, have also been quite extensively used, particularly on large and important buildings in the West. Climax is produced especially for the Southern trade.

* Professor Edwin Walters, in Kansas City Journal, January 20, 1893.