The precise composition of these plasters is kept secret, but it is generally understood that they are made from gypsum (plaster of Paris calcined at about 2250 of heat), to which some material or chemical is added to retard the natural quick setting of the plaster of Paris and make it slow enough setting that it can be mixed with sand and spread upon the wall. As well as the author has been able to discover the facts, the difference in these patented plasters is due principally to the chemical or other material used for the retarder.
The first of these plasters, and the first of all hard plasters placed on the market, was Adamant. This material was first introduced as a substitute for lime plaster at Syracuse, N. Y., in 1886. It is a chemical preparation, and the manufacture of the chemicals is covered by patents. The chemicals are manufactured exclusively at Syracuse, N. Y., by the original company and sold to licensed companies, who prepare and sell the plaster. There are twenty or more of these branch companies scattered throughout the country. The Adamant companies claim that the quality of their plaster is due principally to the chemicals used in its preparation. Adamant has been more extensively used up to this date (1896) than any other of the hard wall plasters.
The Windsor Cement dry mortar is made by mixing certain chemicals with Nova Scotia gypsum of a superior quality to form the cement, and the mortar is made by mixing with the cement washed and kiln-dried pit sand and asbestos fibre, all the materials being accurately weighed and uniformly mixed by special machinery. The mortar is made in the vicinity of New York City. It has been extensively used in many of the best buildings recently built in that city and to a considerable extent elsewhere.
A preparation, presumably of this class, called Granite Hard Wall Plaster, is made in Minneapolis, and similar preparations are made by local companies in several localities.
As far as the author has been able to ascertain all of these materials give good results when properly handled, although those which have been longest on the market are apt to be the most reliable.
All of the plasters above described are packed in sacks, or bags, holding either 100 pounds or a half barrel each.
Acme, Agatite and Royal are sold in the form of cement only, and the sand is mixed with the cement as it is used by the plasterer.
Two kinds of cement are sold, one mixed with fibre and known as fibred cement, and the other without fibre. The fibred cement should be used for the first coat on lathed work, whether of wood or metal. On brickwork, or fireproof tiling, fibre is not required, and the unfibred cement should be used.
The unfibred cement is also used for second or brown coat and wherever the plaster is to be troweled down to a smooth, hard surface. Where the plaster is to be finished with a white surface it is necessary to use lime and plaster of Paris (as on lime plaster) over these cements, as they are of a gray color.
Windsor Cement dry mortar and Adamant are sold mixed with fibre and sand, all ready for applying by simply mixing with clean water. Two grades of the Windsor mortar are made, one for lath work and the other for applying on iron, brick, terra cotta, etc., the only difference between the two being that the latter contains more sand than the former. Adamant is made in eight different grades for base coats on lath, brickwork or tile, for browning coat, and for finishing. Four different kinds of finishing material are made to give any style of finish desired.