CONSTRUCTION IN STONE.
Structures in stone appear either in massive form as masonry or more specifically as stone along with framework and the shell-like form known as face-work. The choice of the bnilding material, which may be either natural or artificial stone, will depend on the nature of the service for which it is designed. Natural stone which can be worked into regular shapes—as, for example, granite, sandstone, and marble—is designated as " cut stone," while that used in irregular shapes is called " broken." Arafura/ Sione of all kinds, being rough in the natural shape, must for every portion of a building except foundations be shaped into forms suitable for its position. In so doing there should be considera tions as to economy of mortar and cement and provision for ornamental designs. Stronger walls may be built of stone than of brick (thongli those composed of the latter will stand far more heat in a conflagration), and such stone is either rough or hammered, with edges dressed true from !.f. inch to -EY? inches around the four joints of the front, or plain and very perfectly fitting pieces are chiselled smooth or highly polished, as in gran ite, both forms being often intermingled in the fronts of buildings. Stone, usnally granite or sandstone, either rough or smooth and polished, is now extensively employed for the largest and best buildings in the chief cities of the United States. The rough is not confined to any particnlar portion of the front or sides, but is used much for arched work, and chiefly in the basement or first story.
Rubble Stone for walls is very common in the United States and Europe; in the former conntry some small towns are built almost entirely a it, where the stone can be conveniently obtained.
A typical instance is the older portion of the suburb of Philadelphia known as Germantown. Irregular stones, large and small, such as are used for foundations and cellars, are built in walls of from two to four stories' height, with sufficient cheap mortar similar to that made with gravel and lime, care being taken to fill all interstices with small fragments of stone. The outside can be finished in stucco or by pointing the joints
with better mortar. To prevent dampness, the walls inside are often stripped with wood before plastering. Alany very costly rural dwellings, barns, and even public halls and school-houses, in the United States are constructed of irregular pieces of the best kinds of stone, in the same man ner as above stated, the best mortar being used. The inside half or two-thirds of the walls of such buildings are frequently composed of ordinary rubble stone and the more common descriptions of mortar.
Artificial Stone IUal ls. —Air-dried bricks (for adobe structures) are formed chiefly' of clay; if hardened by fire, they are called burned bricks. Buildings of materials known variously as concrete, beton, Pise, etc., must be included under the head of constructions in stone, as the mass, though at first soft, so that it can be moulded to take any desired shape, soon hard ens and becomes in all respects similar to stone. Concrete and beton walls are composed of small pieces of stone mixed with gravel, sand, and cement; of the last there are many kinds, of which the celebrated " Portland " is a prominent type. The plastic material is rammed tightly into strong wooden moulds, which are allowed to remain until the work has set, and are then moved upward. This description of walls has been adopted to a considerable extent in England and France for medium and small houses, but has as yet been but little used in the United States.
Concrete 'al Is. —In concrete walls, whose structure is shown in Figure ro a the applied material is hydraulic mortar mixed with fragments of stone, rubble, etc.; sometimes a mixture of lime and sand only is used. The picture is taken from I,acroix's Eina'es stir l' EA75osit ion (Paris, 1867), and exhibits the manner of constructing workingmen's houses of such con crete walls. As will be noticed, pillar-shaped moulds are first erected at the corners and central parts, between which, as the work progresses, the horizontal moulds are gradually moved upward in the same manner as above stated.