Page:Encyclopædia Britannica, Ninth Edition, v. 4.djvu/524

Rh 472 BUILDING [MASON-WORK. Quoins. Copings. Throafeinf &c., though both the former and latter are not unfrequently executed in plaster composition or cements. Quoin-stones are gauged and wrought blocks with parallel beds and vertical faces, placed on the angles of buildings in the Greek, Roman, and Italian styles, with the intention of adding to their beauty and strength, as in fig. 7, Plate XXI.; they are used in all kinds of walling, and are generally made to project before the face of that to which they are attached, mostly with a weathered angular joint, or with a rectangularly grooved or moulded one. The quoins are coursed with the rest of the wall if it be of stone, and are made to occupy the exact space of a limited number of courses of brick in a brick wall, or of flints where these are used. Copings in Italian work to cover walls, parapets, &c., are worked with a plain horizontal bed, two vertical faces, and an inclined or weathered back or upper surface, either forming an acute angle with the outer and wider, and an obtuse angle with the inner and narrower face, to throw the water off, shown at a fig. 9, Plate XXL; or slop ing to both sides from the middle, as at b ; the latter is technically termed saddle-back coping. In both cases they are made to project over the wall or parapet on both sides ; and in the projected part of the bed under the edge or edges towards which the inclination is given, a channel or groove, called a throat, is cut, to intercept the water in its inclination to run inwards to the wall. On gables or other inclined planes the coping is neither weathered nor throated, as the water is necessarily impelled along its course to the lower end, and not over the sides. It is a curious circum stance that the mediaeval designers rarely made their copings to project on the inside of a parapet, as shown in lig. 10, so that the exterior projection, which was returned up, was perhaps intended as much for effect as use. To protect the sepa rate stones of a coping course from the danger of being displaced by high winds or other accidental causes, and to form a chain through its whole length, the stones are linked together by cramps of copper or iron let into their backs and run with lead. These metals, however, especially the iron, for the most part act very inju- FIG. 1C. Copings. Cornices. riously, from their exceeding sensibility to atmospheric changes, and their greater or less tendency to oxidation ; indeed, the stone invariably suffers more than the work Joggles, &c. benefits from the metal cramps. Tenons, dowels, joggles, or dovetails, of stone, of hard word, or of slate set in Port- laud cement, applied so as to be protected from the weather, are far better, and would answer every desirable purpose sufficiently. Lead dowels, when small, are occasionally used. The value of joggling and doweling to stone-work is well exemplified in the construction of Eddystone light house. Cornices are but ramified copings, and are or may be subjected to the same general laws. Care must be taken, however, in arranging them, that their centre of gravity be not brought too far forward, in the anxiety to project them sufficiently, lest they act injuriously on the wall by pressing unequally, and their own seat be also endangered. String courses economically, in contradistinc tion to architecturally, are meant to protect a set-off in a wall, by projecting over its lower face in the manner of a coping, as in fig. 7, Plate XXL, at c ; the beds are worked parallel, and the outer face vertical or at right angles to them, but so much of the upper surface is weathered or sloped off as protrudes from the upper part of the wall to carry the water off ; and, for the reason above stated with regard to copings, the lower bed just within the outer face is throated. A stone string course, cramped or dovetailed in the bed, forms an excellent chain round a brick wall ; String course. Blocking course. but the part of it in the wall should be of the exact height of one, two, or more courses of brickwork. The woodcut, fig. 17, is a usual cornice or string course in the later period of mediaeval art in England. A blocking course is either a very thick string projecting over or flush with the face of the lower part of the wall to cover a set-off; or it is a range of stone over a crowning cornice to bring the centre of gravity more in on the wall than it otherwise would be ; in the former case it is treated exactly as a string, excepting that, if it be flush below, there is no occasion for a throat ; in the latter it has a horizontal case bed, parallel Fl vertical sides, and a weathered back or upper surface. Sills are weathered and throated like the parts of Sills. a string course, Plate XXL, fig. 7, a and b; yet in mediaeval work they may be seen flush with the upright of the wall. They are laid across window openings as a base to the sash-frame ; distinct sills in the same line may, indeed, be considered as an intercepted string course. In the ordinary practice of building, window sills are seldom set in brick walls until they are absolutely required to set the sash-frames on ; or they are set but not bedded, except at the ends. The object of this is to prevent any settlement that may occur in the piers from breaking the sills across on the unyielding part of the wall under the windows. A necessity for this, however, can only arise from bad con struction ; for with a good bond in the brickwork, all would settle together, and the sills might be completely bedded across at once. Landings are platforms of stone, either over an area Landing before a door, at the head of a flight of stairs, or as the floor of a balcony. They are made four, five, six, or eight inches in thickness, according to their extent and bearing if not one piece of stone they are of nicely jointed pieces joggled and plugged together, and are worked on the face and edges just as their situation may demand. They should also be very carefully pinned into the walls. Fig. 18 will show the danger, should they not be so, through the full length of their insertion. B If the front edge be pinned up, as at A, but a vacancy be left, as at B, the point C will become the fulcrum of a lever, and the landing have a tendency to turn at that point, and to break at the edge C. Every step and land ing should have 8 inches hold in a brick wall. All landings FIG. 18. Extremity of Land- should be well joggled ; the joint lllgt joggles made as at a, fig. 19, is called by workmen a he, and that at b a she joggle. An accident at the Poly technic Institution in London arose, no doubt, from the carelessness of the workmen, who put two landings toge FIG. 19. Joggles. ther, in which two she-joggles were worked, as in fig. 20, and filled the open space with plaster. There happened to be a large fossil in the stone close to the wall in the land ing 6, which, having no support from FIG. 20. Joggles badly joined. the other landing a, gave way, and caused the destruction of the lower portion of the staircase upon which it fell.