BUILDING. 641 BUILDING. platform cun-od to the exact arc of the intrndos of the arch. Work is then begun by laving' the bottom voussoir on each side of the arch. The sieceeding voussoir;- are then laid, one after an- no. 6. CEXTEE FOR COXSTHUCTIXG 8T0XE ARCS. other, working from both sides toward the top, and finally the top voussoir, or keystone, is in- serted. Between the voussoirs are mortar joints. Until the l<eystone is inserted, the .support of the centre is absolutely necessary to keep the arch from falling, and as a matter of fact it is usually left standing for some time after the keystone is in place, so that the mortar joints may harden before the strain of supporting itself is put upon the arch bv removing its cen- tre. Arches in building are constructed in a va- ' riety of styles, flat (Fig. 7i. elliptical, pointed, FIG. (. FLAT ARCH OF STONE. polycentrie, etc., but all styles are laid up ex- actly in the way described above. Piers in build- ing are column-like structures, used mostly as intermediate supports for interir)r columns or for girders. They are built of both rubble and cut stone, but more commonly of brick. In lay- ing stone piers, the mode of procedure is prac- tically the same as in laying walls. Trimmitigs in building usually denote all moldings, caps, sills, cornices, lintels, etc. Such pieces are usu- ally cut and dressed to form and dimensions ac- cording to the architect's drawing, and are fur- nished to the stonelaycr ready to set in place. In laying trimmings the stonelaycr has, there- fore, only to place them in their designated po- sition, with suitable mortar joints, and to bind them to the adjoining walls. Arch rings and trimmings are often ornamented by stone-cut- ting, and frequently this work is done after they arc set in place in the building. See Stone- ciTTi.xfi; Scri.PTiRE; Maso.nry; Cement; FoiND.Tioxs ; and Hiildino-Sto.ves. Bkicklatixc. is the process of laying up or joining together brickwork. Brickwork in build- ing includes piers, walls, arches, vaults, chim- neys, fireplaces, and various ornamental details and trimmings. Xo material except wood is so extensively used in building as brick. Bricks are made from clay and sand formed in molds and burned in kilns; they are produced in a great variety of shapes, sizes, colors, and styles suitable for the numerous purposes to which they ai'e put in building construction. (See Brick.) With the exception of arches, the process of bricklaying is practically the same for all kinds of brickwork used in building. It will be unnecessary, therefore, to consider separately walls, vaults, chimnejs, etc., as enumerated above. To build any kind of a brick structure so as to make it a strong and durable piece of work, it is necessary to have a bed of some kind of mortar between the bricks. Brickwork, therefore, consists both of mortar and bricks. The majority of brick buildings are built with common lime mortar, to which natural cement is sometimes added. For brickwork below grotind. hydraulic lime or cement mortar is used. In brickwork of common brick, the thick- ness of the mortar joints is from 3-lG of an inch to 3-8 of an inch, and every void in the work not occupied by other materials is filled with mortar. The usual way to specify the thickness of joint in brickwork of common brick is by the height of eight courses of the brick measured in the wall; this height should not exceed by more than 2 inches the height of eisht courses of the same brick laid dry. As common bricks are usually quite rough and uneven, it is not always easy to determine the thickness of a single joint; hence the larger unit of measure furnished by eight bricks is employed. Pressed bricks being smooth and true, enables the thickness of single joints to be specified. This is usually one-eighth inch. The methods of bricklaying for all kinds of brickwork except arches and trimmings can be illu.strated by describing wall-construction. A brick wall consists of two outside courses, joined together by one or more interior courses or fill- ing courses. The usual method of construction is to lay the outside courses first. The most ap- proved procedure in laying an outside coirse of bricks is as follows: The bricklayer first spreads mortar with a trowel along a bed for the brick, and also .scrapes a dab of mortar against the outer vertical angle of the last brick laid. He then presses the brick into its place with a sliding ntotion, which forces the mortar to fill the joints completely. Having continued the two outer courses of brick to an angle or opening, the next task is to fill the space between them or to lay the filling courses. This is done by filling the space with a thick bed of soft mortar and press- ing the bricks into this mortar with a downward diagonal motion, termed 'shoving,' so as to press the mortar u]) into the joints. By a repe- tition of the process described, the wall is con- structed, except that, if the face of the wall is to be plastered, the mortar projecting from the face-joints is scraped off llu.«h with the brick; or, if the wall is to be exposeil. the joints are 'struck' by holding the trowel obliquely and cut-
