Page:Encyclopædia Britannica, Ninth Edition, v. 4.djvu/514

Rh 464 BUILDING BRICKWORK. pantile very useful for common purposes is the Bridgewater tile; it is rather wider than the common tile and has a double roll, being about 16| inches wide and 14 inches long. As plain tiling is heavier than slating, the plates and rafters of the roofs have to be made stouter than is neces sary for slates, consequently the expense of the roofing is added to, supposing that the same thickness of wall be suffi cient. The tile also imbibes one-seventh part of its weight or about 5 oz. of water in ten minutes, and takes many days to dry again thoroughly, this necessarily tending to deteriorate the timbers. Coping. When the top of a brick wall is not protected by a roof, it must be covered or coped in some manner, or it will soon be destroyed by the weather. Sometimes this is done by means of a course of bricks set across it on their edges in cement, and called a barge course, but it is a very imperfect covering, for water will trickle down the face of the wall on both sides, as the coping brick can be no longer than the thinnest wall is in thickness. Two double courses of plain tiles may be put side by side under the barge course, making a projection over each face of about 1^ inch, as shown in fig. 9. This is much better than the bai ge Section. Elevations. Brick cornices. Pointing. Barge course. Tile creasing. I3TITLL1LL8J1 course alone but still the covering receives no inclination outwards to throw the water off ; the upper surfaces are all horizontal. The same objection exists to foot-paving tiles, which are also used as a coping ; but none of these methods is available for any wall above 9 inches in thick ness. Stone coping, therefore, which may be made of sufficient width, and be both weathered and throated, is much to be preferred. One of the greatest faults in the modern practice of building, both architecturally as a matter of taste, and practically as a matter of prudence, is, that these copings, and cornices which serve as such, do not project sufficiently to protect the wall from the weather. A massive and well-projected cornice on a wall serves as a roof or pent-house to it ; and, besides imparting great beauty to the plainest structure, protects the wall from the premature decay of its upper part especially, and of the joints generally, if it be unplastered brickwork, which thereby calls for the frequent repetition of pointing. Effective and pleasing cornices and blocking-courses may be formed with uncut bricks alone; and these, set in cement, would, with judicious management, add materially both to the appearance and durability of brickwork, without the foreign aid of either the plasterer or the mason. Figs. 10 and 1 1 show two of the ap proved modes of form ing plain copings in brickwork to garden and other walls. From the injury which accrues to the joints Fi S- 10. Fi_ of brickwork through Brick Copings. bad management in its execution and imperfect protec tion when executed, arises the necessity, so frequent at tho present day, of pointing. Sometimes frost will have supervened before the surfaces of the joints in a wall are dry ; consequently, the mortar bursts and peels away, and the whole then requires to be pointed. Preparatory to this operation the scaffold, if it has been struck, must be re-erected, the mortar raked out of the joints to a depth of about of an inch, or deeper if the injury have reached further ; this can be done by a labourer ; a bricklayer then goes over the whole with a hard hair brush and water to cleanse and moisten the joints ; and then, with mortar prepared for the purpose, he carefully fills them all up, and neatly draws them with his trowel. This mortar must be of the best quality ; it is generally compounded with a certain proportion of forge or smith s ashes, which gives it a blue tinge, and adds greatly to its power of resisting the action of the weather. Cement is sometimes used instead of this blue mortar. If peculiar neatness be re quired, every joint is marked with a narrow parallel ridge of a fine white putty, in the composition of which bone-lime forms a principal ingredient. The former is called flat- joint, and the latter tuck-pointing. If it be an old wall that requires pointing, a scaffold must be erected before it ; and where the putlocks cannot be rested on window-sills and the like, half bricks are generally drawn from the wall to make rests for them, and restored again when the work is done. The former process is then gone through with a common wall ; but if it require tuck-pointing, the whole surface is well washed, and then coloured to look like new brickwork, before the pointing is done. The gauged arches over the windows and doors are always coloured, and the joints drawn with peculiar neatness. If in the original building of the wall the perpends have not been preserved, that is, if the vertical joints have not been made to fall perpendicularly in the alternately recurring courses, the workman in pointing stops up the old joints, which are irregular, with putty of a brick colour, and forms false new ones in the proper places. Arches in brickwork are plain, rough-cut, or gauged. Arches Plain arches are built of uncut bricks, and the bricks being Plain. parallelepipeds, an arch built of them must be made out with mortar; that is, the difference between the outer and inner periphery of the arch requiring the parts of which an arch is made up to be wedge-formed, as in fig. 12, Fig. 12. Fig. 13. which the brick is not, the difference must be made in mortar, as in fig. 13, so that the inner or lower angles of bricks used for this purpose should all but touch. The mortar should be more consistent than that used in ordinary walling ; and the centre on which an arch of this kind is set or built should not be struck or removed until the work is thoroughly hard, or rather all such arches should be set in cement which will harden immediately. In con sequence of this inherent defect in uncut-brick arches, in extensive continuous works, such as sewers, tunnels, vaults, tc., it is advisable to make them in thin independent rings of half-brick or one-brick thick, as the cass may be ; that is, a 9-inch arch should be in two half-brick arches, as at a, fig. 6, Plate XX., and an 18-inch arch in two one-bricks, as at b, each arch in the latter case being bonded in itself as in a common 9-inch v/.ill with headers and stretchers. It is evident that, by this mode of structure, a greater quantity of the solid material conies into the back or outer ring or arch than into the lower one ; and if they had been bonded together into one arch, as at c, all that difference must have been made up with mortar. Moreover, whatever pressure comes on the outer ring is carried by it directly to the inner or lower, from whose joints, however, the mortar cannot escape or be pressed out, the inner angles of the bricks, by meeting, preventing it below, and the bricks of the upper arch, which conveys the