Fig 68. Chimney. Whole-Brick external walls. English Bond.
It will be seen that the cross withes are well bonded into the external walls in alternate courses, and the longitudinal withe may also be bonded in either by cutting bricks as at A, or by mitreing as at B.
In ordinary buildings the external walls of chimneys and chimney breasts are, for economy, made only half a brick thick throughout, both inside the building and above the roof. Examples of the necessary bond are therefore shown in Figs. 69, 70, though such thin external walls are objectionable for the reasons already stated.
Fig. 70. Chimney. Half-brick external walls. Stretching Bond.
These 4½-inch external walls are sometimes built in stretching bond ; such a bond, however, carried out in the ordinary manner, leaves the cross withes quite detached from the side walls, as are the withes A B in Fig. 70.
This may, however, be avoided by causing the withes in alternate courses to penetrate the side walls to the depth of ¼ brick or 2¼ inches, as shown in withes C C, D D, Fig. 70, or by cutting the bricks forming the ends of the withes to a mitre, as at E F, Fig. 69, so as to fit the adjacent bricks in the external wall, which are similarly cut.
The external walls of chimneys may very conveniently be built in Flemish bond as shown in Figs. 71,72. It will be noticed that there is no elaborate cutting of bricks, the bond is perfectly symmetrical, and the withes are admirably united with the external walls.
If the flues at one end were required to be 14 inches square, as for a very large kitchen chimney, ¾ bricks would be used instead of c c, and half bricks or false headers inserted at h h.
The exact arrangement of bond in a chimney must depend upon the size, shape, diameter, and arrangement of the flues, the thickness of the outer walls, the bond adopted in the building, and other particulars depending upon circumstances.
It would of course be impossible to illustrate even a very small portion of the various arrangements required by different combinations of the above particulars.
Fig. 72. Chimney. Half-brick external walls. Flemish Bond.
Further examples cannot here be given, but it will be good practice to the student to draw for himself the bonds best adapted for chimneys of different forms and arrangements, in doing which it is hoped that he will find the above illustrations a useful guide.