This section is from the book "A Practical Treatise On The Joints Made And Used By Builders", by Wyvill J. Christy. Also available from Amazon: Practical treatise on the joints made and used by builders.
This lies between the courses, or between the bottom course and the bearing stratum, and is that on which almost every part of a construction rests. It is exposed to perpendicular pressure, for the better distribution of which plates or templates are built in to afford spreading bearing surfaces to carry girders, joists, etc. Sleepers, lintels, plates, and templates, wood bricks, and bond timber are generally bedded in mortar, window and door frames in lime and hair or cement, and wood slips dry. Most of these depend to a great extent upon the quality of their bed joints, both for their own firmness and for the degree of shakiness they impart to a building. In foundations where parts start from different levels, those brought up from the lowest should have close joints, or be built in cement or hard-setting mortar to secure an equality of settlement, and in all cases footings should be carefully bedded so as to afford a solid and unyielding base. Iron columns, girders, or pilasters built into brickwork require sound York, or other hard bedstones or templates of a thickness equal to two or more courses, and of as many feet super as convenient to get a wide bearing the full width of the wall. These must be tooled true and dressed fair on the top to take the ironwork, and solidly bedded with full square beds perfectly level in good mortar or cement; and if any perforation, or sinking, or joggling is required for snug, or corking, or flange on column, or rivet on girder, or if any dowel is to be leaded into the template to fit into a slot in the girder, it should be done before bedding the stonework. Girders carrying brickwork are sometimes covered with a course of hard flagstones bedded in cement of the width of the intended wall. In the same way the caps of columns and pilasters must be truly fitted in a workmanlike manner to overhead stone blocks or landings dressed fair and mortised for corkings. Heavy timbers are secured to brickwork by building in stones pierced with countersunk holes for the reception of bolts with heads downwards every few feet, the shanks being built in as the work proceeds, and the timber bolted thereto with countersunk nuts and washers at the proper level. Ironwork bedded or inserted in brickwork does not injure it. In all cases when new work is bedded on old, the latter must be brushed and well wetted before spreading the mortar.
Birdsmouth is any re-entering angle notched out of a brick by way of a moulded ornament, or it is a similar notch required for an inside joint; as, for example, when a wall does not return square in the case of a skew or squint quoin, as in Fig. 1.
This is tantamount to a broken joint, since bricks to form bond must be laid with systematic lapping, so that no two vertical joints in adjacent courses can appear in the same straight line, because they do not in fact lie in the same plane. In the same course, however, the cross or transverse joints need not be broken, for work to be well bonded only requires the vertical joints to be well covered by the superimposed bricks. Owing to straight cross joints, however, not always being considered sufficiently weatherproof, some break them, and thus abstract from the work a certain amount of longitudinal tie. As the only condition exacted by bond is the discontinuance of the vertical joints of each course at the rising one, there are, as might be expected, several ways of arranging bricks by which this requirement can be more or less perfectly fulfilled. Amongst many varieties of bond made use of the following may be noticed as the most generally adopted.
Angle bond occurs at skew quoins or oblique angles requiring cut bricks and offering great temptations to hide very rough cutting with flushing. It may be here observed, that in order not to leave voids, closers of some shape or other are required to get the lap in all bonds. They should never be set at a less distance than half a brick from any opening or quoin. Chimney bond consists of nothing but stretchers, and is therefore only half a brick in thickness. Diagonal bond is useful for maintaining longitudinal strength in a thick wall, and consists of ordinary face work with a hearting laid raking or diagonally at an angle sufficient to admit the bricks without snapping, as shown in Fig. 2. English, or as it is often called old English bond, and sometimes King's bond, presents on each face a course of headers alternating with a course of stretchers. Here, obviously, it is practicable to vary the arrangement by having two, three, or more courses of headers to one of stretchers, still maintaining an excellent bond. Flemish bond shows on each face a series of courses each formed with alternate headers and stretchers. Garden wall, or running bond, Fig. 3, consists of one header to three stretchers on each face and every course, the headers of each course being in the centre of the stretchers of the adjacent courses. Heading bond is made up of courses of headers only. Herring-bone bond resembles diagonal bond excepting that the hearting is laid in the direction of both diagonals. To these may be added cement bond noticed under Cement Joint, and hoop iron bond, which does not consist of any particular arrangement of bricks, though its province is to obtain longitudinal strength, which is the boast of old English. This bond is formed by building in about every twelfth course one row at least of 1½ in. hoop iron tarred and sanded to each half-brick of thickness. A 14 in. wall would therefore have three parallel rows. The hoop iron must be properly bent, lapped, and hooked at junctions, and wherever necessary to maintain the tie. It is often bedded in cement. Tyerman's patent variety is much used, having a good grip through each edge being notched at intervals into vertical teeth in opposite directions. When brickwork is very thick the faces are laid in the approved bond and the interior is filled in by larrying, which consists in spreading a thick bed of mortar and pushing each brick along it into position, by which means all become snugly bedded and their sides well surrounded with mortar. The cross bond of hollow walls is necessarily imperfect, the 2¾ in. or so hollow space being crossed by iron ties either wrought, galvanised, or cast, built in every fourth course excepting near the openings, quoins, and angles, where they should be placed every alternate course. Their usual horizontal distance apart is about 18 in., and no mortar or rubbish must be allowed to rest upon them.