The average size of bricks in this country is a fraction under 9 in. long and 2 1/2 in. thick; and, in consequeuce of this uniformity of size, a wall of this material is described as of so many bricks in thickness, or of the number of inches which result from multiplying 9 in. by any number of bricks - a 9-in., or 1-brick wall; a 14-in. wall, or 1 1/2 brick (13 1/2 in. would be more correct, in fact; for, although a joint of mortar must occur in this thickness, yet the fraction under the given size of the brick is enough to form it); 18 in., or 2 bricks, and so on. The great art in bricklaying is to preserve and maintain a bond, to have every course perfectly horizontal, both longitudinally and transversely, and perfectly plumb, which last, however, may not mean upright, though that is the general acceptation of the term, for the plumb rule may be made to suit any required inclination, as inward, against a bunk, for instance, or in a tapering tower, and also to make the vertical joints occur perpendicularly over each other; this is vulgarly and technically called keeping the perpends.

By bond in brickwork is intended that arrangement which shall make the bricks of every course cover the joints of those in the course below it, and so tend to make the whole mass or combination of bricks act as much together or dependency upon one another as possible. A brick, being exactly half its length in breadth, it is impossible, commencing from a vertical end or quoin, to make a bond with whole bricks, as the joints must of necessity fall one over the other. This difficulty is obviated by cutting a brick longitudinally into 2 equal parts, which are called half headers. One of these is placed next to a whole header, inward from the angle, and forms with it a § length between the stretchers above and below, thus making a regular overlap, which may then be preserved throughout. Half headers, so supplied, are technically termed closers. A 3/4 stretcher is obviously as available for this purpose as a 1/2 header, but the latter is preferred, because, by the use of it, uniformity of appearance is preserved, and whole bricks are retained on the returns.

In walls of almost all thicknesses above 9 in., to preserve the transverse and yet not destroy the longitudinal bond, it is frequently necessary to use half bricks; but it becomes a question whether more is not lost in the general firmness and consistence of the wall by that necessity than is gained in the uniformity of the bond. It may certainly be taken as a general rule, that a brick should never be cut if it can be worked in whole, for a new joint is thereby created in a construction, the difficulty of which consists in obviating the debility arising from the constant recurrence of joints. Great attention should be paid to this, especially in the quoins of buildings in which half bricks most readily occur, and there it is not only of consequence to have the greatest degree of consistence, but the quarter bricks used as closers are readily admitted, and the weakness consequent on their admission would only be increased by the use of other bats or fragments of bricks.

Another mode of bonding brickwork is, instead of placing the bricks in alternate courses of headers and stretchers, to place headers and stretchers alternately in the same course. This is called Flemish bond. Closers are necessary to both varieties of bond in the same manner and for the same purpose; half bricks will also occur in both, but what has been said in reference to the use of them in the former applies even with more force to the latter, for they are more frequent in Flemish than English, and the transverse tie is thereby rendered less strong. Their occurrence is a disadvantage which every pains should be taken to obviate. The arrangement of the joints, however, in Flemish bond, presenting a neater appearance than the English bond, it is generally preferred for external walls when their outer faces are not to be covered with stucco or plaster composition of any kind, but English bond should have the preference when the greatest degree of strength and compactness is considered of the highest importance, because it affords a better transverse tie than the other. It is a curious fact, that what is known in England as the Flemish bond, in brickwork, is unknown in Flanders, and is practised in the British Isles alone.

In Flanders, Holland, and Rhenish Germany, which are all bricklaying countries, no kind of bond is found but what is known in England a English bond.

It has been attempted to improve the bond in thick walls by laying raking courses in the core between external stretching courses, and reversing the rake when the course recurs. This obviates whatever necessity may exist for using half bricks in the heading courses, but it leaves triangular interstices to be filled up with bats. Skilful and in nious workmen are well aware of the necessity of attending to the bond, and are ready both to suggest and to receive, and practise an improvement; but generally the workmen themselves are both ignorant of its importance and careless in preserving it, even according to the common modes. Their work should, therefore, bo strictly supervised as they proceed with it, for many of the failures which are constantly occurring may be referred to their ignorance or carelessness in this particular.

Not second in importance to bonding in brickwork is that it be perfectly plumb or vertical, and that every course be perfectly horizontal or level, both longitudinally and transversely. The lowest course in the footings of a brick wall should be laid with the strictest attention to this latter particular; for, the bricks being of equal thickness throughout, the slightest irregularity or incorrectness in that will be carried into the superimposing courses, and can only be rectified by using a greater or less quantity of mortar in one part or another; so that the wall will, of course, yield unequally to the superincumbent weight, as the work goes on, and perpetuate the infirmity. To save the trouble of keeping the plumb rule and level constantly in his hands, and yet to ensure correct work, the bricklayer, on clearing the footings of a wall, builds up 6 or 8 courses at the external angles, which he carefully plumbs and levels across, and from one to the other. These form a gauge for the intervening parts of the courses, a line being tightly strained from one end to another, resting on the upper and outer angles of the gauge bricks of the next course to be laid, and with this he makes his work range.

If, however, the length be great, the line will, of course, "sag," and it must, therefore, be carefully set and propped at sufficient intervals. Having carried up 3 or 4 courses to a level with the guidance of the line, the work should be proved with the level and plumb rule, and particularly with the latter at the quoins and reveals as well as on the face. A smart tap with the end of the handle of the trowel will generally suffice to make a brick yield what little it may be out while the work is so green, and not injure it. Good workmen however, take a pride in showing how correctly their work will plumb without tapping. To work which is circular in the plan, both the level and the plumb rule must be used, together with a gauge mould or a ranging trammel, to every course; as it must be evident that the line cannot be applied to such in the manner just described. To every wall of more than 1 brick thick 2 men should be employed at the same time, one outside and the other in; one man cannot do justice from one side even to a 14-in. wall.

Inferior workmen and apprentices are generally employed as inside men, though the work there is of quite as great importance as exteriorly, except for neatness, and for that only it the brickwork is to show on the outside.