[BRICK BONDS]
Bond in brickwork is the overlapping of the brick one upon the other, either along the length of the wall or through its thickness, in order to bind them together into a secure structural mass. It is true, mortar is used to cement the brick together into a monolithic whole, but the real bond is the overlapping of the brick which the mortar serves to maintain. Units are shifted back and forth so that the vertical joints in two successive layers or "courses" do not come into line; in other words, the brick are laid so as to break joint, the whole forming a natural bond or a structural unity giving strength to the wall.
The strength and rigidity of a wall due to this bonding are clearly shown in [Fig. 46]. A concentrated load at any point on the wall is thus distributed over a larger area as indicated by the dotted arrows.
Fig. 46. Bonding Strength
Stretcher and Header
In speaking of brick bond, two terms are constantly recurring, viz., "stretcher" and "header." When a brick is laid lengthwise of the wall, thus showing its long, narrow dimension or "face" on the surface, it is called a stretcher. If its length extends back into the wall, so that its short dimension shows on the surface, it is called a header. The stretcher secures strength in the length of the wall. The header serves to form the transverse bond, that is, the strength of the wall through its thickness. When a brick is broken, as the case may require, the fragment is called a "bat." Bats are used either simply to fill in; or, as definite sized pieces, cut and used to make the bond come out right, in which case they are called "closures." While at certain points of the wall bats may be necessary, they should be sparingly used and then only according to the best practices of the craft.
Design in Bonds
In the old days, and indeed up to comparatively recent times, brick bond was used only in a structural or natural way, that is, to secure the strength of the wall as a solid mass; but in the seventeenth century European builders began to see an artistic possibility in the bond as it appeared on the surface. They began to see the fine tracery of the mortar joint running over the background of the brick, which could be varied into attractive patterns by different arrangement of the brick bond. As a consequence, there have been developed, in the main, three different types of bond, Running or Stretcher, English, and Flemish, which are used at the present day, with various modifications, to secure attractive effects in pattern.