Among the main requirements of usual practice are these: that the depth of stretchers shall be from one to one and one-half times the rise of the course; that the length shall be not less than two times the rise; that for headers the least dimension shall be the rise, and the length 4 ft. to 5 ft. Sometimes headers are specified in each course, sometimes only in alternate courses. Whether headers occur in each or in alternate courses the spacing should be three or four (depending on length) stretchers between headers. The bond, namely, the distance along a horizontal joint between vertical joints on opposite sides of it, is usually specified to be not less than a certain amount, often 12 in., although this may properly vary with rise of course.
If the rise of the courses is not uniform throughout, appearance of the face as a whole requires that no course should be laid upon or over a course of less rise; also that the decrease in rise should be gradual and uniform. There may be other minor requirements some of which come within the usual understanding of masons and inspectors as to what constitutes "good practice" or "workmanlike manner." There are also many ways of wording clauses of specifications in order to secure work of the character outlined by the foregoing main requirements. For instance, we may specify that a certain percentage of the face area shall be headers. While each of these clauses may be admirable in itself, a combination of them should be scrutinized carefully to see that they do not conflict, or that they are not unnecessarily restrictive. In other words, in any specifications whatsoever, specify the desired standard with as few clauses as possible, and see that they do not conflict nor specify two things.
A case in point was the specification for the upstream face work of a recent important dam. Apparently all the clauses that occurred to the writer of the specification, each of them unobjectionable and often to be met with, had been so combined that if all had been literally and exactly observed, the builder would have been limited to two sizes of stone (a stretcher and a header) in the entire face. In reality the quality of work which the writer had in mind would have permitted quite a departure from such a standard. Such a combination of clauses leaves a prospective bidder in doubt as to how many and which clauses are to be enforced, and can but have a marked adverse effect upon the price bid. This is especially true when it is proposed to obtain the face stone from a still unopened quarry in connection with the dam.