BRIDGE A D RETAINING WALL MASONRY, ASIILAR STONE Bridge and Retaining Wall Masonry, Ashlar Stone.-20. The stone shall be large and well proportioned. Courses shall not be less than 14 inches or more than 3C inches thick, thickness of courses to diminish regularly from bottom to top.
Dressing.-21. Beds and joints or builds of face stone shall be fine-pointed, so that the mortar layer shall not he more than 1 inch thick when the stone is laid.
22. Joints in face stone shall be full to the square for a depth equal to at least one-half the height of the course, but in no case less than 12 inches.
Face or Surface.-23. Exposed surfaces of the face stone shall be rock-faced, with edges pitched to the true lines and exact batter. The face shall not pro ject more than 3 inches beyond the pitch lines. • 24. Chisel drafts 1; inches wide shall be cut at exterior corners.
25. Holes for stone hooks shall not be permitted to show in exposed surfaces. Stone shall be handled with clamps, keys, lewis, or dowels.
Stretchers.-26. Stretchers shall not be less than 4 feet long with at least one and a quarter times as much bed as thickness of course.
Headers.-27. Headers shall not be less than 4 feet long; shall occupy one fifth of face of wall; shall not be less than 16 inches wide in face; and where the course is more than 18 inches high, width of face shall not be less than height of course.
28. Headers shall hold in heart of wall the same size shown in face, so arranged that a header in a superior course shall not be laid over a joint, and a joint shall not occur over a header; the same disposition shall occur in back of wall.
29. Headers in face and back of wall shall interlock when thickness of wall will admit.
30. Where the wall is 3 feet thick or less, the face stone shall pass entirely through. Backing shall not be permitted
Backing.-31a. Backing shall he large, well-shaped stone, roughly bedded and jointed; bed joints shall not exceed 1 inch. At least one-half of the back ing stone shall be of the same size and character as the face stone and with parallel ends. The vertical joints in back of wall shall not exceed 2 inches. The interior vertical joints shall not exceed 6 inches.
Voids shall be throughly filled with concrete, or with spalls, fully bedded in cement mortar.
31b. Backing shall be of concrete, or of headers and stretchers, as specified in paragraphs 26 and 27, and heart of wall filled with concrete.
Paragraphs 31a and 31b are so arranged that either may be eliminated accord ing to requirements: 32. Where the wall will not admit of such arrangement, stone not less than 4 feet long shall be placed transversely in heart of wall to bond the opposite sides.
33. Where stone is backed with two courses, neither course shall be less than 8 inches thick.
Bond.—Bond of stone in face, hack, and heart of wall shall not be less than 12 inches. Backing shall be laid to break joints with the face stone and with one another.
Coping.-35. Coping stone shall be full size throughout, of dimensions indi cated on the drawings.
36. Beds, joints and top shall be fine-pointed.
37. Location of joints shall be determined by the position of the bed plates as indicated on the drawings.
Locks.-38. Where required, coping stone, stone in the wings of abutments, and stone on piers, shall be secured together with iron cramps or dowels, to the position indicated on the drawings.