ASHLAR MASONRY.
20. Stone. The stones shall be large and well-propdrtioned.
21. Courses shall not be less than fourteen inches (14') or more than thirty inches (30") thick, thickness of courses to diminish regularly from bottom to top.
22. Dressing. Beds and joints or builds of face stone shall be fine-pointed, so that the mortar layer shall not be more than one half inch (r) thick when the stone is laid.
23. 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 twelve inches (12').
24. Exposed surfaces of the face stone shall be rock-faced, and the edges shall be pitched to true lines and exact batter. The face shall not project more than three inches (3') beyond the pitch line.
25. Chisel drafts one and one half inches (1}") wide shall be cut at exterior corners.
26. Holes for stone hooks shall not be permitted to show in exposed surfaces. Stone shall be handled with clamps, keys, Lewis, or dowels.
27. Stretchers. Stretchers shall not be less than four feet (4') long and have at least one and a quarter times as much bed as thickness of course.
28. Headers. Headers shall not be less than four feet (4') long, shall occupy one fifth of face of wall, shall not be less than eighteen inches (181 wide in face, and, where the course is more than eighteen inches (18') high, width of face shall not be less than height of course.
29. 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.
30. Headers in face and back of wall shall interlock when thickness of wall will admit.
31. Where the wall is three feet (3') thick or less, the face stone shall pass entirely through. Backing shall not be allowed.
32a.* Backing. Backing shall be large, well-shaped stone, roughly bedded and jointed; bed joints shall not exceed one inch (1"). At least one half of the backing stone shall be of same size and character as the face stone and with parallel ends. The vertical joints in back of wall shall not exceed two inches (2'). The interior vertical joints shall not exceed six inches (6"). Voids shall be
thoroughly filled with concrete or spans fully bedded in cement mortar.
32b.* Backing shall be of concrete or headers and stretchers, as specified in paragraphs S8-30, and the heart of the wall shall be filled with concrete.
33. Where the wall will not admit of such arrangement, stone not lees than four feet (4') long shall be placed transversely in the heart of the wall to bond the opposite sides.
34. Where stone is backed with two courses, neither course shall be lees than eight inches (8") thick.
35. Bond. The bond of stone in the face, back, and heart of the wall shall not be less than twelve inches (12"). The backing shall be laid to break joints with the face stone and with one another.
36. Coping. Coping stones shall be full size throughout, of dimensions indi cated on the drawings.
37. Bed*, joints and top shall be fine-pointed.
38. Location of joints shall be determined by the position of the bed plates, and be indicated on the drawings.
39. Cramps. Where required, coping stone, stone in the wings of abut ments, and stone on piers shall be secured together with iron cramps or dowels, their position being indicated on the drawings.
B. For Arches.
40. Arch Stones. Voussoirs shall be full size throughout and dressed true to templet, and shall have bond not Less than thickness of stone.
41. Joints of voussoirs and intrados shall be fine-pointed. Mortar joints shall not exceed three eighths inch (1").
42. Exposed surfaces of the ring stone shall be smooth or rock faced with a marginal draft. • 43. Number of courses and depth of voussoirs shall be indicated on the drawings.
45. Backing. Backing shall consist of concrete or large stone shaped to fit the arch, bonded to the spandrel and laid in full bed of mortar.• 46. Where waterproofing is required, a thin coat of mortar or grout shall be applied evenly for a finishing coat, upon which shall be placed a covering of approved waterproofing material.
47. Centers shall not be struck until directed by the engineer.
48. Bench Walls, etc. Bench walls, piers, spandrels, parapets, wing walls, and copings shall be built under the specifications for Ashlar for Bridges and Retaining Walls.