Par. 20. - Portland Cement Mortar. - Portland cement mortar shall be thoroughly mixed and made of one part Portland cement and not more than three parts of sand by volume. Lime putty, or hydrated lime, may be added to an amount equal to fifteen per cent of the volume of the cement.

Par. 21. - Concrete. - Concrete shall mean an approved mixture of Portland cement, water and fine and coarse aggregate.

Par. 22. - Mixing. - The ingredients shall be thoroughly mixed and the mixing shall continue until the cement is thoroughly distributed and the mass is uniform in color. For reinforced concrete the consistency shall be such that the concrete will entirely enclose the reinforcement, but shall not be so wet as to cause separation of the ingredients.

Par. 23. - Rubble Concrete. - Rubble concrete shall mean an approved mixture of Portland cement, water, fine and coarse aggregate to which stones are added after depositing. When one-man stones are used to form rubble concrete, there shall be not less than three inches between the stones and the forms, and between edges of adjacent stones. When stones larger than one-man size are used to form rubble concrete there shall be not less than six inches between the stones and forms, and between edges of adjacent stones. Stones shall be clean and wet and shall be deposited in concrete already in place, before the latter has begun to set.

Par. 24. - In piers no stone shall be larger than one quarter of the horizontal cross section of the pier. Rubble concrete shall not be used for any projecting footing.

Par. 25. - Joints. - Joints formed between portions of concrete placed at different times shall be made in such a manner as not to weaken the completed structure. Whenever fresh concrete joins concrete which is set, or partly set, the surface of the old concrete shall be rough, clean and thoroughly wet.

Par. 26. - Use of Concrete. - Concrete shall be used immediately after mixing, it shall not be placed in the work after it has begun to harden, and it shall be deposited in such manner and under such regulations as to secure a compact mass of the best quality for the proportions used. Forms shall remain until the concrete has hardened sufficiently to carry its load safely, and shall be removed without damage to the concrete.

Par. 27. - Inspection of Concrete. - The commissioner may require an applicant for a permit for the structural use of concrete to have a competent inspector, satisfactory to the commissioner, at all times on the work while concrete is being mixed, or deposited and such inspector shall make daily reports to the commissioner on the progress of the work.

Par. 28. - Steel. - Steel for all structural work in buildings, except reinforced concrete work, shall conform to the requirements of the Standard Specifications for Structural Steel for Buildings of the American Society for Testing Materials, as from time to time revised.

Par. 29. - Wrought Iron. - Wrought iron for structural work in buildings shall conform to the requirements of the Standard Specifications for Wrought Iron Plates, Class B of the said society as from time to time revised.

Par. 30. - Cast Iron. - Cast iron for all structural work in buildings shall conform to the requirements of the Standard Specifications for Medium Gray Iron Castings of the said society as from time to time revised.

Par. 31. - Cast Iron Columns. - Cast iron columns shall not be used in the structural frames of buildings whose height exceeds two times the least width of base, nor in any building over one hundred feet high. Cast iron columns shall be faced at ends to a true surface perpendicular to the axis to give full bearing for the cross section of the column.

Par. 32. - All hollow cast iron columns, except when open at both ends and without flanges, shall have two three eighths of an inch holes drilled on the top or bottom side of the column as cast, if the columns are cast on side one hole about twelve inches each side of the center of the length of the column, to exhibit thickness of the shell. Columns cast on end shall have two three eighths of an inch holes drilled, at an angle of ninety degrees to each other at the middle of the column, to exhibit thickness of shell. Additional holes shall be drilled when required by the commissioner.

Par. 33. - Cast Iron Bases and Lintels. - Cast iron bases or shoes shall be planed on top. Bases which rest on structural steel members shall be planed top and bottom. The thickness of metal shall be not less than one inch. The inclination of the outer edge of the ribs with the horizontal shall be not less than forty-five degrees. Whenever a side of the bed plate exceeds three feet in length a reinforcing flange at least three inches high shall be provided along such edge of the plate.

Par. 34. - Cast iron lintels shall be not less than three fourths of an inch in thickness and shall not be used for spans exceeding six feet.

Par. 35. - Timber. - All timber for structural purposes shall conform to such specifications as may be promulgated by the commissioner but shall be free from defects such as injurious ring or round shakes, and through shakes that extend to the surface, from unsound and loose knots, and knots in groups that will materially impair the strength, rot, worm holes and defects caused by manufacture.

Par. 36. - Classes of Timber. - "Dense" and "sound" classes of timber shall be as defined by the American Society for Testing Materials in their Standard Definitions of Terms relating to Structural Timbers, section three, as revised in nineteen hundred and fifteen.

Strength of Materials

Par. 37. - Piers. - Any body of masonry less than four feet long in its greatest horizontal dimension shall be called a pier. The height of a pier between openings having a continuous wall above or below them shall be assumed equal to the height of the opening. The height of a pier or wall supporting floors or roofs shall be assumed as the distance from top of footing or floor to under side of floor or roof beams.