Par. 1. - All materials shall be of such quality for the purposes for which they are to be used as to insure, in the judgment of the commissioner, ample safety and security to life, limb and neighboring property. The commissioner shall have power to reject all materials which in his judgment are unsuitable, and may require tests to be made by the architect, engineer, builder, owner or other interested persons. Any test thus required shall be made under the supervision or direction of the commissioner, and at the expense of the owner.

Par. 2. - Brick. - Brick may be of hard-burned clay, sand lime or cement and, except for nogging, fire-stopping and nonbearing or curtain walls not exposed to the weather, shall be hard and strong, of quality approved as satisfactory by the commissioner. Second-hand bricks shall be thoroughly cleaned before being used.

Par. 3. - Hard brick tested for approval shall develop an average ultimate compressive strength of three thousand pounds per square inch. Brick shall be tested flat-wise (half bricks permitted) and the average shall be taken on at least five samples, none of which must fall below twenty-five hundred pounds per square inch. The compressive strength of wet brick after forty-eight hours in water must be at least two thirds that of dry brick, except that, when the lower strength is above three thousand pounds per square inch, the loss in strength may be ignored.

Par. 4. - Before brick or other masonry materials are submitted to absorption tests, they shall be dried to practically constant weight at a temperature between two hundred and twenty-five and two hundred and fifty degrees Fahrenheit and shall not be fully immersed when placed in water.

Par. 5. - Terra Cotta Floor Tile. - Terra cotta floor tile, when tested on end and faced with Portland cement, shall give an average compressive strength of not less than twenty-five hundred pounds per square inch of net area. The average strength shall be computed from the results of tests of ten average tiles.

Par. 6. - Building Blocks. - The term "block" as used in this section shall mean any shape of brick or tile which forms a hollow or cellular wall.

Par. 7. - Concrete, hollow and two-piece building blocks shall be made of Portland cement and suitable aggregates in such proportion as to develop the following ultimate compressive strength at twenty-eight days, shall average one thousand pounds per square inch of gross sectional area of the block as used in the wall and shall not fall below seven hundred pounds per square inch in any test, when testing at least six ordinary samples. In case of hollow building blocks, the gross cross sectional area shall be considered as the product of the length by the width of the block. No allowance shall be made for air spaces of the block. The allowable working stress for such block shall not exceed one hundred pounds per gross square inch.

Par. 8. - Terra cotta building blocks shall be whole, sound and hard burned and shall develop an ultimate crushing strength per square inch of gross area of not less than twelve hundred pounds when tested with the cells placed vertically, and three hundred pounds with the cells placed horizontally.

Par. 9. - The allowable working stress for such blocks shall not exceed one hundred pounds and fifty pounds per gross square inch respectively.

Par. 10. - The absorption of building blocks to be used for bearing or enclosing walls shall not exceed twelve per cent in forty-eight hours as an average, or more than fifteen per cent in any case.

Par. 11. - Concrete Aggregates. - The fine aggregates shall be sand or crushed screenings passing a one fourth inch screen. The coarse aggregate shall consist of gravel, crushed stone, slag or cinders retained on a one fourth inch screen. Cinders or slag may be used for aggregate only for walls of one story buildings, for floor slabs, roof slabs, partitions, fireproofing, fire stopping and filling.

Par. 12. - Sand. - Sand or other fine aggregate for concrete shall be of such quality that mortar of one part Portland cement and three parts sand by weight shall show a tensile strength of not less than seventy per cent of the strength of mortar made on the same proportions with the same cement and standard Ottawa sand. If the tensile strength of such mortar is less than eighty per cent of that made with Ottawa sand, additional cement shall be used in such amount as may be required by the commissioner. The commissioner may require such tests when, in his judgment, they are necessary.

Par. 13. - Stone. - Stone for concrete shall be clean, hard and durable. For reinforced concrete it shall be of suitable size for the work and shall be small enough to allow the concrete to pass readily between and easily surround the reinforcement, and fill all parts of the forms.

Par. 14. - Gravel. - Run-of-bank gravel shall be used only when and as approved by the commissioner.

Par. 15. - Cinders and Slag. - Cinders shall be composed of hard, clean, vitreous clinkers, reasonably free from sulphides, unburned or partly burned coal and ashes. Slag shall be clean and hard. Cinders and slag shall be of suitable size for the work.

Par. 16. - Portland Cement. - Portland cement shall conform to the Standard Specifications of the American Society for Testing Materials as from time to time revised.

Par. 17. - Lime. - Lime shall be free from ashes, clinker and other foreign material and shall not be air slaked.

Par. 18. - Lime Mortar. - Lime mortar shall be made of slaked lime or hydrated lime with proper proportion of sand.

Par. 19. - Cement-Lime Mortar. - Cement-lime mortar shall be thoroughly mixed and made of one part Portland cement, not more than two parts slaked lime or hydrated lime and not more than eight parts of sand by volume, but mixtures with larger proportion of cement shall be allowed higher stress as hereinafter provided.