At the meeting of the National Cement Users' Association already referred to, the Committee on Sidewalks, Floors, and Streets recommended the following specifications for the top coat: "Three parts high-grade Portland cement and five parts clean, sharp sand, mixed dry and screened through a No. 4 sieve. In the top coat, the amount of water used should be just enough so that the surface of the walk can be tamped, struck off, floated, and finished within 20 minutes after it is spread on the bottom coat; and when finished, it should be solid and not quaky." In the January, 1907, number of Cement, Mr. Albert Moyer, Assoc. M. Am. Soc. C. E., discussing the subject of cement sidewalk pavements, gives specifications for monolithic slab for paving pur poses. For an example of this construction, he gives the pavement around the Astor Hotel, New York: "As an alternative, and instead of using a top coat, make one slab of selected aggregates for base and wearing surface, filling in between the frames concrete flush with established grade. Concrete to be of selected aggregates, all of which will pass through a i-inch mesh sieve; hard, tough stones or pebbles, graded in size; proportions to be 1 part cement, 2+ parts crushed hard stone screenings or coarse sand, all passing a I-inch mesh, and all collected on a +-inch mesh. Tamped to an even surface, prove surface with straight edge, smooth down with float or trowel, and in addition a natural finish can be obtained by scrubbing with a wire brush and water while con crete is 'green,' but after final set."
250. Seasoning. The wearing surface must be protected from the rays of the sun by a covering which is raised a few inches above the pavement so as not to come in contact with the surfaces. After the pavement has set hard, sprinkle freely two or three times a day for a week or more.
251. Cost. The cost of concrete sidewalks is variable. The construction at each location usually requires only a few days work; and the time and expense of transporting the men, tools, and ma terials make an important item. One of the skilled workmen should be in charge of the men, so that the expense of a foreman will not be necessary. The amount of walk laid per day is limited by the amount of surface that can be floated and troweled in a day. If the surfacers do not work overtime, it will be necessary to stop concreting in the middle of the afternoon, so that the last concrete placed will be in con dition to finish during the regular working hours. The work of con creting may be continued considerably later in the afternoon if a dryer concrete is used in mixing the top coat, and only enough water is used so that the surface can be floated and finished soon after being placed. The men who have been mixing, placing, and ramming concrete can complete their day's work by preparing and ramming the founda tions for the next day's work.
The contract price for a well-constructed sidewalk 4 to 5 inches in thickness, with a granolithic finish, will vary from 15 cents to 30 cents per square foot.