This section is from the book "Cyclopedia Of Architecture, Carpentry, And Building", by James C. et al. Also available from Amazon: Cyclopedia Of Architecture, Carpentry And Building.
The wearing surface usually consists of 1 part Portland cement and 2 parts crushed stone or good, coarse sand, all of which will pass through a 1/4-inch mesh screen - thoroughly mixed so as to secure a uniform color. This mixture is then spread over the concrete base to a thickness of one inch, this being done before the concrete of the base has set or become covered with dust. The mortar is leveled off with a straight edge, and smoothed down with a float or trowel after the surface water has been absorbed. The exact time at which the surface should be floated depends upon the setting of the cement, and must be determined by the workmen; but the final floating is not usually performed until the mortar has been in place from two to five hours and is partially set. This final floating is done first with a wooden float, and afterwards with a metal float or trowel. The top surface is then cut directly over the cuts made in the base, care being taken to cut entirely through the top and base all around each block. The joint is then finished with a jointer, Fig. 80, and all edges rounded or beveled. Care should be taken in the final floating or finishing, not to overdo it, as too much working will draw the cement to the surface, leaving a thin layer of neat cement, which is likely to peel off. Just before the floating, a very thin layer of dryer consisting of dry cement and sand mixed in the proportion of one to one, or even richer, is frequently spread over the surface; but this is generally undesirable, as it tends to make a glossy walk. A dot roller or line roller, Figs. 81 and 82, may be employed to relieve the smoothness.
Fig. 80. Jointers.
Fig. 81. Brass Dot Roller.
Fig. 82. Brass Line Roller.
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 purposes. 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 3/4-ineh mesh sieve; hard, tough stones or pebbles, graded in size; proportions to be 1 part cement, 2 1/2 parts crushed hard stone screenings or coarse sand, all passing a 3/4-inch mesh, and all collected on a 1/4-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 concrete is 'green,' but after final set."
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.
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 materials 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 condition to finish during the regular working hours. The work of concreting 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 foundations for the next day's work.