Sidewalks may be made of flagstones, concrete, or brick. A flag is a thin slab of stone, which is generally used in sidewalk work. Concrete sidewalks are usually finished on top with cement and sand. The bricks used for sidewalk work should be hard and of the variety known as paving brick.
Stone Sidewalks - If stone of a texture that readily splits into flags can be obtained, it will probably make a better and cheaper sidewalk than will concrete. A flag sidewalk can be taken up and relaidbetterthan one of concrete, is easier to repair, and is also more durable.
The stone for sidewalks should be 2 or 3 inches thick when used in areas or similar places, and the flags should be cut rectangular. They should be laid on a sand or cinder bed that is 2 or 3 inches in thickness. The edges of the stones usually rest on a small bed of concrete, or 1-to-1 cement mortar is put into the cracks as shown at c, Fig. 65. In this way is obtained a joint that will prevent water from soaking down between the flags and freezing. In countries where there is no frost, this concrete and cement may be omitted, and the sidewalk may simply be laid on the sand bed.
Sidewalks located between the curb and the building line are subjected to more traffic than pavements found in areas, etc. and should therefore be built in a more substantial manner. The flags used for this class of sidewalks are generally 3 or 4 inches thick. It is always best, if possible, to have the stones of the
same width as the sidewalk, but for wide sidewalks, this is impracticable. When there is danger of frost getting under the sidewalk and thus causing it to heave, the flags should be supported at the ends only, as shown in Fig 66. A 12 inch dwarf wall should be built at the curb line, as shown at a, and carried below the frost line. The curbstone b is from 4 to 6 inches thick, and is rabbeted into the dwarf wall. At c is shown the gutter, and d, the stone pavement, which is supported at its center by a dwarf wall e. If the sidewalk is laid in two courses, or if it extends to the building line, it may rest on a break in the foundation wall f, as shown. Under the sidewalk at g is a bed of sand or ashes.
Brick Sidewalks - In constructing brick sidewalks, good, hand paving bricks, sound and square, should be used. These bricks should be laid flat, herring-bone fashion, on a bed of sand that is from 4 to 6 inches thick. After the bricks are laid and graded, the entire surface should be covered with sand, which is swept over the bricks until the joints are thoroughly filled. If extra thickness of wearing surface is desired, the bricks may be set on edge, and covered with sand as described.
Cement Sidewalks - The method of laying cement sidewalks is as follows: The ground should be leveled off from 12 to 15 inches below the finished grade of the walk, and should be well settled by ramming, care being taken that the excavation is drained to one side. A foundation consisting of about 8 or 10 inches of coarse gravel, stone chips, sand, or cinders, should then be laid and well tamped or rolled with a heavy roller. An attempt often is made to economize on this kind of foundation by making it only 5 or 6 inches thick. However, foundations of such thickness generally allow the frost to penetrate to the ground and heave up the pavement in spots.
After the foundation has been rolled, the concrete should be prepared in the proportion of 1 part of cement, 3 parts of sand, 5 parts of broken stone, and a sufficient quantity of water to make a stiff mortar. It should be thoroughly mixed and worked while being laid. The top, or finishing, coat should be laid immediately, and only as much concrete should be laid as can be covered with cement on the same day, because if the concrete gets dry on top, the finishing coat will not adhere to it. The top coat should be prepared by mixing 1 part of the best Portland cement with 2 parts of fine sand or 2 parts clean, sharp, crushed granite or flint rock.
A 1/2 inch space should be left between the curb and the pavement and between the building line and the pavement to allow for expansion and contraction. This space should be filled with cinders or ashes. the pavement itself should be laid off into blocks 6 feet square or less. These blocks should be separated from one another by sheets of tar paper, which should extend all the way through the concrete. It is very essential that grooves be made with a trowel in the top coat directly over the tar paper, so that if the concrete cracks while drying out, it will be sure to part in these grooves and not in the body of the pavement.
Hair Cracks are often caused by the mortar in the hot coat being too rich in cement. If the pavement is troweled too much, it has a tendency to make the cement float to the top. This is as liable to cause hair cracks as the use of too much cement. If the top coat is put on too wet, it has the same effect.
In many cities, the law requires that concrete sidewalks be finished with a rough surface. Such a surface is not so slippery in winter as a smooth finish. It also possesses the additional advantages that it is easier to construct and does not show any hair cracks. In laying such a surface, the top coat is leveled with a straightedge running on battens, one set on each side of the walk. The battens are arranged so that the part of the walk at the curb will be lower than the part at the building wall. (this patch is controlled by city ordinances, and is usually 4 inches in 10 feet for all sidewalks.) The sidewalk is then left until it has almost set, before it is troweled. It should be troweled as little as possible, and with a wooden trowel instead of one made of steel. After trowleling, it should be covered with straw and kept moist for at least a week. the less the sidewalk is smoothed, with a straightedge or trowel, and the more it is rammed, instead, the better it will be.
Fig 67 shows a section of a concrete sidewalk, the ashes or spalls being shown at a,the first coat of concrete, at b; the finishing coat, at c'; the street paving, at d'; and the joints with tar paper in them, at c.