The rolling required with either a, gravel or broken-stone founda tion can best be done with a 'steam roller, which is only an additional reason for specifying that the subgrade shall be rolled with a steam roller. Although it is a little out of place here, this is the most con venient place to say that a steam roller is also much better than a horse roller for rolling the brick. If the subgrade, and the gravel or broken stone foundation, and the brick are all rolled with a steam roller, the cost of rolling any one of these is materially lessened, since the roller is thus used a greater part of the time.
Brick—The first brick pavements were laid on a foundation consist ing of a layer of gravel and a course of brick laid flatwise. This form of foundation has been abandoned for two reasons: first, because some other form is usually cheaper; and second, because of the lack in the past of proper precautions in laying this form of foundation. There have been two defects in constructing this form of foundation. First, the gravel is neither spread nor consolidated uniformly. The proper method of spreading and rolling the gravel has been described above under the head Gravel. The second defect consists in laying broken bricks with their broadest side up, and hence the space below is not well filled while the cushion coat is being spread, and consequently after the pavement is completed the cushion coat works into these cavities and permits the surface of the pavement to sink. If all broken brick are laid on the broad side and care be taken thoroughly to fill the joints while laying the cushion coat, this form of foundation will give satisfaction, even though the lower course of brick be quite in ferior. The writer is quite familiar with a piece of such pavement laid on a very unfavorable subgrade, but with proper precautions in the two respects mentioned above, which for ten or fifteen years has given entire satisfaction and has as good a surface as adjoining pavements on a con crete base, even though the latter are on a more favorable subgrade and carry less travel. This pavement illustrates a rule of construction that can not be repeated too often, viz.: No good brick pavement can be constructed without proper attmtion to all details.
The cushion is a layer of sand 1 to 2 inches thick between the founda tion and the wearing course of brick, to secure a uniform bed or bearing for the brick. Unless the bricks or blocks are unusually uniform, the cushion layer should be 2 inches thick. • The thickness should be as uniform as possible so that the bricks will settle evenly during the rolling; and therefore the top of the concrete foundation should be carefully finished with a surface parallel to the surface of the pavement. Not infrequently loose fragments of stone are left on the surface of the concrete, a result which is very undesirable, since they necessitate a thicker cushion and at best prevent the bricks from coming to a uniform bearing. With good workmanship in laying
the concrete, there will be no loose pieces of stone on the surface; and if they do happen to get there, they should be removed before laying the cushion coat.
The sand for the cushion should preferably be so fine as to be of a soft, velvety nature, and should contain no pebbles of any considerable size, or loam or vegetable matter. The size of pebbles permissible de pends upon the thickness of the sand bed. Pebbles will prevent the brick from having a uniform bearing; the loam is likely to be washed to the bottom of the layer and cause the brick to settle; while the vege table natter will decay or wash away, and leave the brick unsupported.
The spreading of the sand should be carefully done, so as to secure a uniform thickness and to have its upper surface exactly parallel to the top of the finished pavement. After the sand has been distributed approximately to the proper thickness with a shovel, the surface should be leveled by drawing over it a template conforming exactly to the curvature of the cross-section of the proposed surface of the pavement. The template should be drawn slowly over the sand bed several times, any depressions that develop being filled by sprinkling sand into them with a shovel. A considerable quantity of sand should be drawn along in front of the template, as this aids materially in packing the bed. It is necessary to draw the template several times to pack the sand well, particularly if there are wet and dry spots, as the successive jarring of the sand grains causes them to settle more closely together. When the sand cushion is properly packed it will have a uniform, smooth, velvety appearance, and will not look rough, porous and grainy.
The surface of the cushion layer is often prepared with a short lute; but the template secures a more uniform surface and also gives a greater compression and more even bed. With hand luting the surface of the pavement is almost certain to be covered with saucer-like depressions after it has been rolled. Hand luting should be prohibited except where the use of the template is impossible, as around man-hole covers, at street intersections, etc.