55. Sand Cushion.—The sand used for the cushion bed should be moderately coarse and must be fairly clean and pure. The tendency with contractors is to use any dirty sand or sandy loam available on the street. Such material, especially if it becomes filled with water, will yield under the blocks and will not support them properly. The sand bed should not vary materially in thickness. It should be laid and graded not more than fifty nor less than twenty feet in advance of the setting of the blocks.
56. Setting of the Blocks.—The blocks should be delivered in front of the block setters on the blocks already set. The blocks must be set in straight courses from curb to curb, the courses running at right angles to the street (except at street intersections). All the blocks in any one course must be of the same width. Each block should be so set that the whole of its bed will be seated upon sand. The usual practice of block setters is to make a bed by drawing the sand into a small ridge upon which the outer edge of the block is rested, its weight canting it against the course already laid. This usually leaves a cavity under the back edge of the block which neither the subsequent joint filling or ramming closes up, so that the block may rest permanently on only a part of its bed. The practice is so fixed with block setters that it will require firmness and persistency to prevent it, but you should insist that it be so modified as to give a solid bearing for each block over its whole base.
The blocks must be set solidly against each other so as to make the joints of the least possible width. Unless close attention is given to this the joints are likely to greatly exceed the width permitted by the specifications. Care should be taken that the blocks are set truly vertical so that their upper face shall be parallel to the plane of the street. In setting the blocks their straightest and truest face should be placed upward so as to make the surface of the pavement as smooth and even as possible. Block setters are often careless about this.
Ordinarily no grade stakes are set for the surface of the pavement and templates are seldom used, the block setters using only their eyes to make the surface conform to the intended contour of the street. This usually results in the completed street being more or less wavy and irregular, and in a lack of regular and uniform cross-section in different parts of the street, often very perceptible to the eye. Care should be taken to avoid this as much as possible. Straight-edges and templates, cut to the proper curve for the surface, should be provided and used.
57. Ramming the Blocks.—This part of the work is likely to be slighted unless carefully watched. The important thing is to have each block equally and sufficiently rammed to bring it to a firm bearing on the sand, as well as to bring its top to the proper grade. The rammers will be disposed to touch lightly blocks or areas which if thoroughly rammed would be driven below the true surface of the pavement, and subsequent travel may force these down, making depressions in the surface. It is a very common practice for the men working the rammers to shirk on this work by allowing the rammers to fall with little more force than that due to their own weight. This should be detected and remedied.
58. Filling the Joints.—The specifications are quite full and clear regarding this part of the work and little further need be said.
Care is necessary, whether the joints be filled with gravel and bituminous cement or with grout, to secure the complete filling of all the joints. If the weather is cold at the time the work is done, the gravel filling may become so chilled before the bituminous cement is poured that it will not flow to the bottom of the joints. For this reason it is important that the cement be worked at the highest temperature that it will bear without injury.
If grout filling is used care is necessary to make the mortar of the right consistency. If too thick it will not flow freely to the bottom of the joint; if too thin its strength will be materially reduced. Experiments should be made to determine the proper consistency, and when this is found, the quantity of water used in making the mortar should be determined and thereafter measured out for each batch.
The mortar must be kept constantly stirred until used, otherwise the sand is likely to settle to the bottom. Whatever filling is used, a second and sometimes a third pouring will be necessary to completely fill the joints.