LAYING THE BLOCKS - WOOD BLOCK The blocks are placed on end close together upon the plank foundation, and are packed in such a way that the spaces between the adjoining blocks have only three sides rather than four or more. The closest packing gives trian gular spaces. Projecting knots or bunches on the side of the block should be cut off, so that the blocks may stand close together. Occasionally it is necessary to split off a piece of a block in order to make it fit up closely against the adjoining ones; but no portion of a split block less than 3 inches in diameter should be used, and the edges of split blocks should be cut away so as to be not less than 1 inch thick at the thinnest part. Two split surfaces should not be laid in contact with each other. In paving against the curb, each alternate block should be split in halves, and the straight side be placed against the curb. In no case should blocks having the same diameter be set in a row across the street, but the various sizes should be intermingled with each other.
After the blocks are in place, the spaces between them are filled with pea gravel. Sometimes the gravel is simply swept into the joints, a surplus being left upon the surface to be worked in further by traffic; and sometimes the gravel is tamped into place; and in a comparatively few cases, tar or paving cement is poured upon the pebbles in the joints. If the gravel is tamped into place, there should be two men tamping for each one laying blocks. The tar makes the joints impervious and also assists in preventing the blocks from being displaced by traffic or from being floated away when the pavement is flooded. If paving cement is used, the blocks and the gravel should be perfectly dry. The hot tar in coming in contact with moisture forms steam which blows the tar full of bubbles and destroys its cementing power. The entire surface of the pavement is finally covered with about 1 inch of fine roofing gravel, which should be heated in order that it may bed itself into the tar.