When excavating for a concrete sidewalk, the ground shall be brought up to a subgrade of not less than six inches below the finished grade of the walk. The subgrade shall be thoroughly tamped if necessary to afford a solid foundation. A course of concrete not less than five inches deep shall be placed upon a two-inch sand cushion. The concrete shall be composed of workable Portland cement concrete having a compressive strength of 3,500 pounds per square inch. The concrete shall be tamped in suitable forms not less than five inches in depth. Expansion joints one-half inch in thickness shall be placed every twenty-five feet and where new work abuts existing sidewalks and curbs. A transverse contraction joint shall be made every twenty-five square feet of sidewalk. The Portland cement used in the sidewalk construction shall conform to the standard specifications of the American Society for Testing Materials, Serial D Designation C9-26, as amended and revised. Sidewalks shall have a wooden float finish true to line and grade and shall bear thereon the imprint of the name of the person constructing the same. All sidewalks shall be not less than five feet in width, except where permission is obtained from the Village Engineer.