For placing the side-walls, a special traveling form was used, the details of which are shown clearly on Plate XIV. At the end of each form an expansion joint of 25 cm. was left to be filled after the roof was placed in position. The concrete was delivered to the wall through stove-pipe chutes, and carefully spaded by workmen in the limited space between the forms and the embankment. The wall form was removed after 36 hours, by loosening the jacks and pulling forward the hooked tie-rods. This form is also shown on Fig. 2, Plate XVI.
[Illustration: PLATE XVI, FIG. 2.--TRAVELING SIDE-WALL FORM, OBISPADO RESERVOIR.]
[Illustration: PLATE XVI, FIG. 1.--PREPARING FLOOR FOR CONCRETING, OBISPADO RESERVOIR.]
The concreting of the roof slab was carried on continuously, and, when partly completed, the floor was laid in the shade. The bottom layer of the floor, 13 cm. thick, was laid in continuous panels between the columns, and brought to a fairly smooth surface. On this surface, after keeping it wet for 10 days and then allowing it to dry thoroughly, a layer of asphaltum, supplied by the American Asphaltum and Rubber Company, of Chicago, was placed. The work was done by ordinary Mexican laborers after they had received a few days' instruction from one of the Asphaltum Company's superintendents. The surface of the lower layer was kept perfectly clean, and then received one coat of "Pioneer" paint. The asphaltum, heated in a boiler inside the reservoir to a temperature of approximately 425° Fahr., was then poured over the floor from buckets, in a layer approximately 4 mm. thick. Where the floor joined the column pedestals, and at each new panel section, a double thickness was used. The labor cost of water-proofing, including superintendence, etc., amounted to 3.3 cents (Mexican) per sq. m. for painting with "Pioneer" paint, and 5.4 cents for the asphaltum coating, or a total labor cost of 8.7 cents per sq. m. for the complete water-proofing. This cost is based on a rate of 8.00 pesos per day for a foreman, and 1.00 peso for each laborer. It required 50 U. S. gal. of the paint to cover 265.2 sq. m., and an average of about 6 lb. of asphaltum for 1 sq. m.
The upper concrete layer of the floor, 10 cm. thick, was placed so as to break joint with the lower, and was brought to a smooth surface with wooden floats sheathed with steel and reaching across the panels. In this way a perfectly smooth surface was obtained without any plastering.
