"Forms on finished work should not be removed in less time than from 3 to 14 days, depending on the setting of the cement, the condition of the weather, and the height of a day's work. Forms on unfinished work should not be removed in less than from 12 to 72 hours, depending on the foregoing.
"On each new part of the finished work, the forms should be removed as soon as practicable, so that it may be assured that the method of placing the facing is a good one; if not, there will be a chance to improve upon similar sections of work.
"All layers of concrete should be horizontal, except near the skewbacks of heavy arches, where they should be inclined as nearly to right angles to the thrust of the arch as may be consistent with a compact concrete. A drier concrete than is generally used in mass work may properly be used here. The contractor should be required to set wooden blocks from 6 in. x 6 in. x 2 ft. to 8 in. x 8 in. x 4 ft. in the concrete, taking up approxi mately 10 per cent of the area in the finish of each day's work. These doweling blocks should be removed the following day. This is done for bonding purposes, and great care should be taken to see that this rule is carried out at all abutting sections of transverse arch blocks.
"All mortar for face work should be made by hand or a regular mortar mixer.
"The contractor must not continually change the facing hands who are skilled in this class of work. The uniformity of the appearance of concrete work is desirable, and is dependent largely upon this class of labor.
"Transverse and longitudinal arch blocks must be cast continuously, and the contractor must not start such work unless provided with sufficient plant and material to insure the finish of such a section continuously.
"The concrete should be of such consistency in gen eral that a man in walking about in it will sink ankle deep. This may be somewhat cut down in cold weather.
"Note the color of the concrete; and if it varies considerably, examine for cement. Find out whether the variation is due to the color of the sand or stone or variation in the cement. Occasionally a batch may get into the work with little or no cement in it, if the color is not kept in mind.
"Keep your work always neat as to the grade of the concrete. If the work is not handled systematically, you
cannot get first-class work, nor will it be economical to the contractor.
"Keep your face work always high, so that any of the concrete water which may accumulate will not go to the face work, for if it does it will weaken your face work and carry to it a lot of slime or laitance; silty sand is not good for face work.
"If your concrete is too wet, don't bail out the water, as it is full of cement. (In trench work bailing may be necessary.) Dry it up with a relatively dry concrete. Do not permit the hoisting engineers to continually strike the forming with the concrete bucket. Do not permit direct attachments of machinery to the forms, as it will result in vibrations which may be detrimental to your face work.
"Use soupy concrete when placed in water; and in muddy water, try to carry the concrete work on con tinuously; otherwise you will have layers of laitance and mud from to 1 in. or more in thickness, which are weak and will result in the settlement of your completed structure.
"In one case on my work the top of concrete which was used for sealing the bottom of a cofferdam, and which had been left for about ten days before the coffer dam was pumped out, was found to contain a great deal of this class of rotten material. The bottom of the cofferdam or the top of the seal was very rough; and in the valleys, which varied from 2 to 3 ft. in depth, I found as much as 8 in. of this useless material.
"Don't shovel concrete into water. Place it in as large batches as practicable, and lower with bucket or pipe.
"Don't dump large quantities of concrete into narrow forms. You will not be able to get sound facing work if you do.
"General Points on Concreting. Clean all loose silt, dirt, and grease from iron. Use wire brushes and putty-knives.
"Use soupy concrete for concrete-steel work.
"Use rammers having special shapes where neces sary. Bevel rammers are necessary for the backs of arches. Railroad tampers for heavy steel reinforcements. Short-handled rammcrs in confined places, and long handled rammers in columns. Fine stone forks are better than spades on plain face work where the concrete stones are as large as 2 in.