5-18. COMPACTION: Concrete, except when placed and com- pacted By pneumatic means, by pumping or other specified method, shall be placed in layers not over 12 inches deep and each layer shall be compacted with the aid of mechanical internal-vibrating equipment supplemented by handspading, rodding and tamping as directed by the Engineer, Vibrators shall in no case be used to transport concrete inside the forms. The use of form vibrators will nat be permitted, Internal vibrators shall maintain a speed of not less than 5,000 impulses per minute when submerged in the concrete. At least one spare vibrator shall be maintained as a relief, The duration of vibration shall be limited to that necessary to produce satisfactory consolidation without causing objectionable segregation, The vibrator shall not be inserted into lower courses that have begin to set. Vibrators shall be applied at uniformly spaced points not farther apart than the visible effectiveness of the machine, 5-19. BONDING AND GROUTING: Before depositing new concrete on or against concrete which has set, the existing surfaces shall be thoroughly roughened and cleaned of all laitance, foreign matter and loose particles. Forms shall be retightened and the existing surfaces slushed with a grout coat of neat cement. The new concrete shall be placed before the grout has attained its initial set. Grout for horizontal construction joints shall be of cement and fine aggregate in the same proportion as the concrete to ve placed, and shall be from 1/2 to 1 inch thickness. Grout for setting column bases, wall plates, and other metal items, shall be composed of equal parts of sand and cement, with water sufficient to produce the required consistency. 5-20, FINISHES oF CONCRETE OTHER THAN FLOORS AND SLABS: All concrete sha ve any sligh oneyco and minor defects patched, using cement mortar composed of 1 part of cement and 2 parts of fine aggregate. Exposed surfaces shall be given one of the following finishes, as indicated on the drawing or specified: Be RoughFinish: Concrete for which no other fin- ish is indicated or specified shall have 411 fins and rough edges removed. Undressed boards may be used for the forms where this finish is to occur, bd. Smooth Finish: Smooth finish shall be given to all exposed concrete surfaces unless otherwise indicated Smooth finish shall be obtained by use on the drawings. of ptywood forms or form linings. Sheets shallbe as large as practicable, with smooth, even edges and shall be 2713