3 ao THE IMPROVEMENT OF RIVERS. 



1 1 iatcly below the bottom lines of those surfaces, shall have a facing averaging ij 

 inches in thickness, composed of one part of cement and two parts of sand thoroughly 

 rammed in layers not over 4 inches deep, with a special rammer This rammer shall 

 be of bar iron, i inch square and 6 inches long, with a bent gas-pipe handle, and shall 

 have a total weight of about 8 pounds. The facing and backing shall go on simul- 

 taneously in the same horizontal layers. This work must Ix; carefully and thoroughly 

 done, and the contractor must provide competent laborers who shall be retained on 

 the facing work whenever it is being carried out. No careless or unskillful laborer will 

 be allowed to work upon it. If the mortar is mixed in the concrete mixi*r, the box 

 must first be thoroughly scraped free from particles of stone or gravel, and no stone or 

 gravel must show on a faced surface. As soon as the forms are removed, all such sur- 

 faces shall be examined, and all joint marks, lumps, or other disfigurements, shall be 

 carefully effaced. Facing which is broken or otherwise injured at any time before the 

 completion of the contract shall be cut out and satisfactorily replaced without cost 

 to the United States. 



Sand used for facing must be free from gravel, grit, or other material liable to show 

 on the finished work. 



40. Coping. The coping on top of the lock-walls and wing-walls shall be not less 

 than J inch thick, and composed of one part of cement to two parts of sand, well 

 bonded to the surface of the concrete below before the latter has attained its initial set. 

 The entire coping layer shall be divided, as shown on the drawings, by joints about 

 |" wide, and the edges of the walls shall be rounded as shown on the drawings. All 

 this work must be done by experienced sidewalk masons, and the contractor must 

 remove and replace at his own expense any of it that is not of the best class, and done 

 to the satisfaction of the Engineer. 







Sand used for coping must be coarse-grained, but free from gravel and foreign 

 substances. 



All coping and facing will be estimated as concrete. 



41. Protection, etc., of Concrete. Whenever concreting is suspended the surface 

 of the layer shall be at once completely covered by wet tarpaulins. These tarpaulins 

 shall not be removed for two days, unless work is recommenced on the block before 

 the two days have passed. Unfinished surfaces must be similarly protected from the 

 effects of sun and wind whenever so directed by the Engineer, to prevent drying out 

 before the mixture has set, and any concrete, facing, or coping, injured through lack of 

 protection shall be at once removed and replaced at the contractor's expense. 



All concrete shall be thoroughly drenched twice a day for three days after it has 

 been deposited. 



42. Frost. No concrete shall be placed in tenifx-rature lower than thirty degrees 

 Fahrenheit, nor when, in the opinion of the Engineer, it is liable to freeze before the 

 mass shall have set sufficiently to prevent injury; the contractor will be required to 

 protect at his own expense all work liable to be injured by the action of frost. In case 



