LOCKS. 173 



other. The latter method, which was supposed to require that work on the block 

 must be continuous, has been modified in recent practice, and results equally good for 

 all practical purposes have been obtained by working in daytime only. With this 

 system the surface of the masonry is left in a ridge or a hollow along the center, and 

 carefully leveled at the edges and struck off with a trowel at the end of the day's work, 

 so there will be no ragged joints or wire edges. On resuming work next day the top 

 of the concrete is wetted, and cement scattered over it and brushed in, thus forming 

 a thin grout. The joints show very slightly in the finished work. If a joint of 

 appreciable thickness is employed, the mortar should not extend to the face, unless 

 it is made of facing material. By this means night-work can be avoided, an arrange- 

 ment which is always desirable, as it is very difficult to inspect concrete properly at 

 night, and in addition forms sometimes become displaced or rammed out of line with- 

 out being noticed. With monoliths it is also easier to secure uniformity of outline, since 

 the forms are set up at one time for the full height of the block. 



Each section of the wall should be bonded into the adjacent ones, not only for 

 stability but also because, the tendency to leakage through the joint is thus reduced. 

 In the first locks this bonding was made by placing vertically one, and sometimes 

 two timbers, about 8 inches wide and 4 inches thick, along each end of the section 

 being built. When the forms were removed the timbers were taken out, leaving 

 grooves into which the concrete of the next section bonded. We have observed, how- 

 ever, that any settlement of the walls always breaks off these tongues, and a better 

 method is to take V-shaped troughs, which may be made of i" X 12" lumber, and set 

 them on end, either close together or with a foot or more between, the end ones being 

 kept a foot or two from the face of the wall. These will provide a large number of 

 bonds without any weakening of the masonry, and will hold the sections together 

 against unequal lateral movement. 



Cost. The cost of a lock, including coffer-dam, excavation, construction of walls, 

 back-filling, valves, gates, and all labor and material needed to make it ready for opera- 

 tion, varies from ten dollars to fourteen dollars per cubic yard for masonry of cut stone, 

 and from nine dollars to twelve or thirteen dollars per cubic yard for masonry of con- 

 crete. These figures are obtained from examples of locks built within recent years, 

 the wide variation resulting from differences in cost of material, accessibility of site, and 

 other causes incident to all engineering works. 



