48 



jacket is now released and removed and the pipe left on the base ring until 1 

 it has hardened. For large size pipe to avoid lifting and carrying the pipe,, 

 the base rings are placed on the levelled ground instead of on the platform. 



Where the pipes have to be used for pressures slightly greater than 

 those given and especially for pipes above 18 inches in diameter, it is 

 advantageous to place in the moulds during the tamping process hoops of 

 ordinary wire about six inches apart. This permits using a slightly wetter 

 mixture and adds strength to the pipe without increasing the cost ma- 

 terially. 



Considerable practice is necessary before satisfactory pipe can be made- 

 and many pipes will be broken before sufficient experience has been 

 acquired. 

 Curing the pipe. 



When the process of moulding is completed the manufacturing is not 

 finished and the pipe may be ruined if not properly cured. The dry mix- 

 ture does not contain sufficient water for the cement to crystallize properly 

 and additional water must be supplied by sprinkling during the curing 

 period. The first sprinkling is done with a fine spray as soon as the pipe 

 has set sufficiently to stand it without washing. After this the pipe must 

 be kept continually moist by frequent sprinkling or by covering with wet 

 burlap or sacks for a period of at least one week and not be allowed to 

 dry or become white. 

 Coating the pipe. 



To make the pipe less pervious it is usually coated on the inside with a 

 thin paste of neat cement. Some prefer to use a cement lime mixture 

 made of 2-3 cement and 1-3 lime. The coating of the smaller sizes of 

 pipes, 6 to 12 inches in diameter, is often obtained by dipping the m"pe in 

 the liquid. For the larger sizes of pipes the coating is applied with a fiber 

 brush. It is preferable to do this as soon as the pipe will stand the hand- 

 ling, usually when it is 24 hours old, at which time the base rings can be 

 removed. To lift the larger size pipes a lifting jacket which fits around the 

 pipe and tightens when the pipe is lifted, is often used. 



Cost of moulds. 



There are various makes of moulds, some of which are very cheap. A 

 good mould must be substantially made to withstand the tamping and must 

 be easily and quickly set in position and removed. The largest manufac- 

 turer of the moulds used in southern California and supplied to the U. S. 

 Reclamation Service for use on some of its projects is the Kellar and 

 Thomason Company of Los Angeles, California. Their list price in Cali- 

 fornia of a set of moulds for 6 inch pipe with 100 base rings is about $50; 

 for 12 inch pipe with 100 base rings, $82.50; for 18 inch pipe with 50 base- 

 rings, $94.25; for 24 inch pipe with 25 base rings, $107.50; and other 

 sizes in proportion. 



Dimensions of cement pipes and rate of manufacturing. 



The table given below gives the thickness of the pipe, the number of feet 

 made per barrel of cement, the number of men in one crew of pipe makers, 

 and the number of feet of pipe made per day. The number of men stated 

 is the number required for a large production. The number of feet per day 

 is not the maximum which may be obtained but is an average rate for good 

 experienced men. The 1 to 3 mixture requires about 2 % barrels of cement 

 per cubic yard of concrete. For the 1 to 4 mixture 1 3 /i barrels of cement 

 per cubic yard are required. 



