98 



Bulletin 86 



continued for at least one minute more before the mixer is dumped. 

 The mortar on the floor must be used up quickly and no dry or set 

 mortar should be retempered and used. 



At Continental 607 cubic inches, or 22 pounds, of water were 

 used for a one sack batch. This is 23.4 percent of the weight of the 

 cement. The mortar when dumped was just wet enough to retain 

 its form when compressed in the hand. But when the outside jacket 

 was stripped from the fresh tile, the tile quaked like stiff jelly, and 

 small drops of water stood on the surface. When the mortar had 

 set, the surface was covered with a fine water-web ; this web may be 

 accepted as the test for correct consistency. The strength and im- 

 perviousness of the pipe depend in large part upon the percentage 

 of water used ; in every case it must be carefully watched, for the 

 amount of water needed varies with the brand of cement and with 

 the fineness of the sand. If the mortar is mixed too dry the pipe 

 may be pervious, and if too wet the strength is reduced. 



The unit quantities of sand and cement per tile, or per 100 feet, 

 is somewhat variable even on the same machine. The outside jack- 

 ets, when old, become stretched, and the packer-heads become worn ; 

 both of these causes tend to increase the thickness and weight of the 

 tile. The rate of feeding the elevator buckets and the speed of the 

 machine tend to vary the density of the tile walls. An approximate 

 estimate of the quantities required can be had from the following 

 data obtained at Continental. 



TABLE VL QUANTITIES OE MATERIAL FOR MCCRACKEN CEMENT PIPE 



The handling of the machine is an art and cannot be learned 

 from a bulletin. The normal method of learning to run a machine 

 is to serve an apprenticeship. The purchaser of a machine to be 

 used in Arizona should include in the contract that the manufac- 

 turers send an experienced pipe maker to install the machine and 

 to operate it for at least a month. 



The operator stands with the right hand on the clutch lever, 

 holding a large trowel in the left hand. With the trowel he can 

 hold back the mortar in the chute or can help it along. Too much 

 mortar chokes the packer-head and puts a heavy load on the engine. 



