14 BULLETIN 906, U. S. DEPARTMENT OF AGRICULTURE. 
The bottom of the trench should be laid as nearly as possible to 
grade, but the grade does not need to be uniform where the pipe is 
under pressure, although sudden changes in grade should be avoided, 
as such irregularities in the pipe line may collect air, which will 
decrease the carrying capacity of the pipe. If it is not possible to 
avoid alternate dips and rises, air vents should be provided for at the 
highest points in the line. Where the line makes a deep dip, a blow- 
off valve should be installed at the lowest point, so that any accu- 
mulation of sand or trash can be blown out. 
Most experienced pipe layers lay small sizes of pipe by standing 
the joint to be laid on end and filling the groove end with mortar. 
The pipe is then firmly pressed against the tongue end of the pipe 
that is already laid in the ground, care being taken to get a good bond 
of mortar between the ends of the pipe. The mortar is smoothed off 
with a trowel on the outside, and the inside brushed smooth with a 
long-handled brush. The ends of the pipe are always wetted with 
a brush before applying the mortar. 
Large-diameter pipe is usually laid by placing a batch of mortar 
in the bottom of the groove of the pipe that is laid and on top of the 
tongue end of the pipe to be laid. The tongue and groove of the two 
joints of pipe, respectively, are then pressed together and the joints 
filled in by hand, using a rubber glove or part of an automobile 
inner tube over the hand to protect it from the action of the cement. 
The inside of pipe of a diameter less than 22 inches is finished off 
by a long-handled brush, but larger pipe is finished or pointed off 
b} T a man who works inside of the pipe. If it is possible for a man 
to work inside the pipe it is best to finish the inside of the joints 
24 hours or longer after the pipe has been laid. This gives the pipe 
time to settle, otherwise joints may crack if finished off at once. The 
pipe also has time to expand or contract before the inside is finished. 
For this reason most contractors would rather guarantee pipe against 
leaks when it is large enough to permit a man to work within it. 
Pressure pipe and the larger sizes of ordinary pipe are usually 
finished with banded joints, but small pipe that is to be under low 
pressure is not banded as a rule. The band is formed around the 
joint on the outside of the pipe with a trowel. The average size 
of band is about one-half to three-fourths inch thick over the joint 
and 4 to 6 inches wide. Some pipe layers reinforce the joint of high 
pressure with wire mesh. The wire is tied around the joint and the 
band made by plastering the mortar over it. 
Laying cores are made use of occasionally in assisting to make 
joints. The core fits inside the pipe and prevents mortar from being 
projected into it. 
Mortar used in laying is usually made of one part of cement ro 
one and one-half parts of fine sand. The mortar is often made by 
