46 
The Colorado Experiment Station. 
best tools for both wet and dry mixing. Care should be taken not 
to permit the water to run off and carry cement with it while mix¬ 
ing. When made wet enough the entire mass can be shaken by 
patting it in the center with the shovel. It will be wet enough to 
deliver from the bucket into the forms nicely. 
Elevating .—An extra pulley attached to one of the quarter 
arms of the scaffolding is used in elevating the concrete. One man 
stands upon the ground and pulls this up. No saving in time or men 
can be effected by the use of a horse in hoisting cement. The one 
man draws it up as rapidly as it can be handled above. 
Tamping .—Thorough tamping of the cement in the silo forms 
is a very important matter. The man who fills the forms should 
work gradually around the silo, filling to a depth of about six inches 
as he goes. He should be followed closely by the man who does the 
tamping. 
Tamper .—A desirable tool for a tamper is made by straight¬ 
ening the shank of a hoe until the blade is straight with the handle. 
With this sharp edge the concrete can be thoroughly tamped. It is 
desirable to run the hoe blade between the outside form and the re¬ 
inforcing. Although the reinforcing is against the outside form, 
it will be covered with concrete if this precaution is taken. Very 
careful tamping should be done around the door jambs. When the 
concrete is properly tamped it will be smooth and soft on top and 
if the proper amount of water has been added, the concrete will 
jiggle as the tamping is done. A little water will soon raise to the 
surface of the concrete. If this collects in excess and runs out of 
the forms too much water has been used in mixing. When water 
runs out of the forms in this manner it washes the cement off the 
rocks and sand and weakens the wall. 
Wetting the Surface .—Each day before the first concrete is 
placed in the forms, water should be thrown upon the surface of the 
wall completed the day before, and a few handfulls of dry cement 
should be sprinkled over the moistened surface. This will result in 
a more perfect union between the different courses. 
Tarring the Silo .—The inside surface of the silo wall should be 
rendered air and water tight by the application of a coat of No. 7 
soft tar pitch. 
The pitch should be melted in kettles until it is thin enough to 
be applied smoothly and readily. When only partially melted, an 
excessive quantity will be used. The pitch may be applied with 
swabs. The swabs are made by attaching rags or mop material se¬ 
curely on the end of a handle, such as a broomstick handle. The 
swab will have the appearance of an ordinary mop except that the 
