74 
CONCRETE SILOS 
Building Concrete Block Silos 
Hollow concrete block silos are popular in all of the northern states 
and more especially so in sections where the winters are extremely cold. 
The cost of concrete block silos is often a trifle more than for those of 
monolithic construction, although this is not true in a great many cases. 
The best concrete block silos are those erected by contractors who have 
made a specialty of this class of work. Good block silos can be put up with 
home-made blocks and by home labor, but where there is a reliable block 
contractor in the vicinity it generall}^ pays, in a saving of time as well as 
in numerous other ways, to have the work done by persons with previous 
experience. 
When the work is done by a contractor, the owner should take the 
precaution of examining the blocks which go into his silo, rejecting those 
p . . that are damaged or of an inferior quality. A crack of any size, 
Blocks or broken or crumbly edges, indicate a weakness in the block and 
make it unsuited for use. Blocks may be tested for their water- 
resisting qualities by placing a small amount of water on the surface and 
observing whether this remains or is absorbed. A block which readily 
absorbs moisture is obviously unsuited for silo work, which dampness 
must not penetrate. Warped and distorted blocks should be discarded 
because of their unsightly appearance. 
The foundation already described will give as good satisfaction for the 
block silo as for the monolithic (see pages 54 and 55). The top of the 
La in the ^^^^^^S must be made perfectly level, being tested frequently 
Blocks with a straight edge. As soon as the footing has sufficiently 
hardened, the top should then be cleaned off and moistened 
and a coat of slushy cement mortar 3^-inch thick put on. The first 
band of reinforcing should then be put in, and the first row of block laid 
on this mortar, beginning the blocks at the two ends of the wall next to 
the doorway and continuing around. The blocks may be more conveniently 
set in a true circle if a sweep similar to the one used in laying out the foun- 
dation is used here. Should the blocks fail to meet exactly, the circle should 
be enlarged or made a little smaller, whichever happens to be the more 
convenient. A guide board with a convex curved edge, cut on a circle of 
the same diameter as the inside of the silo, should then be made and used 
in place of, or in conjunction with, the sweep in laying up the remaining 
courses. 
The cement mortar should consist of one sack of Portland cement to 2 
cubic feet of clean sand, with the possible addition of a small quantity of 
The Mortar ^y^^^^t^d \\uie (not over 10 per cent) to make it easier to work. 
Before laying up the blocks see that they are thoroughly soaked 
which will prevent them from drawing moisture from the mortar. No more 
mortar should be mixed at one time than can be used up within 30 minutes 
after first moistening. 
Most failures reported on block silos have been due to a lack of 
sufficient reinforcing, caused in most cases by the overconfidence of the 
