UNIVERSAL PORTLAND CEMENT CO. 
91 
Monolithic 
Roofs for 
Hollow 
Block Silos 
. gravel or crushed stone. The concrete should be mixed as wet 
Concreting without danger of running to the edges of the 
roof due to the pitch. The top should be trowelled off smooth, in the same 
manner as a sidewalk. Concreting should begin at the cornice working 
around the roof, so as to keep the concrete on all sides at an even height. 
As the work progresses toward the center a broad board, on which to stand, 
may be laid on the concrete already laid. It will also add greatly to the 
safety of the men working on the roof if a rope attached to the pinnacle 
is tied about the waist of each. In place of this, it is often desirable, for 
the sake of greater safety to the workmen, to put up a scaffolding on the 
outside of the silo. Special care must be taken to protect the roof from 
sun, strong wind and freezing until thoroughly hardened. For this pur- 
pose a covering of straw, manure, or canvas is generally effective; if either 
straw or manure is used it may be necessary to weight it down. The ef- 
fect of sun and wind is to dry the concrete out too rapidly, causing check- 
ing and cracking; while frost affects the strength of the concrete. 
Where it is desired to put a monolithic concrete roof on a hollow block 
silo, the wall should be laid up in the usual manner until the third course 
of block from the top is reached. The blocks used in this course 
should be solid, namely, made without cores, or if with the cores 
these should be filled up with mortar. The last two courses of 
hollow block should then be laid, the cores being left open. 
Special cornice blocks should be cast to make the cornice 
projection, and for this purpose a mold similar to that shown below 
can be conveniently used. The block should be 14 inches in width and 
of the same length on the inside of the 
wall as the wall blocks. The portion 
of the cornice blocks directly above 
the wall blocks should be 6 inches 
thick, while the projecting ends of the 
blocks should be but 5 inches thick, so 
as to give a one-inch drop. The roof 
framing is then put up in the same 
manner as described on page 88, but 
in this case it must be supported by 
the scaffolding instead of on the inner 
form mentioned there. The rein- 
forcing is placed in the same manner as described on page 89 and shown in 
illustration on page 90, excepting that the outer ends of the radial rods 
are made to extend down through the holes in the block for a distance of 
a foot or more. Since the holes in the third course of block from the top 
were either omitted or filled up before these blocks were laid, holes in the 
two upper courses can be filled up with wet concrete as soon as the rein- 
forcing rods are in position. The roof is concreted as described above. 
Before the concrete is placed on the cornice blocks this must be moistened 
and then painted with a cement and water grout. 
Cornice block for concrete block silo. 
