Concrete Silos 115 



Sometime during the process of applying the 

 scratch coat, the space under the door should have been 

 cased up inside and out and filled with mortar mixed 

 in the proportion of 1 part of cement to 2 l /2 parts of 

 sand. A strip of wood should be placed across the bot- 

 tom so that the shoulder which is cast at the side of 

 the doors will be continued across the bottom of the 

 door. 



When the scratch coat is all on, the door posts are 

 to be filled. Since the 8-inch boards forming the in- 

 side of the form have a tendency to spring back under 

 the weight of the mortar, some provision must be made 

 to hold these boards rigidly in place. This can easily 

 be accomplished by firmly nailing short braces to the 

 scaffold plank at each platform, the ends being braced 

 solidly against the back of the form. 



If this work can be completed by quitting time at 

 night, or even by working overtime, the thin boards 

 on the inside can be removed the next morning. Con- 

 siderable care must be used in removing these boards, 

 since the mortar will be rather green and easily in- 

 jured. The placing of the remaining layers of plaster 

 can now proceed with no further delay. 



The mixture for the second layer of plaster should 

 consist of 1 part of cement to 2% parts of sand, and 

 should be applied in three coats, giving a total thick- 

 ness, including the scratch-coat of at least 1% inches. 

 In applying these coats, begin at the top and work 

 down, one coat following the other as rapidly as pos- 

 sible. An old broom should be kept on the scaffold, 

 and the helper should rough up each coat as soon as it 

 has wet sufficiently, so that succeeding coats will not 

 be applied to the glossy surface left by the trowel. It 



