THIRTY-SIXTH ANNUAL CONVENTION. 311 



Durability. 



The walls of the Iowa silo are constructed of hollow, vitri- 

 fied clay building blocks, which as far as weather resistance is 

 concerned, are as durable as any building material which can be 

 obtained. Their durability corresponds with the durability of 

 brick which is to be found in all parts of the State. This does 

 not mean that all hollow building blocks are durable, for there 

 are good and bad blocks on the market. Good blocks are so 

 plentiful that no one need make the mistake of selecting blocks 

 of questionable merit. A discussion of the quality of blocks is 

 given later. 



The roof of the Iowa silo, like the walls, is made of durable 

 material. A cheaper roof may be used if desired, but it is 

 strongly advised that the concrete roof be used where possible. 



One common mistake met with in silo construction is that the 

 door frame is made of material which will soon decay or rust 

 and have to be replaced. The door frame of the Iowa silo is 

 made of reinforced concrete which, when properly constructed, 

 should be as durable as the walls themselves. 



The materials used in the Iowa silo will resist decay, dis- 

 integration, the action of frost, and any implied or real action 

 of the acidity of the silage. Even the steel which is placed in 

 the mortar joints and concrete door frame as reinforcement, is 

 thoroughly protected from rust. So carefully has the matter 

 of durability been considered in the design of the Iowa silo that 

 it would be difficult to estimate its Hfe. When carefully built it 

 ought to last for several generations. 



The doors of the Iowa silo are designed to be made of wood. 

 They will decay and must be replaced after several years. The 

 convenience and low cost of the wooden doors, which may be 

 easily replaced, justifies their use. 



Care and Repair. 



The Iowa silo when properly constructed is practically free 

 from any expense for repair and maintenance. The only pos- 



