CONSTRUCTIOlSr AND FIKE PROTECTION OF COTTON WAREHOUSES. 37 



materials which frequently can be used to better advantage and are 

 more easily kept in place while the concrete is being deposited. 

 Punched sheet steel also may be used provided the metal is not too 

 thin/ 



Forms for reinforced concrete may be used with maximum economy 

 in construction of the warehouse. The uniformity of requirements 

 with the consequent duplication of units, or compartments, makes 

 possible a very high degi-ee of standardization in form work with 

 the result that forms can be used over and over again. The usual 

 construction is with forms built of wood, though forms of steel are 

 coming into use. Steel forms for columns, particularly those with 

 flaring heads used for flat-slab construction, are desirable. Steel 

 forms are also in use for wall construction. For floor or roof slab and 

 beams, wooden forms generally are used and fulfill every require- 

 ment. These should be constructed in units of such size as to permit 

 easy movement for additional use. The slab forms should be made 

 of ordinary matched fl.ooring; the same material may be used for 

 beams and columns, though for this use material 1^ or 2 inches thick 

 and closely jointed is to be preferred. It is of primary importance 

 that all form construction be very rigid and of sufficient strength to 

 support the heavy wet concrete without distortion, as any disturb- 

 ance of concrete during setting is a serious impairm.ent to its 

 strength. 



The floor slab should be finished with 1 inch of top dressing 

 mortar composed of the same material described for finishing the 

 paved floor. In this case the hydrated lime may be omitted, if de- 

 sired. The rough slab should be wet thoroughly before this mortar 

 is applied to insure a good bond between the two. Only the rough 

 slab thickness should be considered in calculating the strength of the 

 floor or roof.^ ^ 



*. Reinforcement should not be painted, as this renders less efEective the 

 bond or " grip " of the surrounding concrete upon it. This objection also 

 holds good in regai-d to excessively rusty metal. Particular caution should be 

 exercised against the use of badly rusted wire or punched steel, as here the 

 amount of surface, as compared with the sectional area is large, and hence a 

 definite penetration of rust gives: a correspondingly greater reduction of 

 strength than would be true of the larger rods. 



Mixing of concrete should be done very thoroughly, the best results being 

 obtained by the use of a machine of the type known as the " batch mixer." 

 Sand and cement should be mixed dry before the water is added. Mixing 

 should not be done in freezing weather. The concrete should be placed as fast 

 as it is mixed, and should be tamped thoroughly to secure a dense mass free 

 from voids. Reinforcement should be placed and inspected in advance and 

 should be well secured against displacement. 



" The roof slab should be smoothed of£ carefully as casting is done, or else 

 there should be added a top dressing of 1 part Portland cement to 4 or 5 



