CONSTRUCTION AND FIRE 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. 1 
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 degree 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 flooring; the same material may be used for 
beams and columns, though for this use material H 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 impairment 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. 2 
1 Reinforcement should not be painted, as this renders less effective the 
bond or " grip " of the surrounding concrete upon it. This objection also 
holds good in regard 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. 
2 The roof slab should be smoothed off carefully as casting is clone, or else 
there should be added a top dressing of 1 part Portland cement to 4 or 5 
