FIRE-RESISTING P.UILDINGS. 8/ 



(/) By tlie remixing and use of old concrete after it 

 has set. 



((/) By excessive ramming or tamping or violent 

 trowelling of the surface. 



{h) By placing new concrete on old and dry work 

 without first saturating and preparing the latter. 



( ; ) B}- allowing the concrete to freeze or by deposit- 

 ing same in liot weather, which induces an initial 

 " set "' when mixing, which becomes broken in the 

 process of deposition. 



(7) The premature removal of " forms " or centres, or 

 the insufficiency or careless arrangement of same 

 or their supports. 



J'ailiircs due to lack of Scientific AppHcation. 



( k ) B}' errors in design or calculation. 

 ( / ) B}- the misj)lacement or omission of proper rein- 

 forcement. 



( ;/; ) By inefficient supervision coupled with careless or 

 incapable workmen. 



It must be patent to anyone, versed in the principles of 

 sound construction, that a concrete building is a monolith, and 

 as such is subject to extreme strains in case of a contiagration, 

 due to the expansion and subsequent contraction of its sub- 

 stance, or ])ortions of same, which is accentuated by the appli- 

 cation of cold water to its surface. 



This operation inflicts a comj)oun(l destructive factor in the 

 ];ossible disintegration of the protective covering of the rein- 

 forcement. The absolute necessity of laboratory tests and 

 analyses of materials is an established fact that no designer is 

 justified in overlooking when such structures are under con- 

 sideration. 



Cciliiujs. — Susj^ended or appended ceilings of incombustible 

 material are valuable factors in the protection of wooden floor 

 joists, and also of concrete floors. The types generally adopted 

 are those formed of metallic lathing with plaster applied, sheets 

 of compressed asbestos and cement, slag wool faced with 

 metallic sheets, and slabs of compressed pumice and cement, with 

 plaster applied. Alost of the foregoing types can be constructed 

 in double thickness, as w'itl'L an air space between them, Init in 

 the case of a new building, the cost would be more than that of 

 a concrete floor. 



The report of the British Fire Prevention Committee in 

 1899 proved that by covering both sides and the euds of wooden 

 floor joists with i" of slag wool, and by securing I94" of the 

 same material to the underside of joists with //s" boarding 

 below same, a fire of one hour's duration, with a maximum tem- 

 perature of 1,800° F. resulted in little or no damage to the 

 wooden joists or to the floor boards on the upper side of same. 



