THE PIREPROOFING OF CITY BUILDINGS. 577 



3. To make u\) for the use of the inflammable timber the joists 

 may be pugge 1 with hair mortar, (PI. XXXIX., tig. 1). When 

 the plastering gives way the ]mgging prevents the flames getting 

 round all three sides of the joists. 



4. Instead of using plastering or pugging, the ceiling may be 

 formed of sheets of galvanised iron, kept three inches away fron\ 

 the joists and coated on the top with two inches of hair mortar, 

 (PI. XXXIX., fig. 2), as at the Courier building in Brisbane. 



5. A still better mode is to line the ceilings with light porous 

 terra-cotta tiles, hung up to the joists by iron screws and clips, or 

 hoop or angle iron, but kept one inch away from the wood, (PI. 

 XXXIX., fig. 3). They may be left bare or plastered. This 

 system is a good one, but adds somewhat to the weight of the 

 floor. It is used in the United States. 



6. Instead of ordinary deep joists at eighteen inches centres, 

 timbers almost square, set at three to six feet centres may be used. 

 These are covered with three inch planking, with grooved and 

 tongued joints. (PI. XXXIX., fig. 4.) This models occasionally 

 adopted for warehouses, both in England and the States, but is 

 common in bridge work. It is quite slow burning in comparison 

 with a floor composed of the ordinary joists and boards. If the 

 undei-side be limewashed, plastered, or cased with galvanised iron 

 ortin plates, its resistance is materially increase I. 



7. Ordinary deep joists may be set close together and spiked, 

 screwed, or bolted to one another. (PI. XXXIX., fig. 5.) The 

 joints are filled with fine plaster or cement. The ceiling may be 

 coated with plaster (large flat-headed nails forming the key), and 

 the floor with cement or tiles. It is well to lay an inch of loam 

 under the cement or tiles to prevent cracking. This system is known 

 as Evans and Swain's,* and is useful when timber is cheap and the 

 risk of failure from dry rot and white ants is not great. 



8. Timber po.«ts and beams of large size have been found more 

 fire-resisting than unprotected cast iron columns and rolled iron 

 girders. The timber chars to the depth of an inch or so and will 

 then stand for a considerable time. This was especially noticeable at 

 the Evening Neios office tire. A coat of limewash, fireproof paint 

 or solution, or a lining of galvanised iron or tin is very desirable 

 where the risk is considerable, as for instance, where there is much 

 oil in use, which would soak into the wood. Oily cotton waste 

 in conjunction with an oily floor is especially dangerous, being 

 vex'y liable to spontaneous combustion. A coat of hair mortar 

 mixed with chloride of lime, with large headed nails for a key, 

 also stands well when not suV)ject to hard weai-, and is still more 

 fire resisting than the protecting coatings just mentioned. Un- 

 protected cast iron columns melt if the heat is fierce, or crack, if 

 the hose is turned on them while red hot, and rolled iron joists or 



*See Appendix A. 

 L 1 



