120 THE SAN FRANCISCO EARTHQUAKE AND FIRE. 
skew backs, not less than 1J inches thick, or be covered with at least 
2 inches of concrete. In an important work the protection of the 
lower flanges of the floor beams should also be incased in expanded 
metal or wire lath. The furred ceilings so much used in San Fran- 
cisco are a valuable addition to the fire-resisting qualities of floor 
construction, and if the furring rods were more firmly secured the 
total loss here, as a rule, would be measured by the value of the 
plaster alone. 
Hollow-tile partitions should not be less than 6 inches thick. The 
tiles should have webs at least 1 inch thick, and all interior angles 
should be well filleted. The tiles themselves should be carefully laid 
in Portland-cement mortar, with all joints absolutely filled. Timber 
studs running to the top of the partition, to frame a door or window 
opening, should be absolutely prohibited. The webs of floor tiles 
should not be less than an inch thick, and their interior angles also 
should be well filleted. 
The results at Baltimore and San Francisco did not, by any means, 
indicate that either hollow tile or concrete is altogether a failure or 
altogether a success. Both fires indicated very clearly that com- 
mercial methods of applying both materials are inadequate, but also 
that successful results can be attained with both materials. 
A conflagration never yields reliable comparative results, but 
judging from such comparative results as are available, I think that 
there is no question that the best fire-resisting material available at 
the present time is the right kind of burned clay — that is, a good, 
tough, refractory clay, almost as refractory as fire clay, made into 
proper shapes and properly burned. Some commercial hollow-tile 
Avork is made of good material, but, as a rule, that is the only good 
thing that can be said about it. There can be no question that good 
clinker concrete, made of well-burned clinker, Portland cement, and 
sand, is a very efficient fire-resisting material. It is better than any- 
thing except the better types of burned-clay products ; but the cinder 
concrete commercially applied is, on the whole, no better than the 
flimsy hollow-tile work with which it competes ; in fact, it is not cer- 
tain that it may not be worse. The only way to determine this point 
would be to go through all the floor construction in a place like San 
Francisco and make tests of the load-carrying capacity, etc., after a 
fire. It is very doubtful, of course, whether such tests will be made. 
If a hollow-tile floor, for instance, loses its lower webs, the damage 
is very apparent, yet most of such floors remain true and capable of 
carrying considerable loads. A cinder-concrete floor which is even 
more seriously damaged is very likely to remain true, for the reason 
that the fire which damaged it also removed its superimposed load 
before the damage was fully accomplished. xV hollow tile which 
comes through a fire without losing any of its webs is as good as it 
