1869.] Roofing. 543 HOOFING. HAYING already discussed slate as a material for roofing, we now briefly advert to other of the more immediately useful and practical sub- stances, or applications of substance, for that purpose. And, first : — • GRAVEL ROOFING. For this kind of roof, if a good job is desired, it is a matter of prime necessity, to have the wooden sheathing, which forms the basis of the room, well se- cured to the rafters, and laid perfectly smooth. The slant must also be true and uniform ; and all the knot holes must be carefully plugged up and smoothed over, as all such apertures are apt to cause breaks beneath the feet of any one passing over the roof, and consequently leaks. The felt, which really forms the preventive against leak- ing, and is actually a kind of woollen paper, is now loosely laid upon the boards of the roof, to the extent of three thicknesses, breaking joints with each other, and is properly secured by cleats. This done, the felt is completely cov- ered with coal gas tar, of a consistency that will not run in warm weather. This consistency can only be determined by the experience of a practical and practised roofer, in these materials. The tar is very evenly spread or smear- ed over the felt, by means ©f a cotton mop. The mopping, also, is a part of the general operation, which can only be adequately performed by an experienced workman. We are informed by Messrs. Warren, Kirk, & Co., Farqnhar Build- ings, No. 228 Walnut street, who have very obligingly afforded us all the in- formation in their power — whose expe- rience in the matter is not slight, they having used 6,000 tons of gravel upon 2,000,000 square feet of roof last year— that out of a hundred men in their em- ployment, only fifteen are competent to mop a roof. The quantity of tar also must rest upon the experienced discre- tion of the mopper. Too much will run, to the great disfigurement of the house front, and the intense disgust of the passers by. While the above is going on, the la- borers are heating small pebbles, in a large cylindrical iron pot, by means of a wood fire in the open street, before the premises, and these are hauled up in a little keg, with a rope and simple pulley, attached to a light temporary derrick, and equally spread over the soft tar. The heating is to the end, that the gravel stones may sink in, and more firmly attach themselves to the surface of the tar. The superfluous pebbles, or gravel stones, are now lightly raked off, and saved for another occasion, and, all the drains, gutters, &c, having been previously arranged in the wood-work and the felting, the roof is now com- plete. The object of using the pebbles, is to protect from the weather, the surface of the tar, and this, in turn, protects the surface of that more important covering, the felt. The best pebbling is ocean gravel. That used in the vicinity of Philadel- phia, by the firm lately mentioned, being from Horton's Point, Long Island, New York. These roofs are made of many differ- ent inclinations to the horizon ; but should, of course, be rather flat than steep. From one-half to three-quarters of an inch to the foot is absolutely ne- cessary ; and a roof of six inches to the foot is, by the roofers, warranted to be of the very best. Note. — Want of space has compelled the omission of a portion of this article, comprising another kind of Roofing: to follow in our next.
