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 Rh be fixed nearer to the lower edge of the board than to the upper, so that as much wear as possible can be had out of the floor before the tongue is exposed. Another method of attaining the same object is known as rebating and filleting (see Fig. 378); a rebate is cut on the lower edge of each board, and a fillet of oak or some other hard wood fixed in the space thus formed. For superior work, a dowelled floor (Fig. 381) has the advantage of showing no nails on the surface; the boards are pinned together between the joists with oak dowels, and nailed obliquely on one edge only. Dowelled boards should not be more than 3 in. wide, and not less than 1¼ in. thick when finished. The "Pavodilos" joint is as shown by Fig. 382, a slightly modified form being that shown by Fig. 383, which, although the second key is lost, may possibly be preferred on account of the danger, when nailing down the flooring jointed as in Fig. 382, of damaging the feather-edge of the board that is being fixed.

An upper layer of thin oak boards is sometimes fixed over a rough deal floor for the sake of appearance, and also in some cases to obtain an almost impervious surface. A floor of this kind, wax-polished and well laid, is much to be commended for the ease with which it can be cleaned, and for its non-absorbent nature.

Fig. 382.

Fig. 383.

Figs. 382 and 383.—"Pavodilos" Joint in Flooring.

One method of preventing the sound from one room being audible in another room immediately below is to nail fillets to the joists, and on these nail a layer of rough boards, and to fill in on the top of these boards a stratum of lime-and-hair mortar. Slag felt, a preparation of slag wool, which is a material produced by blowing off waste steam into the slag of iron furnaces, is also used for this purpose. In the case of the slag felt the process is as follows: On the under side of the joists, fillets are nailed to wooden blocks 1 in. thick, and to these fillets the lathing for the plaster ceiling is affixed. The slag wool (known as "pugging") is then laid on the upper surface of the laths, and is felted by a patent process, this process of felting removing entirely the property which the slag wool possesses of emitting sulphuretted hydrogen, and also reducing the weight of the material. Slag material, being fireproof, is to be preferred to sawdust and other combustible materials sometimes used. Fig. 384 shows the section of part of a common floor, showing 9-in. by 3-in. joists, and 1½-in. boarding with a rebated heading joint. In addition, "pugging" and a lath-and-plaster ceiling are shown. The object of the pugging is to reduce the transmission of sound. The fillets for supporting the pugging need not be of the shape indicated in Fig. 384. Another means of attaining the desired end is to nail strips of felt on the upper edges of the joists, under the floor-boards. By this means the connection between the joists and boarding is broken. This arrangement creates some difficulty in fixing the boards, which can be overcome by nailing a lath along the top of the felt.

Fig. 384.—Section of Sound-proof Floor with Pugging.

Protected Wooden Floors.—One of the simplest and most economical methods of constructing a fire-resisting floor is to protect an ordinary wooden floor with slabs of asbestic plaster or of slag wool (silicate