Page:Cassells' Carpentry and Joinery.djvu/111

Rh was filled three parts full with inflammable material (no petroleum or grease, however), and a fierce fire maintained for more than two hours, after which it was extinguished, and the under side of the floor was found to be charred to a depth of ¾ in. In American factory and workshop buildings a layer of mortar is often introduced between two thicknesses of flooring, as shown in Fig. 389. Here 8-in. by 4-in. wooden joists support the flooring planks, which are 3 in. thick, on which a layer of mortar, ¾ in. thick, is spread. Floor-boards 1½ in. thick, laid on the top of this, form the working surface of the floor. Sometimes the floor-boards are laid in two thicknesses, crossing each other diagonally, as shown in Fig. 390, in which indicates the layer of mortar. The beams carrying the floors have air spaces round each end, and to avoid the danger of the wall being pulled down by a falling beam in case the latter should be burnt through, the upper end of the beam is cut away at both ends so that it can fall freely.

Fig. 388.—Solid Blocking carried on Fillets.

Solid wood-block floors are now much used in the basements of dwelling-houses, on the ground floors of public buildings, and for covering certain forms of fireproof constructions in the upper floors of warehouses, etc. The advantages they possess over the ordinary boarded floor are: damp-proofness, freedom from dry rot, greater lasting properties, and freedom from vibration, and they do not transmit sound nor harbour vermin; they are more sanitary, through the absence of shrinkage, and consequent open joints of the older system; and the absence of nails is also a great advantage, as the holes made by these are always unsightly, and when the boards wear down the heads project, to the discomfort of the users.

Fig. 389.

Fig. 390.

Figs. 389 and 390.—American Systems of Wooden Floors.

The Wood Blocks.—Wood blocks are generally made from 9 in. to 18 in. long by 3 in. wide, and from 1½ in. to 3 in. thick, of yellow deal, pitchpine, oak, birch, maple, or beech. They should be prepared from thoroughly seasoned and sound stuff. The firms who make a speciality of this work usually dry the blocks in hot-air chambers after working, and afterwards store them in a dry building. Precautions should therefore be taken, when receiving a consignment from the factory, to store them under cover until they are required; and it is wise not to order them until the place is ready, because their storage for any length of time in a damp building will defeat the object of the previous drying, and for this the purchaser has to pay. The smaller sized blocks are sometimes made with square joints, and are held in place by the cement or mastic with which the foundation is covered, but in superior work the blocks are also connected by grooves and tongues or dowels. Several patented systems are on the market, some of the best of which are here illustrated; these combine an interlocking of the blocks with the substance of the bed, by means of dovetailed grooves or inserted keys, and a connection with each other by means of pins or tongues.

Preparing Basement for Wood-Block Floor.—In preparing a basement to receive a