Timber should be kept out of walls as much as possible. The evils produced by building in large pieces of timber will be pointed out in Part II. It is, however, frequently necessary to introduce pieces of wood in walling for different purposes, in which case they should be as small as practicable.
When the ends of timbers, such as girders, joints, tie-beams, etc., have necessarily to be built into walls, they should rest in chambers prepared for them, so that there may be a free circulation of air round the timber.
Wall Plates1 are described at p. 129. They are sometimes built into the wall, but are there liable to the same objection, in a lesser degree, as bond timbers (see Part II.)
Wood Lintels are beams over openings, such as those for doors or windows, shown in Figs. 99, 549, etc.; they should never be used without a relieving arch as shown in those figures (see p. 32), and they may be replaced by flat arches, as in Pigs. 525, 545, etc., or by cement concrete beams made with ashes or breeze from gasworks, so as to admit of the woodwork being nailed to them. (See Pig. 545.)
The arches and concrete have an advantage over wood lintels, inasmuch as they are not liable to destruction by fire or decay.
Thickness of lintel in inches should be equal to span in feet; that is, thickness of lintel = 1/12 span, or some take it = 1/8 span. The ends of the lintel should, as a rule, bear 9 inches on the walls, but 4 1/2 inches' bearing is often considered sufficient.
Bressummers are beams, either of wood or iron, spanning wide openings, and generally supporting a wall above.
Wood Bricks2 are pieces of timber built into brick walls, in order that the necessary woodwork of the building may be secured to them.
They should be of the shape of the bricks in use, and equal in thickness to one of those bricks and two mortar joints, so that the rough surfaces of the adjacent bricks may have a firm grip on the wood. If wood bricks are imbedded in mortar they are nearly sure to become loose.
1 Ir. Tassels. 2 Sc. Dooks.
Pallets or Wood Slips are flat pieces of wood, about 9 inches long, 3 inches wide, and 3/8 inch thick. They are built into the joints of brickwork or masonry, to fulfil the same object as wood bricks, and have to a great extent superseded them, as they shrink less, and do not leave such a gap in the wall if they decay or are burnt out.
Wood Plugs are used in masonry, and sometimes in brickwork, for the same purpose as wood bricks. When anything is to be nailed to a wall, a plug should be driven in first, as the nail will not hold in the masonry.
Plugs should be about 4 to 6 inches long, 1 1/2 or 2 inches wide, and about 1/2 inch thick, and in order to give them a better hold on the masonry they are cut with a twist, so that the grain of the wood runs obliquely across their thickness, and their sides are not parallel but splayed and in winding.
Great injury is often done to walls by driving wood plugs into the joints, as they are apt to shake the work, especially if it lias been recently built. It is better to cut holes for the plugs in the solid stone or bricks.
Examples of plugging are given in Fig. 544, and others.
To avoid driving pings into masonry, tubular bricks are sometimes built in the required positions, with plugs driven into the hollow spaces in their interiors. Pallete Bricks, which have a rebate of dovetail-shape section formed along the upper outer edge to hold a fillet, are also used.
If it is desired to dispense altogether with wood in the walling, small double strips of hoop iron may be placed in the joints at every point where a nail is to be driven. These firmly grip the nail, which is driven in between them. Strips of lead may be used for the same purpose.