Regular work the best.

The use of " bond-stones " at intervals only is bad; they should be carried through the whole surface (width and length) of wall and be of even thickness, or else be omitted. Using bond-stones in one place only tends to concentrate the compression on one part of the wall Thus, bond-stones built under each other at regular intervals, as shown in Figure 80, are bad, as they give the pressure no chance to spread, but keep concentrating it back onto the part of wall immediately under bond-stones, whereas, in Figure 81, the pressure is allowed to spread gradually over a larger area of the wall. Where, however, a heavy girder, column or other weight comes on a wall, it is distributed by means of a large block, generally granite or stone, or sometimes by a large iron plate.

The block or plate should have sufficient area not to crush the brick-work directly under it. Where girder-ends are built into walls, it is also desirable to build a block over the girder-end as well as under the same. The upper block prevents any part of the wall from resting on the girder or being affected by its shrinkage, if of wood; if the girder is of iron the upper block will wedge in the girder-end more firmly, and the girder will be able to carry more load. See page 57.

Use of bond-stones.

Use of bond stones

Fig. 80.

Anchors for girders and beams are usually made of iron and of such shape as to allow the girder or beam to fall out in case of fire. Anchors made of iron are not objectionable in inner walls, or where not exposed to dampness; all iron should be thoroughly painted, however, with red lead or metallic paint. Before painting, all rust should be scraped off. Don't believe the "practical" man who says the paint will stick better if you leave the rust on the iron; it will stick better to the rust, no doubt, but not to the iron. For outside work all iron should be galvanized; but it is better to use copper for anchors, dowels, clamps, etc. All copings should be clamped together, the clamps being counter-sunk. Slanting-work and tracery should be dowelled together. Where iron is let into stones, and run with lead or sulphur, the iron is apt to swell with rust or heat and burst the stone. Dampness in walls is one of the worst dangers, both on account of frost and decay. All exterior mouldings and sills should be projected and have "drip-moulds" cut underneath, to cause the water to drop or drip; this will prevent considerable dampness and keep the outside surface of the wall from becoming dirty, as the dust lodging on top of mouldings discolors the rain-water, and the latter, instead of streaking down the wall, will drop off.

Walls are frequently built hollow to prevent dampness, but this raises many objections. Shall the inner or outer wall be the thicker? If the outer wall, then all beams, etc., have to be that much longer, so as to rest on the stronger part; they are liable to transfer dampness, and then, too, the thicker, and, consequently, greater, part of wall is exposed to dampness. If the inner wall is thicker, the construction, so far as beams, etc., are concerned,

Metal anchors.


Hollow walls.

no doubt is better, but the outer part is apt to be destroyed by the frost. Then at windows and doorways both must be connected, and dampness is apt to get through. It is well to ventilate the air-space between walls, at the bottom from inside and at the top from on The bottom of spaces should be drained. Tops of arches, or lintels over openings, should be cemented and asphalted (in the air-space), to shed any dampness settling on them. The outer and inner walls should be frequently anchored together. Iron anchors galvanized, or copper anchors are best; they should have a half-twist', as shown, to prevent water running along them.

Walls And Piers 100153

Fig. 81.

Care must be taken to keep hollow walls free from hanging mortar, which will communicate moisture from one wall to the other.

But hollow walls are not nearly so good as solid walls with porous terra-cotta furrings.

Where walls are coped with stone, there should be damp-courses of slate or asphalt under same, and the back side should be flashed, to prevent dampness descending. If gutters are cut in stone cornices, they should be lined with metal, preferably copper, the outer edge being let into a ragde and run in with lead.

When a wall, already built, has to have its foundations carried down lower, it is called "underpinning the wall." Holes are made through the wall at intervals and through these (at right angles to the wall) are placed the "needles," that is, heavy timbers, which carry the weight of the wall. Where the needle comes in contact with the wall, small cross-beams are laid on its upper side, and wedged and filled with mortar, to get a larger and more even bearing against the wall. At the inner and outer ends of the needles heavy upright timbers are placed underneath, running down to the new, lower level. The foot or ground bearing of these timbers is formed by heavy planks crossing each other, to spread the weight over more ground; wedges are driven under the feet of the uprights, till the ends of the needle are forced up, and the centre of the needle shows a decided downward curve of deflection, indicating that the weight of wall is on the needle. Frequently jack-screws are used in place of wedges, to get the weight onto the uprights. As soon as the needles carry the weight of wall, the intermediate portions of wall are torn out and the excavating to the lower level begins. If the soil is loose, sheah-piling must be resorted to on each side of wall. Frequently the feet of the uprights are "cribbed," that is, sheath-piled all around, to hold the ground under them together and keep it from compressing. The new wall is built up from the lower level between and around the needles. On top of the new wall two layers of dressed-stone are placed idling up between the old and new work. Between these stones iron wedges are driven in opposite pairs, one from the inside and one from the outside. These wedges must be evenly driven from both sides or the wall might tip. These wedges are driven until the weight of the wall is on them and off the needles.