79. Filling of Voids

All stones, large and small, should be solidly bedded in mortar, and all chinks or interstices between the large stones should be partially filled with mortar and then with small pieces of stone, or spalls, driven into the mortar with the trowel, and then smoothed off on top again with mortar.

Many masons are apt to build the two faces of the wall with long, narrow stones and fill in between with dry stone, throwing a little mortar on top to make it look well.

A horizontal section through such a wall would appear as shown in Fig. 41. Such a wall would require but little loading to cause the outside faces to bulge, owing to the lack of strength in the middle portion. The way in which a wall of irregular shaped stones should be built to get the most strength is shown in Fig. 42.

Such a wall requires no more stone than the other, but requires more lifting and a little more use of the hammer, and these appear to be the real reasons why better work is not more generally done.

79 Filling of Voids 10040

Fig. 39.

79 Filling of Voids 10041

Fig. 40.

80. Window Openings

If there should be a window or door opening in the foundation wall, as in Fig. 43, the stones just below the opening should be laid so as to spread the weight of the wall under the opening, as shown by the stones ABC. If there is to be any great weight come upon the foundation it will be better not to build the window sills into the wall, but to make their length just equal to the width of the opening, or slip sills, as they are called, then there will be no danger of their breaking by uneven settlement of the wall.

Occasionally part of the foundation wall of a building goes down much lower than the adjoining portion, and, as there is almost always a slight settlement in the joints of the wall, unless laid in cement the deeper wall will naturally settle more than the other, and thus cause a slight crack. This can be avoided by building the deeper wall of larger stone, so that there will be no more joints than in the other wall, or by making thin joints and using cement mortar.

80 Window Openings 10042

Fig. 41.

80 Window Openings 10043

Fig. 42.

80 Window Openings 10044

Fig. 43.

81. Thickness of Foundation Walls

The thickness of the foundation wall is usually governed by that of the wall above, and also by the depth of the wall.

Nearly all building regulations require that the thickness of the foundation wall, to the depth of 12 feet below the grade line, shall be 4 inches greater than the wall above for brick and 8 inches for stone, and for every additional 10 feet, or part thereof deeper, the thickness shall be increased 4 inches. In all large cities the thickness of the walls is controlled by law. For buildings where the thickness is not so governed the following table will serve as a fair guide:

Table VI. - Thickness For Foundation Walls

HEIGHT OF BUILDING.

DWELLINGS, HOTELS, ETC.

WAREHOUSES.

BRICK.

STONE.

BRICK.

STONE.

Ins.

Ins.

Ins.

Ins.

Two stories......................

12 or 16

20

16

20

Three stories......................

16

20

20

24

Four stories......................

20

24

24

28

Five stories......................

24

28

24

28

Six stories......................

24

28

28

32

Only block stone, or first-class rubble, with flat beds, should be used in foundations for buildings exceeding three stories in height. The footings should be at least 12 inches wider than the width of the walls. (See Section 66.)

In heavy clay soils it is a good idea to batter the walls on the outside, making the wall from 6 inches to a foot thicker at the bottom that it is at the top, and plastering the outside with cement. (See Fig. 3, Section 10.)