98. Stone foundation walls below ground, when concealed from outside view, are usually constructed of rough rubble, as shown in Fig. 34. This represents an elevation (a) and section (b) of a 20-inch rubble stone wall, shown at a, a, 10 feet high, with footing stones b, 8 inches thick, and 2 feet 8 inches wide.

Stone Rubble Foundation Walls 36

Fig. 34.

99. Stone foundation walls should be bonded together, as shown in Fig. 35, where a shows the bond stone, or header, and b the stone foundation wall. All stone walls, 24 inches or less in thickness, should have at least one header extending through the wall, every 3 feet in height, and in every 4 feet of length. If the stone wall is over 24 feet in length, there should be at least one header for every 6 superficial feet of wall space, running into the wall at least 2 feet. The headers should not be less than 18 inches in width and 8 inches in thickness, and should be good, flat stone. These headers serve to bind the stones of the walls together, and keep the foundation from splitting apart crosswise when weight is placed upon it.

100. Fig. 36, at a, a, shows vertical joints coming one above another through three or four successive outside courses. This should never be allowed, but the joints of the stonework should be broken, as shown in Fig. 34.

Stone Rubble Foundation Walls 37

Fig. 35.

Stone Rubble Foundation Walls 38

Fig. 36.

Stone Rubble Foundation Walls 39

Fig. 37.

Where a long vertical joint occurs, the weight of the wall above may cause the wall to settle more on one side of the joint than on the other, and produce serious rupture.

101. All wall angles should be well tied by long stones laid alternately in the wall, as shown at a, Fig. 37, the long angle stones tying the wall at that point. By using these long stones, the weight on the corners of the wall is more equally distributed, and the wall can be kept plumb and true.

102. Foundation stone should always be laid on their natural or quarry beds. The tendency to splitting or cleavage in a stone is with the grain or bed; so when the stone is laid on the original bed, the weight of the material placed above it comes against the grain of the stone. No stone should have more face than bed, and one side, at least, of each stone should be reasonably flat. Every stone laid should be well bedded in mortar.

103. The usual practice with masons in rough walling is, after setting the larger stones, to fill the interstices with spalls or chips of stone, or even pebbles, more or less carefully fitted, and put in dry; then to dash in mortar, trusting it will work its way into the crevices. It does so to some extent, but the method is not a good one. A good, conscientious workman will place no stone, even the smallest chip, except in a bed of mortar prepared to receive it, rubbing it well in, and settling it with blows of the trowel and hammer; again driving smaller fragments into the mortar, which is squeezed up around it; so that all the stones have a layer of mortar between them.

A good plan is also to grout the walls with mortar, made so thin that it will flow into the spaces, and interstices, between the stone.

104. For good work, it is necessary that the outside of the wall (even when concealed by the excavated bank) should be carried up with a good face, as shown in Figs. 34 and 37, and the joints well filled with either cement, or lime-and-cement mortar. If this is properly done, any moisture that runs out from the bank or descends from above, so as to flow down over the outer face of the wall, will drip off, instead of running into the joints.

105. The space between the outside of the foundation and the bank of the excavation should be filled in with gravel or sand (preferably the former), well packed down. Thus in Fig. 38, a shows the space between the foundation wall and the bank, while b is the stone wall. This method makes the cellar drier and warmer, and keeps much of the moisture away from the foundation walls.

Stone Rubble Foundation Walls 40

Fig. 38.