A softer stone, which can be dressed with the hammer, may be treated in two different ways: It may be shaped to fit closely, without using any spalls to fill up the interstices, and, thus, appear as a cut-out puzzle; this is called “cobweb rubble.” However, the more dignified treatment is the squared, uncoursed rubble, in which the blocks are cut to rectangular shape and the joints pointed with a tool. Figures 5 and 6 illustrate these. A wall built entirely of field stone depends upon the mortar for its strength. It appears the best when the joints of the surface are raked out, permitting a large part of the stones to project outward. Figure 7 illustrates this kind of rubble wall. When the rubble wall is built with very carefully squared stones, and in regular courses, it partakes more of the monumental character of ashlar work and draws away from the rustic value of rubble. In determining the amount of cutting which is to be done, the character of the building should be considered, remembering that the smoother and more finished the wall, the more monumental is its appearance. [Illustration: Fig. 6. Square uncoursed Rubble tooled joints Fig. 7. Field stone Rubble raked joints] [Illustration: Bond stone every 2' in ht. and 3' in length] MORTAR, BOND, AND THICKNESS [Illustration: Thickness of rubble-stone wall] The kind of mortar which should be used for the rubble wall depends upon its location and desired appearance. All foundation-walls, and all walls which are subject to dampness, should be built with Portland-cement mortar. Lime mortar may be used in walls above grade, although cement mortar, or cement-lime mortar is superior. As the strength of a rubble wall depends more upon the mortar than the bond, it is well to use the best. However, care should be taken that the wall is well bonded. A wall which consists of two faces, not bonded together, should not be built. A bond stone which carries through from one face to the other should be set into the wall every 2 feet in height, and every 3 feet in length. This bond stone should be flat and about 12 inches in width and 8 inches thick. The usual thickness of walls for dwellings not over three stories in height is 16 inches, and the foundation-walls are made 8 inches thicker than the wall above or 2 feet. The footings under a stone wall should be of concrete, not less than 12 inches thick, and should rest upon solid ground at a depth equal to, or greater than, the frost-line below the surface, unless solid rock occurs above this point. The width of the footings should be such that it projects outward on both sides of the wall at least 4½ inches. FURRING