STONE MASONRY.
Rubble. Of the different kinds of stonework, nibble masonry less preparation of the material than any other use of the stone, and covers a wide range of construction, from ordinary founda tion walls, such as we have already considered, to the handsome well-pointed masonry of churches and other build ings.
Two definite classes of rubble work are recognized : (1) uncoursed rubble, in which stones of irregular shape arc laid as they come to hand with no attempt at level courses, as in Fig. 133; and (2) coursed rubble, in which the blocks are lev elled off at regular heights to a horizontal bed, as in Fig. 134. A wall of rubble is finished by pointing up the joints with cement mortar colored to taste, usually to the same color as the stone, when this is at all even colored. Sometimes a false joint of red or white mortar is run upon this pointing to imitate ashlar work.
[ncoursecl rubble is sometimes laid with irregular pieces haying hammered joints which are fitted together with no "spills," or small stones, between. (Fig. 135.) This is an expensive and tedious process but is very effective when well done. The coursing of rubble is not necessarily uniform, or at the same level throughout, but may rise and fall by level stages to accommodate the size of the materials.
The superintendence of this class of work, beyond a general inspection of the duality and soundness of the stone, will be mainly to see that the stones are well laid after being suitably prepared by roughly squaring with a hammer, and knocking off all weak angles and projections. The stones should be clean and free from dust, curl should be moistened before laving. Mortar should be used in sufficient quantities io permit of each stone being firmly imbedded, and all hol lows between the large stones should be filled with small stones carefully bedded in the mortar. :\ 11 large stones should be laid on their natural bed, and should le so used that the side parallel to the bed shall be the largest, so that the stones shall lie flat and in no ease be set on edge or on end. Care must be taken to break joints, and no side joint should form an angle with the bed of less than (30 degrees.
The bonding of a rubble ;gall must be carefully watched, and bond stones freely used. If the rubble is backed with brick, as is often the case, iron clamps and ties should be inserted, which may run through the wall and turn lip up behind the brick, if the back of the wall is to be concealed, and they should run to the inside course of bricks in any case.
(Fig. 13f3.) If nibble is used
as a backing for cut stone, the facing should contain a large proportion of thick st',ues which .will bond Well with the rubble. These bond stones may be left rough at the back and sides, but the upper and lower beds should be level, so that they will have no tendency to Avedge off the backing. '.I'lii.s backing should he carried up at the same time as the Face work with the coursing leveled off at the some place. a good proportion of thick stones running two-thirds or more across the thickness of the wall is better than a fear extending through the wall.
Ashlar Masonry consists of blocks of ,stone which have been cut to a regular figure, generally rectangular in shape, and laid in courses of usually a foot or more in height. (Fig. 137.) If the courses are not maintained at the level con tinuously, but are laid of stones of unequal height but still level and plumb, the Nyork is called "broken ashlar," shown in Fig. 13S.
In all ashlar work of soft material, such as limestone, no stone should have a length greater than three times its height. In harder stone the length may he four or five tunes the The thickness in soft stone may be once-and-one-half or twice the height; in hard stone, three times the height.
Laying. The heel capon which the stones are laid should be level, and cleared of dust or refuse, and vveil moistened with water. Upon this the bed of mortar is spread evenly. Wooden wedges of the thickness of the joint are then laid on the face of the bed, and the stone carefully ered upon the wedges, to be moved into exact position by the aid of a "pinch bar." In using a bar or rolk.rs in ling cut stone, it will be essary to protect the edges of the stone by bagging or other "softening." When the .stone is in its final position, the wedges may be removed and the stone settled into place and leveled by striking with a wooden mallet. In the case of heavy stones where there would be danger of the weight of the stone squeezing the mortar out of the joint, the wooden wedges are allowed to remain until the mortar has set. The bed of mortar should he kept back un inch or so from the face of the stone, so that the stone shall not hear on its outer edge. This will save raking out the mortar when the wall is to be pointed, and will prevent anv dan ger of the splitting off of "spalls on the face, which might occur on account of the mortar on the face of the joint becoming hard sooner than the inside, when the unequal settlement would bring pressure on the edge of the stone.