The same defect may oc cur if the bed of the stone is cut hollow or slack, as in Fig.
131, when the settlement of the mortar will brine the whole pressure upon the front edge of the stone with the sane result. For this reason, care should be taken that the bed joints arc square and trite. Door and window sills should be bedded only under tlieir ends, as the natural settlement will cause them to break if bedded under the opening.
(Fig. 140.) Stone work in damp situations should be set in cement mortar, but lime may be used if the situation is dry. Limestone and marble, and some sandstones, are often badly stained by the use of cement mortar, and in respect to this should always be made before using an unfamiliar stone.
In case of danger from this source, Lafarge cement, a cement made of lime, plaster of Paris, :ntd marble dust, may be used, which should be plastered over the back of the stone as well, if cement must be used in the hacking.
Bonding. Care must be taken that no vertical joint in any course conies over a joint in the course below, but the stones should break joints or overlap, preferably to an extent of from once to once and-a- half the height of the course, so that melt stone will be sup ported by at least two stones of the course below, and will in turn support at least two stones of the above. This will not only distribute the pressure of the weight above, but will tie the wall together in its length, by means of the friction of the stones where they overlap. For the same reason, the thickness of the stones should vary, so as to make a bond in and out of the wall, as in Fig. 141, and at least one stone in every ten square feet of wall should be the full thickness. The strongest bond in a wall of cut ashlar is one in which each course contains a header and stretcher alternately, the outer end of each header coming on the middle of the stretcher. (Fig. 142.) In broken ashlar work the bond should he carefully preserved, nud, in the case of broken ashlar used with a brick backing, it will he convenient to use stones of a thickness of four, eight, and twelve inches, alternating, so that the bond may be obtained through and through without much cutting of the bricks.
In the hacking of ashlar, the joints•of the brickwork should be made as thin as possible, and cement should be used to pre vent shrinkage of the joints, which will necessarily be more numerous than the joints of the ashlar facing. Brick
backing should not be less than eight inches thick, and, if the facing is in courses ex ceeding a foot in height, each large piece should be tied to the brick by iron clamps in the proportion of abort every three feet in the length of the wall, and two feet in the height. It will be of advantage in this class of work if the horizontal joints are not allowed to run to a great length. Changing the level of the every four or five feet. will make a good looking wall. Broken ash lar is usually prepared at the building site, but it will be a saying if the stones are cut to the required heights in the yard, leaving only au end joint to be cut at the building.
Quoins, Jambs and Lintels. The corner stones of a building are called quoins, and they are often given prominence over the face of the wall, as in Fig. 143. In broken auh]ur the quoins should be as large in height as the of the wall stones. Stones at the sides of openings are called jamb stones and are often used in a manner similar to quoins. Lintels or caps are the stories which cover door or window openings. They are usually in one piece, as in Fig. 111 A, bnt are sometimes nec essarily jointed. (Fig. 144 B.) In this case the joints should be "toggled" as shown. If the lintel spans an opening which is too great for its carrying capacity, it may be assisted by the use of a ,steel angle-bar or beam. (Fig. I4..) Lintels should liear at the ends at least four inches, and in the case of the lintel being thicker than the jamb, it should have bearing enough to reach beyond any recess which the window frame may require, as in Fig. 146, so that the inside of the lintel will be Supported. • Columns, Arches and Trimmings. Columns, where the material will allow, should be cut in one piece with separate capitals and bases, and great care should be taken in emitting, and also in setting, to have the lied joints per fectly level to the axis of the column. Clear cement mortar should be used for setting, and especial care taken to keep the outside of the joint empty for a depth of at least of an inch, to prevent chipping the column. I,iniels or cornices over (.ohni ns are often exposed oil both sides and should be (lit from one stone if practicable; if not, they may be built up as shown. (Fig. 147.) In this case the stones should be carefully tied and clamped together.