This section is from the book "The Building Trades Pocketbook", by International Correspondence Schools. Also available from Amazon: Building Trades Pocketbook: a Handy Manual of reference on Building Construction.
Stone being the stronger material, a wall should have as much stone and as little mortar as possible. Contact of the stones in bed joints is not advisable, as the shrinkage of the mortar may leave them bearing only on the projecting angles. The thickness of joints in stonework is from 3/16 to 1/2 or 5/8 in., depending on the class of work; but for ordinary ashlar, the usual thickness is about 1/4in., and more in rough masonry. Bed joints should be full and square to the face, as if worked slack at the back - to make thin face joints-spalls are likely to break off at the front edges. Good bonding is essential for a strong wall, and the proper placing of headers should be carefully watched. Long pieces of stone should be well supported and bedded to prevent breaking; pieces more than, say, four times the thickness, should not be used. Stone, especially if stratified, should be laid on its natural or quarry bed, as if set vertically, water easily penetrates between the layers, and, freezing, splits off the outer ones. For damp places, stonework (and brickwork) should be laid in cement mortar or lime-and-cement mortar, while in dry positions good lime mortar may be used. In laying stone, the mortar should be kept back about an inch from the face of the wall; otherwise spalls may be broken off, owing to the outside mortar hardening more rapidly than that in the interior, settlement bringing the pressure on the hard layer. This precaution is very important in the case of lug sills, band courses, etc. The joints may be pointed, after the wall is built, with some non-staining mortar.
The value of grouted walls is a much disputed point. A wall grouted with thin lime mortar undoubtedly requires a long time to dry thoroughly, while if the grout is thick, it does not fill every crevice. With cement grout, however, a wall so filled is very much stronger than one laid with stiff mortar, as has been shown by tests. When using cement grout, the brick or stone should not be wet; they will then absorb the water in the grout, and also some of the cement, thus increasing the adhesion. Grout is usually made of ordinary mortar, thinned to the consistency of cream. If an extra strong wall is required, a 1-to-l mortar may be used.
Ashlar should be carefully bonded, either by using courses of different thickness, or, if the ashlar is only from 2 to 4 in. thick, by means of wire ties and anchors, such as are shown in Fig. 11. When the courses are from 4 to 8 in. thick, a good bond to the backing may be had by using each thickness in alternate courses. When the backing is brick, the joints in it should be as thin as possible; and if lime mortar is used, some cement should be added, to prevent shrinkage. Very thin ashlar must not be considered in determining the strength of walls, but the backing must be made sufficiently strong, independent of the ashlar. All projecting courses, such as cornices, lintels, sills, etc., should be beveled on top, and have a drip cut on the under side, as shown at a, Fig. 6, to prevent water from soaking into the joints. Lug sills should only be beveled between the jamb lines, the ends being cut level, as at 6, thus keeping out water from the joint between brick and stone, and also forming a more secure bearing for the wall. The top of exposed walls should be covered by coping, in long pieces, and have the vertical joints well filled with good mortar. Gable copings should be anchored very firmly, either by iron dowels or ties, or by bond stones, the latter method being shown in Fig. 7. _______