Ashlar masonry consists of blocks of stone cut to regular figures, generally rectangular, and built in courses of uniform height or rise, which is seldom less than a foot.
Size of the Stones. In order that the stones may not be liable to be broken across, no stone of a soft material, such as the weaker kinds of sandstone and granular limestone, should have a length greater than 3 times its depth or rise; in harder materials the length may be 4 to 5 times the depth. The breadth in soft materials, may range from 11 to double the depth; in hard materials it may be 3 times the depth.
Laying the Stone. The bed on which the stone is to be laid should be thoroughly cleansed from dust and well moistened with water. A thin bed of mortar should then be spread evenly over it, and the stone, the lower bed of which has been cleaned and moistened, raised into position, and lowered first upon one or two strips of wood laid upon the mortar bed; then, by the aid of the pinch bar, moved exactly into its place, truly plumbed, the strips of wood removed, and the stone settled in its place and levelled by striking it with wooden mallets. In using bars and rollers in handling cut stone, the mason must be careful to protect the stone from injury by a piece of old bagging, carpet, etc.
In laying " rock-faced " work, the line should be carried above it, and care must be taken that the work is kept plumb with the cut margins of the corners and angles.
The Thickness of Mortar in the joints of well executed ashlar masonry should be about I of an inch, but it is usually about 1. Amount of Mortar. The amount of mortar required for ashlar masonry varies with the size of the blocks, and also with the closeness of the dressing. With x to 1-inch joints and 12 to 20-inch courses will be about 2 cubic feet of mortar per cubic yard; with larger blocks and closer joints, there will be about 1 cubic foot of mortar per yard of masonry. Laid in 1 to 2 mortar, ordinary
ashlar will require to of a barrel of cement per cubic yard of masonry.
Bond of Ashlar Masonry. No side joint in any course should be directly above a side joint in the course below; but the stones should overlap or break joint to an extent of from once to once and a half the depth or rise of the course. This is called the bond of the masonry; its effect is to cause each stone to be supported by at least two stones of the course below, and assist in supporting at least two stones of the course above; and its objects are twofold: first, to distribute the pressure, so that inequalities of load on the upper part of the structure, or of resistance at the foundation, may be transmit ted to and spread over an increasing area of bed in proceeding down wards or upwards, as the case may be; and second, to tie the structure together, or give it a sort of tenacity, both lengthwise and from face to back, by means of the friction of the stones where they overlap. The strongest bond in ashlar masonry is that in which each course at the face of the wall contains a header and a stretcher alternately, the outer end of each header resting on the middle of a stretcher of the course below, so that rather more than one-third of the area of the face consists of ends of headers. This proportion may be devi ated from when circumstances require it; but in every case it is ad visable that the ends of headers should not form less than one-fourth of the whole area of the face of the wall.