Squared-Stone Masonry

SQUARED-STONE MASONRY. This is masonry in which the joints are more than one half inch thick and less than about one inch ($ 552). Squared-stone masonry may be classified according to the finish of the face as either quarry-faced or pitch-faced, and according to the arrangement of the courses as range, broken range, or random. The quoins and the sides of openings are usually reduced to a rough-smooth surface with the face-hammer, the ordinary ax, or the tooth-ax. This work is a necessity where door or window frames are inserted; and it greatly improves the general effect of the wall, if used wherever a corner is turned.

Squared-stone masonry is distinguished, on the one hand, from ashlar in having less accurately dressed beds and joints; and, on the other hand, from rubble in being more carefully constructed. In ordinary practice, the field covered by this class is not very definite. The specifications for "second-class masonry" as used on some railroads usually conform to the above description of quarry— faced range squared-stone masonry; but sometimes this grade of masonry is designated "superior rubble." Squared-stone masonry is employed for the piers and abutments of highway bridges, for small arches, for box culverts, for basement walls, etc.

Backing.

The statements concerning backing of ashlar ($ 564) apply substantially to squared-stone masonry.

_ _ _ Pointing.

As the joints of squared-stone masonry are thicker than those of ashlar, the pointing should be done propor tionally more carefully; while as a rule it is done much more care lessly. The mortar is often thrown into the joint with a trowel, and then trimmed top and bottom to give the appearance of a thinner joint. Such work is called ribbon pointing. Trimming the pointing adds to the appearance but not to the durability. When the pointing is not trimmed, it is called dash pointing.

Specifications. The specifications for squared-stone masonry should be about as follows: The stones shall be of durable quality; and shall be free from seams, powder cracks, drys, or other imperfections.

The courses shall be not less than 10 inches thick.

Stretchers shall be at least twice as wide as thick, and at least four times as long as thick. Headers shall be at least five times as long as thick, and at least as wide as thick. There shall be at least one header to three stretchers. Joints on the face shall be broken at least 8 inches.

The beds and the vertical joints for 8 inches back from the face of the wall shall be dressed to make joints one half to one inch thick. The front edge of the joint shall be pitched to a straight line. All corners and batter-lines shall be hammer-dressed.

The backing shall consist of stones not less in thickness than the facing.

At least one half of the backing shall be stones containing at least 2 cubic feet. The backing shall be laid in full mortar beds; and no spalls shall be allowed in the bed joints. The vertical spaces between the large stones shall be filled with spalls set in mortar.

The coping shall be formed of large flat stones of such thickness as the engineer may direct, but in no case to be less than eight inches. The upper surface of the coping shall be bush-hammered, and the joints and beds shall be dressed to one half inch throughout. Each coping stone must extend entirely across the wall when the wall is not more than four feet thick.

Amount of Mortar Required.

The amount of mortar required for squared-stone masonry varies with the size of the stones and with the quality of the masonry; and will be a little more than twice that required for ashlar—see § 567.

For quantities of cement and sand required for mortars of various compositions, see Table 22, page 120.