Definitions of Hinds of Masonry

Other Classifications.

The preceding classification is based on the quality c f the masonry; but railway engineers sometimes classify masonry according to its use,—as bridge masonry, arch masonry, culvert masonry, etc. However, it is more logical and also more expressive to use the classification according to quality, and if desired add a term to indicate the purpose of the masonry, as, for example, arch ashlar masonry, bridge squared-stone masonry, culvert rubble. However, the terms defined in 4 548-53 are suffi cient to give a reasonably complete definition of any ordinary kind of masonry. The following are examples of the method of using these terms: pitch-faced random ashlar masonry, or bush-hammered range ashlar masonry; quarry-faced broken-range squared-stone masonry; coursed rubble masonry.

Formerly, railway engineers frequently classified masonry as first-class, second-class, and third-class, which corresponded approx imately to ashlar, squared-stone, and rubble respectively; but such a classification is now seldom used.

Dry Masonry.

The three preceding classes of masonry, ashlar, squared-stone and rubble, are laid with mortar; and there are three other grades of what may be called dry masonry, which are laid without mortar. These are slope-wall masonry, stone paving, and riprap.

Slope-wall Masonry. A thin layer of dry masonry, built against the slope of embankments, excavations, river banks, etc., to preserve them from rain, waves, or weather.

Stone Paring. Dry masonry used for the inverts of culverts, for protecting the lower end of culverts from undermining, for foundations for stone-box culverts, etc.

Riprap. Stone thrown in promiscuously about the base of piers, abutments, etc., to prevent scour, or placed on banks of rivers and canals to prevent wash.

The following general principles apply to all classes of stone masonry.

1. The largest stones should be used in the foundation to give the greatest strength and lessen the danger of unequal settlement.

2. A stone should be laid upon its broadest face, since then there is better opportunity to fill the spaces between the stones.

3. For the sake of appearance, the larger stones should be placed in the lower courses, the thickness of the courses decreasing gradually toward the top of the wall.

4. Stratified stones should be laid upon their natural bed, i.e., with the strata perpendicular to the pressure, since they are then stronger and more durable.

5. The masonry should be built in courses perpendicular to the pressure it is to bear.

6. To bind the wall together laterally, a stone in any course should break joints with or overlap the stone in the course below; that is, the joints parallel to the pressure in two adjoining courses should not be too nearly in the same line. This is briefly comprehended by saying that the wall should have sufficient lateral bond.

7. To bind the wall together transversely, there should be a con siderable number of headers extending from the front to the back of thin walls or from the outside to the interior of thick walls; that is, the wall should have sufficient transverse bond.

8. The surface of all porous stones should be moistened before being bedded, to prevent the stone from absorbing the moisture from the mortar and thereby causing it to become a friable mass.

9. The spaces between the back ends of adjoining stones should be as small as possible, and these spaces and the joints between the stones should be filled with mortar.

10. If it is necessary to move a stone after it has been placed upon the mortar bed, it should be lifted clear and be reset, as attempting to slide it is likely to loosen stones already laid and destroy the adhesion, and thereby injure the strength of the wall.

11. An unseasoned stone should not be laid in the wall, if there is any likelihood of its being frozen before it has seasoned.