Figure 4-27. - Coursed rubble masonry

approximately continuous horizontal bed joints, as shown in figure 4-27.

The stone used in stone masonry should be strong and durable. Durability and strength depend upon the chemical composition and physical structure of the stone. Some of the more commonly found stones that are suitable are limestone, sandstone, granite, and slate. Unsquared stones obtained from nearby ledges or quarries or even fieldstones may be used. The size of the stone should be such that two people can easily handle it. A variety of sizes are necessary to avoid using large quantities of mortar.

The mortar used in stone masonry may be composed of portland cement and sand in the proportions of 1 part cement to 3 parts sand by volume. Such mortar shrinks excessively and does not work well with the trowel. A better mortar to use is portland cement-lime mortar. Mortar made with ordinary portland cement will stain most types of stone. If staining must be prevented, nonstaining white portland cement should be used in making the mortar. Lime does not usually stain the stone.