Rubble Stone

Rubble stone, or quarry stone, is stone in the form of irregular pieces or slabs, used primarily for laying foundations. It is obtained, mainly, from limestone and sandstone. The most extensive deposits of such limestone in the USSR are located along the banks of the Tosna River near Leningrad, in the Volkhov River region, in the vicinity of Moscow, in the Zhiguli Mountains on the Volga, near Sevastopol, etc. Sandstones are common near Lake Onega, near Moscow, and in many other places. Good rubble stone should be as little hygroscopic as possible, possess the lowest volumetric weight, and not be taken from the upper strata, which are often contaminated with organic substances. To avoid cracking in the masonry, the rubble stone must be frost-resistant. Depending on the rock type, rubble stone often possesses various physical properties, which serves as a major defect when using it as a building material for the walls of residential buildings. Rubble masonry is used, primarily, in parts of structures that do not have visible surfaces, such as: foundations, walls that have exterior cladding, etc. The basic requirement for high-quality rubble masonry is that each stone must be surrounded on all sides by binding mortar; in view of this, rubble masonry must be performed "by the trowel" and not "by pouring," because in the latter case, the stones squeeze the liquid mortar out from under themselves and, settling onto the underlying stones, do not connect with them at all. Rubble masonry for residential houses is used in areas rich in rubble stone deposits and with a mild climate (the south of the USSR). The defects of these walls consist of their significant thermal conductivity (the coefficient of thermal conductivity of dry rubble masonry is 1.7), low heat capacity, and rather significant hygroscopicity. The air permeability of rubble stone is close to the air permeability of brick. In rural construction, a primitive type of masonry is used for residential houses, using clay thinned with sand. In this form, rubble masonry depends significantly on the mortar (clay), which occupies up to 40% of the volume. Such a wall is subject to severe erosion in the joints by rain if it is not covered on the outside with plaster, and, according to data on the Crimean earthquake of 1927, it is completely non-seismic resistant.