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Miscellaneous Masonry Products: Building Stone
1) Geological Source
2) Quarrying
3) Classification By Form And Type
4) Physical Properties
5) Finishes
Introduction
Building stone must be included among the oldest building materials known to man. Throughout recorded history, stone has been regarded as the preferred material in the construction of permanent buildings. This is doubtless due to its unique qualities --beauty, permanence, workability and accessibility, among others. It was, in fact, the predominant material used in the construction industry prior to the turn of the twentieth century.
Since that time, stone has assumed a new role in the construction field. Because the height of buildings continued to increase, it became necessary to look more closely at the mass of the materials that went into the basic structures. Stone began to be developed as a facing material, rather than as a basic structural material.
In this new role it is used as a veneer, in comparatively thin slabs, over a building frame of reinforced concrete or steel. In this way, the inherent qualities which initially brought stone into prominence -- beauty, permanence, adaptability and economy -- are used without having to contend with the great mass imposed by a solid stone structure.
1. Geological Source
An understanding of the geological origin of building stones, their structure and composition may be an aid in choosing stone that will fit properly into the regional setting and with the particular architectural design proposed for a specific building. Such an understanding may also be helpful in the selection or rejection of a particular stone proposed for a job and in the correct placing of each selected unit during the stone-laying process.
Rock may be divided into three broad categories depending on its geological origin; namely, sedimentary, igneous and metamorphic.
1.1. Sedimentary rock was formed by the action of water. This action may have resulted either in the depositing of minerals at the bottom of a body of water through sedimentation or in depositing them on the earth's surface. The latter action takes place when water flows to the surface from the interior of the earth, bringing dissolved minerals that are deposited on the surface by evaporation.
Sedimentary rock, like the other groups, has extensive range of composition and character, but for our purposes it is possible to divide it into four groups. These are: rudaceous rock, which includes breccia and conglomerate; arenaceous rock, which includes sandstone, arkose and quartzite; argillaceous rock, largely shale; and calcareous rock, which includes a number of limestones.
1.2. Igneous rock was formed by the cooling and consolidation of molten matter that was brought to the earth's surface by volcanic action. It may be divided into three main rock types: volcanic, which includes pumice, obsidian, rhyolite, andesite and basalt; hypabyssal, which includes felsite, quartz, porphyry and dolerite; and plutonic, encompassing granite, diorite and gabbro.
1.3. Metamorphic rocks are distinctive new rock types that have been changed from their original igneous or sedimentary structure by the action of extreme pressure, heat, moisture, chemical fluids or various combinations of these forces. There are a great many of these metamorphic rocks, but only two groups have much significance as building stone, namely the slates and the marbles. A slate is a rock derived from argillaceous sediments or volcanic ash by metamorphism, It has very distinct cleavage lines along planes that are quite independent of the original bedding. A marble is a granular limestone, recrystallized by heat or pressure.
1.4. Rock may also be classified according to its composition. A great many minerals occur in rock formations throughout the world, but stone used for construction purposes generally comes from rock that falls into one of three classifications: rock that contains mostly silica, rock composed largely of silicates and rock containing calcareous minerals.
Silica, which is the oxide of the element silicone, is the most abundant mineral on the earth's surface. It is the chief ingredient of sand and is found in most clays and in a number of the building stones. Free silica, of which crystalline quartz is the most common form, either alone or in combination with other elements, comprises about 60 percent of the earth's crust.
Silicates are minerals that are compounds of silica and one or more other elements and are the main ingredients of igneous rock. The quantity of silica in igneous rock varies from about 30 to 80 percent and is sometimes used as a method of classification of such rock. For example, igneous rock containing more than 66 percent silica is known as acid igneous rock, while basic igneous rock contains between 30 and 52 percent silica, with no free quartz. Intermediate igneous rock has a silica component of between 52 and 66 percent.
Silicate minerals include feldspar, hornblende, mica, and serpentine. Feldspar is a silicate of alumina in combination with lime or potash. Depending on the combination, colors may be red, pink or clear. Hornblende is a silicate of alumina with lime or iron. It is a tough, strong mineral appearing in green, brown and black crystals. Mica is mostly silicate of alumina but may occur in combination with other minerals such as iron or potash. It appears in soft, usually clear crystals that split easily into flat flakes. Serpentine, which is a silicate of magnesia, often appears in combination with lime. It is light green or yellow in color and has no readily defined planes along which it will split.
Included among the most common calcareous minerals are calcite, which is basically carbonate of lime and dolomite, a carbonate of lime in combination with varying amounts of magnesia.
2. Quarrying
The removal of stone from its natural bed is carried out by a process known as quarrying. The method of quarrying will depend to a considerable extent on the kind of stone being removed and the nature of the particular stone involved.
Quarry marble
Some stone deposits have natural horizontal divisions (i.e., they are stratified horizontally), and the horizontal lines of demarcation between the strata are known as bedding planes. Other types of stone will have more visible vertical separations, which are know as cleavage lines. In some stone, both are apparent.
2.1. These natural planes of separation are an aid in removing the stone from its natural location.
In one method of quarrying, holes are drilled close together at right angles to the bedding planes, cleavage lines, or both and wedges are driven into the holes to split the rock along the drilled line.
The layout for another method that involves quarrying on a large scale is illustrated. After the overburden has been removed, a channel machine or a rock saw is brought in to outline the boundaries of the quarry.
The channel machine is a heavy machine with a pneumatically-operated chisel mounted on one side which cuts a narrow channel into the rock, while the rock saw is simply a huge circular saw with diamond-studded teeth. These machines, traveling on temporary tracks, cut a single or double cut, depending on the subsequent method of operation, up to 3m (10 ft) deep, down each side and down the center of the area of exposed stone.
When a double cut is made, the material between the two cuts is split into blocks and removed to leave a canal, the depth of the cuts, down the sides and center of the quarry.
2.2. Then, using the channel machine, rock saw or a wire saw, lateral cuts are made and the long blocks thus produced are cut into convenient lengths and removed from the quarry bed for transportation and further processing.
A wire saw is a 6mm (1/4 in) diameter, endless wire, strung between pulleys which are mounted on a frame. The wire transports hard sand that acts as the cutting agent. It is when this method of cutting is used that the canals are required. The wire saw support frames are set in the canals, and the wire saw cuts across the span from side to center canal.
Diagram of limestone quarry layout
2.3 Finishing and preparation. The large blocks of stone from the quarry are taken to a mill where they are first passed through a gang saw that cuts them into thick slabs. Power saws (chat saws, shot saws and diamond saws) are then used to cut the slabs into pieces of the required dimensions.
Each piece is then given whatever surface treatment is required to produce the texture specified in the order. In some cases, the surface produced by the saw is all that is required. In other cases, planers, grinders, polishers or hammer and chisel are used to produce the desired texture.
Stones which are to be anchored to the building must be drilled either on the edge or the back, depending on their position. Those that have a special shape are produced by stone carvers, working with a hand-sized air hammer and chisel.
3. Classification By Form And Type
Stone for building purposes may be classified according to the form in which it is available commercially. These are: rubble (fieldstone), dimension (cut stone), flagstone (flat slabs) and crushed rock.
The stones which are most commonly used in modern building construction include: argillite, granite, limestone, natural lavas, quartzite, travertine, marble, schist, serpentine, sandstone and slate.
3.1. Rubble includes rough fieldstone that may simply have been broken into pieces of suitable size, or it may include irregular pieces of stone that have been roughly cut to size.
Canal along sides of stone bed
3.2 Dimension Stone makes up the largest portion of the stone used in building construction. It consists of pieces that have been cut to some specific dimensions and, in general, falls into two categories. The first consists of units of relatively small size, cut to various dimensions, and generally referred to as ashlar. This type of cut stone is used as a facing over a structural backup wall.
3.3 Flagstone consists of thin sheets of stone 12 mm (1/2 in) and up -- that may or may not have their face dimensions cut to some particular size. Such stone is used for flooring, patios, walks, and so forth.
3.4. Crushed stone consists of pieces varying from 10 to 150 mm (3/8 to 6 in) in diameter, It is used as coarse aggregate in the concrete industry and as a facing material for some architectural precast concrete curtain wall units.
3.5. Argillite. Argillite is a metamorphic rock, formed from clay, that normally has well-defined cleavage lines, It is produced as ashlar and rubble-facing stone, as floor tile and stair treads, wall base, coping stones, window stool and sills. Colors range from deep red to purple; a deep blue color with faint shades of green is common along with seam face colors of gray, buff, tan and russet.
The NW Masonry Guide Table of Contents
Masonry Institute of Washington
Washington State Conference of Mason Contractors
