Properties of natural stone for finishing facades
If you have decided to use only natural materials in the finishing of your own house, it is worth knowing a little more about them. Natural stones - a thing of status and beauty, but rather demanding to the conditions of exploitation and expensive. In today's issue we offer our readers to get acquainted with the aspects that must be kept in mind when choosing a stone for decoration.
What kind of stone is natural?
Stone is a rock and is made up of minerals and their associations (associations). Natural stone is a durable, strong, wear-resistant, resistant to external conditions material. It differs from artificial stone in origin, composition, environmental friendliness and some qualities.
It is not necessary to remember by heart how this or that rock appeared, but you can greatly simplify your choice, knowing that the origin of all rocks are divided into primary (igneous), secondary (sedimentary) and metamorphic (modified). Their general characteristics determine the groups of stones suitable for facades or interiors, because their origin determines many of their properties.
Eruption rocks came directly from molten magma. Granites, syenites, gabbro and labradorites are the result of cooling of magma at high pressure inside the Earth's crust; they are called deep rocks or igneous rocks and are characterized by their density and full-crystalline structure. Outcrops, that is, rocks formed at low temperature and pressure on the surface of the earth, usually have a fine crystalline structure and great porosity. These are basalts, porphyries, volcanic tuffs, ashes, and pumice stones.
Sedimentary rocks are the result of the destruction of primary, in the process of drying up bays, seas and lakes, and the decay of plant and animal remains. Common characteristics of these rocks are porosity, fracturing, and solubility in water. So emerged travertine and dolomite are used in finishing works. Organic sedimentary rocks include limestone. The clastic sedimentary rocks that are also widely used in finishing include sandstones, breccias and conglomerates.
Metamorphic rocks are the result of the transformation (metamorphosis) of igneous and sedimentary rocks into a new kind of stone under the influence of pressure, high temperature and chemical processes. These include grained marble and quartzite, and slate - gneiss and schist.
Properties of natural stones
Whatever the origin of the stone, it will be evaluated by specialists according to a certain scale of criteria. They should be taken into account so as not to be disappointed over time, because stone cladding is for the long term.
- The decorative effect of stone
- The aesthetic appeal of natural stone, primarily its color and pattern. The most "inexpressive" stone can be made more decorative by machining.
- Strength of stone
The property which gives the material its durability. Depending on the hardness of the minerals that make up their composition, the stones are divided into three groups:
- hard — granite, gabbro, quartzite, quartz sandstone;
- of medium durability — marble, travertine, limestone;
- low-strength limestones, tuffs.
- Stone Wearability
Wear of stone cover at a human traffic intensity of 1 million people/year.
- Groups of stones by wearability
- Quartzites and rocks of granite group — less than 0.12 mm
- Basalts, microcrystalline marble — 0,12–0,35 mm
- Mild basalts, marble, sandstones, dolomites — 0,35–0,6 mm
- Marbleized limestone, travertine, limestone, tuffs — 0,6–1,5 mm
- Loose limestones — 1,5–2,5 mm
- Stone density
- Depends on the rock's porosity and its constituent minerals. Stones are divided into two categories: light (up to 2200 kg/m3) and heavy (more than 2200 kg/m3), depending on their density, the weight of the piece: the higher the density, the heavier it is.
- Stone Porosity
- The presence in a rock of pores, cracks, caverns and other cavities which directly affect water absorption capacity, the salt- and acid-resistance of the material, which affects its durability, as well as its strength, thermal conductivity, polishability and workability. As total porosity increases, the strength and weight of the stone decrease, but the workability is improved.
- The polishability of the stone.
The ultimate luster of a material is also a property that depends on its porosity. Each rock and material has a limit luster, after which the quality of polished texture is no longer improved. The luster limit of glass is taken as the standard of 200 units.
- Excellent (170-200) units. - full-crystalline marble, fine-grained granite, quartzite;
- good (140-170) units. - granites, marbleized limestones;
- medium (70-140) units. - basalts, limestones, dolomites;
- bad (less than 70 units) - tuffs, loose limestone.
- Water absorption of stone
- Water absorption also depends on the porosity of the stone: the more natural cavities and cracks there are, the more water infiltrates into the material. When water freezes, it increases in volume and exerts a strong pressure in the pores. In addition, after evaporation it leaves concentrated salt solutions from which crystals grow, creating a strong crystallization pressure. At low porosity and high water absorption this pressure creates cracks in the stone. A highly porous rock distributes the crystallization pressure evenly and no new cracks are formed (limestone is a perfect example). The acid-, salt- and frost-resistance of a stone depends on its water absorption and mineral composition.
- Acid resistance of stone
- The property of rocks and materials to react with various acids which can break down or transform the rock. For example, marble reacts to all acids, including food acids (citric and acetic); travertines, limestone, dolomites, as well as marble, are destroyed by hydrochloric acid (it is not found free in nature, but the risk factor increases significantly in cities where chlorides are used for snow removal). But limestone and travertine have a high salt resistance, which means they are good for finishing the basement, interacting with surface waters, carrying salts. Granite also has this property, but the movement of salts can then go along the seams of masonry.
- Frost resistance of stone
- The ability of water-saturated stone to withstand repeated alternate freezing and thawing without showing signs of destruction or significant loss of strength.
Water absorption, salt-, acid- and frost-resistance are the qualities that determine the operational properties of natural stone finishes. They first of all it is necessary to estimate at a choice of a material for an external facing.