Stone

Nowadays stones are a very common building material that was used by construction field. Stone play an important role due to their hardness, durability, environmentally friendly and nature good looking. You can design the shape of the stone as you like. We always found stone at anywhere, for example your own house, floor, roof, wall, garden and so on.

In geology, stone is a naturally occurring solid aggregate of minerals or mineraloids. Stone are also known to geologists as rocks. The Earth's outer solid layer, the lithosphere, is made of rock.

Stones can be classified into two:

- artificial stone

- natural stone

 

Artificial stone (engineer stone)

This stone is made by crushing and grinding natural stone and then re-constituting it in a mould with cement mortar. The cement (binding particles) can be colored by adding inorganic dyes (pigments) match the color of the stones.  It is made more uniform and affordable than natural stone and has a high quality and durable psychical property which is stronger than most natural cut stones used in buildings and more resistant against acid and alkali attacks.

 Different types of artificial stones

Nowadays, with the help of concrete it is practically quite possible to duplicate the natural stone of any kind, color and dimensions. At the same time, the artificial analogue is, at least, two times cheaper than the natural sandstone, limestone or quarry stone. Besides, a number of problems may be solved, if it is used for decorating of interior and exterior wall surfaces. Just try to assume, how much will it take you to select the required stones to be alike by its color and texture? And what do you say about its dressing? Quite the contrary, the artificial slabs are manufactured on the production lines and can be made of the required kind and dimension. At the same time, unlike to the natural stone properties, which texture quality depends on weather conditions, the slab surface has rather a rich color that can be gained by a number of coloring agents. The products can be made along with a finished combination of stones imitating a certain style of stonework. In a short space of time, you are able to change a certain house wall for some fragment of the medieval castle. 

There between the natural stone and its artificial analogue is a big difference that involves a quantity of man-hours spent on their laying out. If in the first case laying needs special skills, than in the second case only the producer’s instructions and recommendations shall be followed. The artificial stone is featured with a number of physical and engineering properties. It is stronger and more durable than its natural analogues (e.g. limestone and sandstone). In spite of the fact that the last ones are good-looking they are prone to breaking at their splits and they are fast at failing under influence of water and wind. Their concrete twins have no similar problems. Certainly, by its strength the artificial stone cannot come up with such a monumental matter as granite. But do not forget that the granite inhabits some background radiation to be not found in the concrete products. Since the materials of low volume weight are used as aggregates, the artificial stone is quite easier than its natural analogues. That means that while conditioning your house with the artificial stone you do not need to build the wall foundation embedded elements to make the bed heavier. That is why you do not need to fear for sinking of your building and no cracks and tilts can occur in your structures. The next thing: the concrete product is of monolithic type and therefore no defects can occur inside it, but not as for the natural stone. Regardless of the methods of stone mining (in foreign countries they usually cut rocks, but in Russia the rocks are blown out) some cavities, cracks and other defects may be found inside the stone. These defects are able to affect any wall facing. In addition to, if air cavities are absent, high frost-resistance of the artificial stone is gained. 

The artificial stone consists of the main aggregates treated from natural rocks. The sand is a fragment of rocks being split under influence of wind. The cement is a former dolomite treated by means of hydration, milling and firing. In addition to, after contact with water the very binding agent transforms to the so-called “cement stone”. The coloring agents consist of metal oxides and dioxides listed among main constituents of any minerals. Among the artificial stone components the plasticizers of different features are used. For example, one grade of the plasticizers is able to decrease the rate of concrete water (the less content of water, the more plastic concrete), other ones are able to protect against forming of air cavities and the third ones can decrease the rate of abrasiveness. A number of the plasticizers are of natural origin. For instance, the haydite (it makes the product light in weight) is made of the fired and expanded clay. To improve material strength and moisture resistance properties some manufactures prefer to add in the mixture some amount of fiber. If, as a result of wrong laying or in a case of exposure to precipitations the stone splits, the applied fiber will retain it against breakout. The composition may be mixed with gypsum that is able to makes it cure in a short time. However, this type of stone is good enough only for interior surfacing. As a rule, all the additives are original elements. Thus, they do not influence the product ecological condition. But nevertheless, some artificial components are also used. Instead of the cement some acrylic and urea resins, organic concrete and other polymers may be used as binding agents. See binder composition characteristics in the product sanitary certificate.

Method of Manufacturing

The composition of cement (or other binding agent), coloring agents and other additives is filled in a special mold or compressed in it. The mixture is rammed down, cured and then dried down. Only the product, being completely dried up, can be used for facing of interior or exterior elements. Only one side of the slab is patterned – the other side (used for laying) is completely flat. Depending on the imitating stone properties the molds may be rigid (plastic and gypsum ones) and smooth (polyurethane ones). For example, the stuff texture to be similar to the natural stone’s (featured with negative angles) may be gained only by means of the smooth mold. The concrete product properties directly depend on quantity of the molds used for filling. Large companies usually use quite a great number of different molds thanks to that repeatability of a certain pattern in a single lot can be hardly seen. It is worth noticing that depending on the product lot the artificial stone colors may vary. But nevertheless, it additionally proves that our stone has unique properties.

Color fastness is one of the properties that the artificial stone is featured (certainly, if manufacture uses high-grade coloring agents). The concrete is made of colored aggregates and, therefore, after a number of years it does not loose its coloring properties and does need additional make-up. Even factory paving slabs are able to retain their coloring. However, if the slabs are made with only their surface colored, their appearance will deteriorate after a time. As it is well known, water has a tendency to sharpen any type of stone. And the artificial stone cannot be considered as an exception. But if the water absorption property is within norm (3 to 8%), the stone retains its mechanical properties. Laying the artificial stones where contact with water can take place is not recommended.

Special water-repelling admixtures reduce water negative influence. Such admixture can be used for treating of any surfaces. It coats the surface of a stone with elastic semi-impermeable membrane that protects it against influence of not only the water, but also of high temperature, solar radiation and acid rain. Considering our environment, when winter temperature varies from - 10 to + 5 °C, the facing material should have cold-weather properties. 

If the product is made of high-grade material, no temperature variations can affect it. Depending on the manufacturer and on the rate of frost-resistance the product can be affected by 100 – 200 cycles (by GOST 70 cycles is enough). The cycle can look as follows: the stone having been frozen in the lab environment down to -15 or - 20 °C is defrosted for 4 hours up to the temperature of +2 °C. Before freezing the stone is kept in water for 4 hours. 

Of course, in natural environment the stone can hardly find itself in such condition. But nevertheless, it is considered that the stone is influenced by 4-5 cycles. Also, average density of the product is of great importance (the less density, the lighter stone). Even relatively weak bearing structures are able to sustain it. In addition to, low average density is the very property to be important for laying the product. Compression strength is significant property required when paving artificial stone slabs and, therefore, the lasts are able to bear any weight without deformation. 

The rate of concrete stone strength may be characterized by the following example: one square centimeter of the slab used for paving of 4 cm garden path or ground is able to bear the weight of 500 kg. But it is worth noting that the facing slabs cannot be used for paving. Another nuance: when the artificial stone is heated it neither burns, nor exhales smoke or harmful substances. Therefore, it is the best one to be used for facing of fireplaces. But do not use the artificial stone for facing of the elements exposed to extremely high temperatures.

The following video shows how to make artificial stone.

Range of Application

As the material is applied both for interior and exterior surfacing, all depends on your local environment. The stone can be used for decorating of the reception-room, kitchen, home theatre, indoor pool and fireplace, as well as it can be used for surfacing of the door openings and ornamental columns. The stone is perfect for laying on the facade, pedestal, roof, chimneys and vent ducts, windows, balustrades, balcony banisters, staircases and steps. The barrier and supporting walls, angle dummy joints, decorative blocks and booms may be surfaced with the stone as well. No restriction of concrete use (with cement binders) is stipulated in SNiPs as the very material does not emit toxins, formaldehydes and other danger substances. If the premises worked with stone are quite cold for living, you may use the heat floor systems that are offered in the market in great variety. Any possible restrictions may rather depend on your tastes and attitude to comfort. It is just a few steps may be done to change a spacious room for a stony “crypt”. The artificial stone may be used around your house area. The summerhouses, halls, columns, fountains, benches, sculptures and other architectural elements of the classic garden will help you to change your landscape. The decorative pools, pavements and paths, curbs, posts, fences, vegetable gardens, gates etc may be added to the above list. Now, the most popular product is the slab imitating wooden saw-cuts and boards. Really, the natural wood elements can perfectly look at any landscape. No doubt can be made about material condition. Unlike to the wood subject to decay, the concrete has a long life. A decorative thin-walled brick made of concrete may be considered as the other invention that can add some new features. The artificial stone can perfectly match widely distributed country architectural elements: wooden and plastered walls, forging fences, gates, staircase and balcony railing, natural and smooth tiling roofs, modeling and mosaic, grates and lamps taken to the façade and large dimension natural stones. The one thing should be followed – selection of proper color and texture of the stone and harmony of architectural elements. It is worth noting that nowadays the artificial stone is widely used for exterior and interior surfacing of not only private buildings, but also public ones – cafés, restaurants, clubs, supermarkets, hotels and banks. A number of exclusive stylistic facilities may be applied. On the one hand, the concrete stone imitating the natural analogue is the very personification of any tradition. On the other hand, the artificial stone columns or slabs with roughly worked stone design are the perfect ones to match the interior made in the style of minimalism or hi-tech. Besides, the artificial stone can be use for reconditioning of the old building appearance. Quite often, monuments of architecture or natural stone damaged elements are the ones that can be reconditioned by means of the artificial stone, as no substitution can be seen.

Natural stone

The most common natural stones are marble, granite, travertine, limestone, slate, sandstone and quartzite. One of the best qualities of natural stones is that no two stones are alike. Because stone is made in nature, its colors vary, making it more beautiful. When considering using natural stones in your house or in a project, you will want to consider their properties to determine which natural stone is best for the job.

1.   Mechanical Properties

o   One of the important properties of natural stone is its place on the Mohs hardness scale. The Mohs hardness ranks natural stones on a scale from 1 to 10. If a stone is a 1, it is one of the softest; 10 is the hardest. According to the Granite Land website, the harder the stone is, the less likely it is to be scratched. Limestone measures 3 on the Mohs scale; granite, 6.5; and quartzite, 7.

Young's modulus is another important property of natural stone, because it measures the elasticity of the stones. It measures the amount of stress that can be put on the stone before it deforms. It is measured in gigapascals (GPa). According to the Granite Land website, the majority of natural stones measures about 50 GPa.

2.   Thermal Properties

o   One thermal property of natural stones is the co-efficient of thermal expansion. When a natural stone is exposed to a distinct temperature increase, it causes the stone to expand at a specific rate. The co-efficient of thermal expansion for natural stones varies. For example, the co-efficient of thermal expansion for quartzite is 1.3, while granite has 7.9 and limestone, 8.0.

Specific heat capacity is another thermal property that tends to be important for natural stones. The specific heat capacity is the amount of thermal energy required to raise the temperature by 1 degree C per unit mass.

 
 3.    Chemical Properties

 o  Acid resistance is important for natural stones. It imparts how much weight of the natural stone will be lost when the stone sits in an acid for a specific amount of time at certain temperatures. Granite is hard and brittle. It can easily withstand acids. On the other hand, marble can be easily corroded by acids.

Natural stones do absorb liquid, but each stone has different chemical water absorption properties. The water absorption of different natural stones is measured by a percentage point. It measures how much weight is increased after the stone was submerged in water at a defined temperature for a specific amount of time. The typical water absorption of granite is .3 percent, while the absorption of marble is .1 to .2 percent.

Basically natural stone can be found at anywhere around the world. Each natural stone have their own uniqueness and so they also have their own properties too. It is obtained from the earth and cutting it to the sizes and shapes for construction usage. There are three types of natural stone:

1. Igneuos stone - Hard and non-porous rock formed from the slow or quick cooling of molten magma. The best example is granite.

 
Granite

Properties:-
      - High compressive strength
      - Hardness and durability is strong
      - Less porosity
      - High themal stability







Granite is a popular floor, wall and countertop covering for all areas of the home. Used in building for centuries, granite's hard, durable nature makes it the perfect building material for interiors and exteriors alike. Not all granites are created equal and not all stones that are labeled granite are in fact granite. Most stones labeled and sold as granite do have many of the same characteristics and maintenance needs.

Surface Finished of Granite

Granite is extremely hard and durable and can be ground to a high polish. The stone can also be ground without being polished, resulting a more muted, matte finish. This process, known as honing, often exposes small fissures, holes and other marks within the stone, as a high polish will reflect light off these marks, deflecting the eye, while honing will reveal them.

Applying heat to granite and brushing its surface in a process known as "flaming" or "brushing" will result in the weaker surface particles being removed. The result is a textured, rough surface made up of only the strongest minerals of the granite remaining.

Any granite can be polished, honed or flamed, although not all will be offered this way by any one manufacturer.

Caring for Granite

Since granite, like all natural stones, is porous, it should be taken care of properly. Acids such as lemon juice, tomato sauce or vinegar can strip the finish off of the stone by removing the weaker particles from its surface. This is known as etching, and will result in a polished stone appearing dull.

To prevent this process from happening and to prevent stains from the stone absorbing oils and greases, granite should be cared for with stone treatment products. These include special stone cleaners that contain no acids or alkalines and sealers which penetrate the stone, filling its pores so that no other material can be absorbed.

Stone cleaners or mild detergents work well to clean granite, and granite requires sealing whenever water ceases to bead up off its surface.

Uses of Granite

While one of the most common uses of granite in the home is the kitchen countertop, granite can be used in multiple other ways. Granite is often installed as a tabletop or as floor tiles.

Granite tiles can also be used on the walls of backsplashes in the kitchen or on the walls of a shower. Some granites, such as Blue Macuba, a rare blue stone, are available in mosaic form. These work as accents with other tiles in borders, or as tiles cut into the corners of larger tiles.

Example: granite flooring, it gives more attractiveness to the Interior. 

 Granite flooring

2. Sedimentary stone - Soft and fairly porous rock fromed from deposits of eroded pre-existing rock that settled in layers mostly on sea beds, and became compacted. The best examples are sandstone and limestone.

Limestone

Properties:-

    - Porous

    - Very widely and hardness

    - Soluble in water containing carbon

      dioxide

    - Attacked by acid

    - Use as raw materials and manufacture

      cement

Limestone is calcareous sedimentary rocks formed at the bottom of lakes and seas with the accumulation of shells, bones and other calcium rich goods. It is composed of calcite (CaCO3). The organic matter upon which it settles in lakes or seas, are preserved as fossils. Over thousands and millions of years, layer after layer is built up adding weight. The heat and pressure causes chemical reaction at the bottom and the sediments turn into solid stone, the limestone.

The rock which contain more than 95% of calcium carbonate is known as high-calcium limestone. Recrystallised limestone takes good polish and is usually used as decorative and building stone.

A part of calcium molecules if being replaced by magnesium, it is known as magnesium lime stone or dolomite limestone.

Limestone that will take a polish are considered marbles by most people, but technically, if there are still shells visible or the structure is not crystalline, it is still a limestone.

Physical Properties of Limestone

Physically, Limestones are Quite impervious, Hard, Compact, fine to very fine grained calcareous rocks of sedimentary nature.

Hardness	3 to 4 on Moh's Scale
Density	2.5 to 2.7 Kg/cm3
Compressive Strength	60-170 N/mm2
Water Absorption	Less than 1%
Porosity	Quite low
Weather Impact	Resistant

Chemical Properties of Limestone

Chemically, they are calcareous rocks principally of calcic minerals with minor amounts of alumina, ferric & alkaline oxides.

Lime (CaO)	38-42%
Silica (SiO2)	15-18%
Alumina (Al2O3)	3-5%
MgO	0.5 to 3%
FeO + Fe2O3	1-1.5%
Alkalies	1-1.5%
Loss On Ignition (LOI)	30-32%

Note :- Limestone, like marble and other calcareous stones, are referred to as acid sensitive. Calcareous stones are readily dissolved in acid, therefore acidic products should not be used on limestone and marbles.

example of limestone product - limestone wall

3. Metamorphic stone - Hard and nono-porous rock formed from preexisting rock that has been altered by intense heat or pressure. The best examples are marble and slate.

Marble Stone

Properties:-
     - Coarse
     - Denser
     - Less porous
     - Varying colour and vein
     - Very hard and scratch proof
     - Exellent self-polish ability
     - Vulnerable to acid attacks
     - Surface not lasting if used externally
       in a polluted atmosphere 

Marble is metamorphosed limestone, composed of fairly pure calcite (a crystalline form of calcium carbonate, CaCO3). It is extensively used for sculpture, as an building material, and in many other applications.
Faux marble or faux marbling is a wall painting technique that imitates the color patterns of real marble (not to be confused with paper marbling). Marble dust can be combined with cement or synthetic resins to make reconstituted or cultured marble.

Marble is a metamorphic rock resulting from regional or at times contact metamorphism of sedimentary carbonate rocks, either limestone or dolostone. This metamorphic process causes a complete recrystallization of the original rock into an interlocking mosaic of calcite and/or dolomite crystals. The temperatures and pressures necessary to form marble usually destroy any fossils and sedimentary textures present in the original rock.
Pure white marble is the result of metamorphism of very pure limestones. The characteristic swirls and veins of many colored marble varieties are usually due to various mineral impurities such as clay, silt, sand, iron oxides, or chert which were originally present as grains or layers in the limestone. Green coloration is often due to serpentine resulting from originally high magnesium limestone or dolostone with silica impurities. These various impurities have been mobilized and recrystallized by the intense pressure and heat of the metamorphism.