THECNICAL MATERIALS  IV.

NATURAL AND ARTIFICIAL STONE

NATURAL STONE

Natural stone materials are those inorganic materials that are derived of rock or possess a similar quality of rock. These materials are used almost exclusively in the construction sector.

The stones are extracted from quarries manually, mechanically or using explosives. To later use in construction, the stones must be cut for an adequate size and shape (depending on their final use).

Depending on their origin they can be classified into the following types:

- Magmatic or igneous rocks: igneous rocks are formed when the magma cools and solidifies, with or without crystallization. They are compact, hard and very resistant. An example is granite.

- Sedimentary rocks: sedimentary rocks are rocks formed by the accumulation of sediments. They are easily found in nature and cheap, such as limestone.

- Metamorphic rocks: metamorphic rocks are rocks formed by pressure and high temperatures. They can be separated easily into flakes and are rarely used, except marble and slate.

They have been used in construction since ancient times, due to its low cost and abundance.

Concerning mechanical properties, (in general) they are heavy, shock-resistant and difficult to work. They are impermeble and require a binder to be joined.

Granite	Limestone	Marble	Slate

ARTIFICIAL STONE

They are classified into different groups, according to their composition

1. CEMENT AND  DERIVATES

Cement is a binder formed from a mixture of limestone and clay calcined and then crushed, which has the property of hardening on contact with water. Mixed with gravel, sand and water, it creates a uniform, malleable and plastic mixture which sets and hardens, acquiring a stony consistency, called concrete. Its use is widespread in construction and civil engineering.

It looks like a grey powder like flour.

Concrete properties are very similar to natural stone properties, but with the advantage that we can give it the shape we want because it is generated in a liquid way (pasty) and solidifies into a mold.

Cement	Cement mortar	Concrete

2. CERAMIC MATERIALS

Ceramics (derived from the Greek word "burnt substance") is the art of making objects based in clay and transforming them by heat.

Depending on the quality of the clay and the oven temperature, different qualities of materials are obtained. We classify them from the cheapest ones to the most expensive ones.

Bricks: A brick is a piece of construction, which is ceramic and generally cuboid-shaped, whose dimensions allow it to be placed with one hand by an operator. It is used in construction for indoor and outdoor walls. It is cheap, easy to install and light. They are baked at less than 900 ° C.

Roof tile: The roof tile is a piece to form the roofs of the buildings in order to receive and channel rainwater, snow or hail. The shape of the roof tiles and the materials used can vary; shapes can be regular or irregular, flat or curved. Regarding materials, they can be ceramics (made with clay - the most common), concrete or stone (slate). Water slides easily on them and they prevent leaking. Ceramic tiles are baked at approximately 1000 ° C.

Tiles: The term tile refers to a thin ceramic piece, generally square or rectangular, in which one face is glazed: This is the result of baking enamel on one side; this side becomes waterproof and bright. Tiles are generally used for coating interior or exterior walls. The baking temperature of the tiles must be higher than 900° C.

Pots, pans, etc. They are not used as technical materials because they aren't used in construction. 

Stoneware: Stoneware is the term that designates a ceramic paste, formed by natural clays and other additives such as silica. Its main features are its hardness and being almost waterproof once baked. The baking temperature ranges from 1200° C to 1300° C, depending on their chemical composition. The largest field of application of stoneware is for floor coverings.

Porcelain: Porcelain is a traditionally white, compact, hard and translucent ceramic product. It is obtained from an elaborate paste composed of a very specific type of clay mixed with other materials. The baking process is performed in two stages. The first is obtaining the base (850-900 ° C) and the second corresponds to the glazing (at temperatures which vary depending on the product between 1175 and 1450 ° C). It is not used in construction but to make crockery (dishes).

3. GYPSUM AND DERIVATES

Gypsum is a product prepared from a natural rock. Gypsum is obtained by dehydration of the rock, adding various additives to it and baking it in various stages.

This product has characteristics of fast setting (solidification) and good adhesion that allows us to use it directly once mixed with water. Its properties -which make it useful in buildings- are easy handling, good finish, good price and beautiful white colour. Its main problem is its low resistance to water and wetness.

Gypsum is used mainly to cover the bricks of the walls.

Plaster (escayola) is some purer and better quality gypsum. It is used to make false ceilings and moldings.

Drywall (pladur) is a kind of prefabricated wall consisting of cardboard sheets coated with gypsum, which are placed like pieces of a puzzle and allow the placement of walls to be quick and cheap, although its resistance is lower than that of bricks.

Gypsum	Working with gypsum	Plaster	Drywall

4. ABRASIVE MATERIALS

An abrasive is a substance that acts on other materials to rasp them.

Abrasives, which can be natural or artificial, are classified according to their degree of hardness. They are an agglomerate of grains. The other material is rubbed against them. One example is the grinding wheels, abrasive papers, grindstones knives and discs for grinders.

5. REFRACTORIES

The term refractory refers to the property of certain materials to withstand high temperatures without decomposition. “Refractories” means refractory materials.

Refractory bricks are materials whose base is clay, but it is accompanied by other compounds that make it more resistant to heat, thermal shock and dilation. These compounds vary in proportion and quantity. One widely used is the Wolfram. These materials -due to its composition and the high temperatures necessaries to bake them- are expensive.

The refractory cement is a special type of cement with good thermal properties, and is used for bonding refractory bricks.

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