V. E. Translate the following word combinations:

for structural purposes, the most ancient structural material, certain disadvantages, unsuitable for fire-proof buildings, be characteristic of many properties, mechanical strength, sound and heat insulation, owing to its high building qualities, be employed as aggregates, steps of buildings, for facing of fronts, interiors of buildings, the production of artificial building materials, paving materials, artificial stones, clay products, a mixture of cement and crushed stone, come into general use, the development of industry, be divided into three main groups, use main building materials, binding materials, use secondary or auxiliary materials, the interior parts of the buildings, for bearing structures, for joining different planes, the interior finish of the buildings, utilize various artificial stone materials, silica brick, light concrete

VI. A. Read the text and speak on building materials

Materials that are used for structural purposes should be hard, durable, fire-resistant and easily fastened together. Natural building materials are: stone, sand, lime, clay and timber.

Wood is the most ancient structural material. It is light, cheap and easy to work. But wood has certain disadvantages: it burns and decays and is therefore unsuitable for fire-proof buildings.

Stone belongs to one of the oldest building materials used by man. It is characteristic of many properties: mechanical strength, compactness, porosity, sound and heat insulation and fire-resistance. Owing to its high building qualities natural stone is widely employed in modern building for foundations, walls and steps of buildings; for facing of fronts and interiors of buildings.

Gravel and sand are widely employed as aggregates in the production of artificial building materials and as paving materials. Rocks are employed in the production of building materials, for instance, Portland cement, lime, building gypsum, brick and artificial stone, etc.

Cement, bricks, clay products and concrete are examples of artificial building materials. Bricks were known many thousands of years ago. Concrete is a mixture of cement, sand, crushed stone and water. Steel has come into general use with the development of industry.

All building materials are divided into three main groups: 1. Main building materials such as rocks and artificial stones, timber and metals. 2. Binding materials such as lime, gypsum and cement. 3. Secondary or auxiliary materials which are used for the interior parts of the buildings. We use main building materials for bearing structures. Binding materials are used for making artificial stones and for joining different planes. For the interior finish of the buildings we use secondary materials.

At the end of the 19^th and the beginning of the 20^th centuries people began to utilize various artificial stone materials such as silica brick, light concrete and others.