ТОП 10:

Read Text 11A and find out the answers to the true/false statements. Discuss your answers in pairs.


Bricklaying and Concrete Blocks

When a wall is built of bricks, the bricks are set in mortar. Mortar consists of a mixture of sand and either lime or Portland cement or, more often, a mixture of the two. Enough water is used in mixing the mortar to produce a paste in which the bricks can be firmly bedded. The bricks must be carefully arranged, or bonded as it is called, in the wall in order to produce a structure of good strength and appearance, the pattern of the brickwork depending on the bond which is used. The pointing or finishing of


mortar joints is also given careful attention since it affects the appearance and the weather resist­ance of the wall.

A mason laying mortar on top of a finished course of blocks, prior to placing the next course.

Each layer of bricks is called a course and the bricklayer has to be very skillful to keep the courses exactly level and the thickness of mortar between each course of bricks the same throughout the length and depth of the wall. The corners of the walls must be absolutely upright.

Nowadays the outer walls of buildings often consist of an outer and inner wall with a space of about 5 centimetres between them, the two layers being held together at intervals by small metal ties. These cavity walls, as they are called, help moisture evaporate better than solid walls. A layer of insulating material is often put in the space between the walls to prevent heat escaping from the building. This is known as cavity wall insulation.

When bricks are built in curves, as in arches or curved walls, the bricklayer has to shape the bricks in order to fit them together. Sometimes quite soft bricks called rubbers are used; these can be rubbed on a hard stone in order to shape them so accurately that they can be built with thin mortar joints. Work of this type is known as gauged brickwork and demands great skill.

Blocks of cinder concrete, ordinary concrete, or hollow tile are generically known as concrete masonry units. They are usually much larger than ordinary bricks and so are much faster to lay for a wall of a given size. Furthermore, cinder and concrete blocks typically have much lower water absorption rates than brick. They are often used as the structural core for veneered brick masonry, or are used alone for the walls of factories, garages and other industrial style buildings where such appearance is acceptable or desirable. Such blocks often receive a stucco surface for decoration. Surface-

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bonding cement, which contains synthetic fibers for reinforcement, is sometimes used in this application and can impart extra strength to a wall. Surface-bonding cement is often pre-coloured and can be stained or painted thus resulting in a finished stucco-like surface. The primary structural advantage of concrete blocks in comparison to smaller clay-based bricks is that a concrete masonry unit wall can be reinforced by filling the block voids with concrete with or without steel rebar. Generally, certain voids are designated for filling and reinforcement, particularly at corners, wall-ends, and openings while other voids are left empty. This increases wall strength and stability more economically than filling and reinforcing all voids. Steel reinforcement can be embedded in horizontal mortar joints of concrete block walls. The introduction of steel reinforcement generally results in a concrete masonry unit wall having much greater lateral and tensile strength than unreinforced walls. Some concrete blocks are coloured, and some employ a split face, a technique that results in two blocks being manufactured as one unit and later split into two. This gives the blocks a rough face replicating the appearance of natural, quarried stone, such as brownstone. For applications such as roadway sound control walls, the face patterns may be complex and even artistic.

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