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BRICKS & BLOCKS

Bricks and blocks are the most basic building components utilized in the construction of any structure. Bricks have changed in shape and size over centuries. There are many different types available; not only in size but also colour, texture and strength. Bricks can be divided into two distinct categories, being; Clay and Concrete (concrete bricks are sometimes incorrectly referred to as cement bricks).

Clay Bricks are manufactured from a mixture of Clay (different clays produce the different colours) and other additives, which are mixed together to make a pliable type mixture almost like plasticine, which is then extruded and cut to size. Concrete bricks and blocks are manufactured from various types of aggregate (sand and other materials like ash mixed with small stone particles) creating the texture and colour, mixed with cement and water, which is then vibrated into a mould creating the shape and size and profile of the brick/block.

Clay Bricks
In the construction of a typical residential house, the cost of clay bricks or clay plaster bricks would generally amount to between 6% and 8% of the total construction cost of the house. In the case of commercial projects, like factories or office blocks, the cost of face bricks and plaster bricks is between 2% and 3% of the total construction cost.

Brickwork being the most visible component of a building often leads to the perception that the vast majority of the cost of the building must therefore be in the brickwork. Fortunately this is not true and should allow one the flexibility of creating different details that can be achieved using Clay bricks in many different ways and applications.

Some traditional advantages of using Clay bricks:
Clay bricks keep interiors comfortable; Heavyweight clay bricks have an inbuilt ability to keep buildings cool in summer and warm in winter. During the day, clay brick slowly absorbs and stores heat thus helping to keep buildings cool. During the night, the stored heat is slowly released and this assists in maintaining the inside temperature at a consistent level thereby minimizing the need for heating and cooling and associated energy costs, which has become increasingly important in a new era.

Clay bricks are fire resistant; because they are fi red at high temperatures during manufacture and are therefore almost incombustible. A clay brickwall is resistant to fi re and collapse. Walls built with quality clay bricks which are properly constructed will produce strong, stable and durable buildings. Clay bricks built in the form of solid or cavity walls offer excellent insulation properties.

Concrete Bricks & Blocks
Concrete masonry has a surprisingly long history and was fi rst seen in Britain in 1840, in the USA it has been in use since 1900. More concrete masonry is used in the USA, Germany and France than any other type of masonry, and in the USA, it accounts for 80% of all masonry used. Although concrete masonry units have been used in South Africa since the early 1900s, their use was initially confi ned to rural areas. Their application increased rapidly after World War 2, due to an increased demand for housing. And this period saw the introduction of mobile block-making machines, where concrete masonry units were produced on site.

The difference between a brick and a block is a matter of size, not material. A block is a masonry unit varying in length from 300mm to 650mm, a brick varies in length from 190mm to 220mm.

Standard specification:
The standard for concrete masonry units is SANS 1215. This standard covers the physical requirements and the sampling of units for testing. Assurance of compliance with the quality requirements of this standard is by obtaining the SABS Certification Mark that the concrete masonry units manufactured comply with the requirements of SANS 1215. This certificate will indicate to purchasers that the concrete masonry units are produced under acceptable controlled conditions with appropriate materials. SABS accredited laboratories are permitted to perform the appropriate testing requirements on behalf of SABS in the awarding of the mark.

Physical conditions and format
Dimensions of concrete masonry units do not appear in SANS 1215, amendment No. 2 but in Appendix F recommended nominal dimensions of concrete masonry units. The use of modular size masonry units is essential if buildings are designed to the 100mm standard module – as stated in SANS 993 modular co-ordination in building. Modular planning is based on a nominal joint thickness of 10mm. Modular wall thicknesses are 90,140 and 190mm.

The permissible thickness of masonry walls in building is 90, 110, 140, 190, and 230 mm and the modular dimensions are 90,140, and 190 mm. In the market place there is a proliferation of different sizes of masonry units. Mainly these are based on the “imperial” brick size of 222 x 106 x 73mm, or multiples of this size up to block size units of 448 x 224 x 224mm. The width of these units exceeds the requirements of SANS 10400, namely 106 and 224mm wall thickness as compared to the “deemed to satisfy” thicknesses of 90 and 190mm.

Thus for commercial reasons, units of reduced width are being made which are non-modular and non-imperial, such as 222 x 90 x 73mm that satisfy the minimum requirements of SANS 10400. Non-modular sizes of units are found in practice not to bond well without considerable cutting of the units. English or Flemish bond and construction of square brick piers is not possible as such units deviate from the basic principle of masonry bonding where the length of a unit should be twice its width plus the thickness of the bedding or perpendicular joint.

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