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2010 CMA AWARD
In 2010 Western Granite was awarded the Regional and National Awards of Excellence by the CMA for their Bloukranz Terrazzo Face Brick used in the Cape Town International Car Rental Facility.
CMA AWARD
In 2008 Western Granite received two regional Awards of Excellence from the CMA for the category Masonry Vintage for the Islamia College in Rondebosch East and for the category Masonry Industrial for Platinum Park, Milnerton.
Calcium silicate terrazzo paver
In 2009, Western Granite launched its latest product range, the calcium silicate terrazzo paver. The paver has already been used in the revamp of Cape Town International Airport and has been extensively used in the Cape Town urban regeneration project, most notably on the Cape Town Station forecourt and Cape Town Civic Centre.
Green Building
Western Granite Bricks is a supporter of and firm believer in the sustainable building movement and in line with this became a full member of the Green Building Council of South Africa in March 2009.
Terrazzo face brick
In 2009 Western Granite launched a new product, the terrazzo face brick. This face brick has already been used in the new International Car Rental facility at Cape Town International airport and in the construction of a school in Vredenburg.

Comparison of calcium silicate, concrete and clay bricks


Background

Clay bricks have been in use for more than a thousand years and so they are well known compared to concrete, that has been around for only 200 years and calcium silicate about 150 years. In South Africa, prior to 1970, concrete products constituted less than 2% of the masonry market and calcium silicate was unknown.

30 years later, thanks to a concerted marketing campaign by the CMA, concrete masonry claims 60% of buildings built in the Cape. The industry has rapidly adjusted to it's use. Notwithstanding, there still are those that prefer clay to concrete claiming that concrete exhibits poor resistance to damp, looks and is cold and cracks more than clay brick walls do.

The fact is, concrete bricks are different to clay and if used incorrectly will exhibit some of these nasty characteristics. Technically the products are quite different.

Manufacturing process

Clay bricks are made in a process that starts with a suitable blend of clays that have to be mined, aged, then milled/mixed to even consistency. The clay is then extruded through a special press and sliced to size. These unburnt bricks are dried out before being placed in a kiln that is heated to between 700c and 1100c. Thereafter, when the firing is complete, the bricks need to be cooled and classified as to colour and strength. The process is very energy intensive, generates large amounts of carbon dioxide, is quite difficult to control and takes up to 3 months to complete. If that was not all, the set-up cost of a reasonable factory is about 10 times that of concrete for the same output.

Concrete bricks are far simpler to manufacture: Suitable sands, stone and cement are proportionately mixed together with water, vibrated in a press, allowed to cure for about 14 – 28 days and are then ready for use. Total process time 15 to 30 days. Energy costs are quite low and there is minimal pollution.

In spite of the disadvantages of the clay brick manufacture cycle the processing cost of concrete and clay is not too different. Clay apparently has one major asset – a very attractive facebrick that concrete struggles to match. The rich colours of yellow, red and plum, glossy finishes and subtle variations are very much appreciated.

Calcium silicate bricks are closely allied to concrete. They too are made from blends of sand and stone with a high silica content, but instead of cement, use lime as the binder. This damp mixture is compacted to the shape of the brick under massive pressure. The brick is then baked at about 200C for 8 hours – known as autoclaving. The lime reacts with the silica in the sand to form a similar binder material to that of cement. The advantages of the calcium silicate brick is that the processing time is only a few days and the brick can be used immediately after autoclaving. Because of the pure white colour of the calcium silicate binder and the bleaching action of the autoclave temperature the bricks are characteristically white. Suitably pigmented, the calcium silicate brick can be made in a unique range of pastel colours. The bricks are very consistent in colour, shape and texture. They are somewhat more expensive to make than concrete products.

Properties in the wall – movement.

Technically clay and concrete products have different properties that affect the way they should be built into a wall. Clay bricks tend to expand after manufacture in the first few years of their life – about 3mm to 5mm over 10 metres of wall length. So expansion joints need to be provided. Concrete bricks on the other hand tend to shrink about the same amount (partly curing and partly drying out) usually in the first 6 months after construction. So concrete masonry walls need contraction joints. Both of these opposite movements require joints roughly every 5 to 6 metres otherwise cracks will appear. Calcium silicate bricks also shrink due to drying out, but only about half that of concrete brick walls

Moisture absorption

Contrary to common belief concrete bricks have relatively low moisture absorption – about 5% to 7%, whereas clay bricks are very variable, depending on the burning and type of clay, can range from 5% to 20% moisture uptake. The significance of this is that clay bricks need to be wet before laying otherwise they suck the moisture out of the mortar, whereas concrete bricks need to be laid dry. If they are wet they ‘float’ and the mortar does not acquire sufficient early stiffness to keep the wall from sagging out of shape. Calcium silicate bricks have slightly less moisture absorption than concrete and because of their relatively smooth texture need more care in laying.

Thermal

Individually, solid clay bricks have a lower heat transfer (better insulation) than concrete bricks. However once they are imbedded in mortar and plaster, the difference is minimal, especially if it is a cavity wall.

Another thermal issue is the retention and release of heat – a heat reservoir. In SA with relatively mild seasons the important comfort factor is the absorption of heat during the day and release at night. Concrete bricks are more effective than clay because they are generally denser and have a higher thermal capacity. The calcium silicate brick is the densest of the three and therefore the most effective.

Dimensional stability

Generally concrete products are true to size and texture whereas clay bricks can vary considerably in size, shape and texture. Thus clay bricks will need a thicker coat of plaster than concrete to obtain an even finish. Once the plasterer has mastered the art of working with lower suction concrete bricks he will be faster and more economical than on clay bricks. Calcium silicate bricks are even more consistent in size, shape and texture and the calcium silicate face brick is therefore easier to lay than the clay face brick.

Painting

Concrete bricks accept paint relatively well whereas clay does not. Clay bricks often exude metallic salts in their early years which causes paint to peel off. The calcium silicate brick is superior in this aspect to both concrete and clay. There are no free salts in the calcium silicate brick and its surface texture and pore structure is relatively fine. It should be noted that the presence of moisture in the brickwork – eg rising damp - will almost certainly cause paint to peel on any brick, clay, concrete or calcium silicate.

Efflorescence

Masonry walls by nature contain lots of free calcium salts from cement that convert to calcium carbonate in the air – a white efflorescence or weeping streak. This is exaggerated if the wall becomes soaked with water. Unplastered clay bricks (non facing) will sometimes exhibit a green stain which is caused by metallic salts washing out. The calcium silicate brick with its very fine pore structure exhibits the least efflorescence

Stength & Durabilty

Building regulations stipulate the same strength of brick, clay, concrete or calcium silicate, for a specific design of a wall. Durability is generally a function of strength. The clay brick by nature of its manufacturing process hardens from the outside inwards. If the outer face is damaged it is possible that the soft inner could deteriorate. Concrete and Calcium Silicate on the other hand tends to have the same strength throughout.

To obtain resistance to weathering clay face bricks need to be greater than 30 Mpa, Calcium silicate 25 Mpa and concrete about 20 Mpa.

Clay bricks can be used around fireplaces as can calcium silicate. Concrete tends to deteriorate at temperatures above 450C.