Clay bricks that are selected or produced for their durability and uniformity of size and shape.
Clay bricks suitable for general building work that is to be plastered.
Clay bricks that are selected or produced for their durability and high degree of uniformity of size, shape and colour.
Clay bricks suitable for use, plastered or unplastered, for general building work below damp-proof course or under damp conditions or below ground level where durability rather than aesthetics is the criterion for selection.
Clay bricks that are selected or produced for their durability and aesthetic effect deriving from non-uniformity of size, shape or colour.
Any class masonry unit produced for structural or load-bearing purposes in face or non-face work, where the manufacturer supplies clay bricks to an agreed compressive strength. An engineering unit is designated by the addition of the letter E followed by a number equal to the nominal compressive strength in megapascals.
Clay pavers that are selected or produced for their durability and for a high degree of uniformity in size and shape, and that have dimensions such that the ration of work size length to work size width is approximately 1:1 , 2:1 or 3:1.
Clay pavers that are selected or produced for their durability and for their uniformity in size and shape.
Clay materials are compounds of alumina, silica with minor amounts of time, magnesia, soda or potash. Iron compounds, usually the oxides, hydroxides or carbonates, are nearly always present as impurities in brick clays, and they account for most of the wide range of colours found in the finished product. Clays containing up to 3% of iron oxide give white to cream or buff colours, which change to pinks and reds as the iron oxide content rises to between 9 and 10%. By adding manganese dioxide in proportions form 1 to 4%, a range of grey and brown colours can be produced.
More important than their chemical composition are the facts that:
- when mixed with water, the clay minerals give a plastic mass that can be shaped by pressure to form a brick;
- at economically practical temperatures ranging between 1 000' to 1 200'C, the clay particles can be fused into a cohesive mass of great compressive strength;
controlled evaporation of the free water surrounding the particles in plastic clay minimises excessive shrinkage and defects in the structure of the brick.
Modern brick manufacture involves high speed processing at extrusion rates of up to 25 000 bricks per hour. Solid bricks of the size traditional in South Africa (222 x 106 x 73 mm) weigh 3 kg to 3.5 kg. Therefore, 1 0000 finished bricks weigh approximately 3,5 tonnes. In the wet state before firing, the clay is heavier. For every 1 000 bricks at least 4 tonnes of material must be dried, fired to a temperature of 1 000' to 1200'C (depending on the clay used) and cooled down.
A wide range of bricks is available in this country. Bricks vary in compressive strength due to the differing qualities of raw material and the method of firing. The compressive strengths can range from 3,5MPa for NFP, to greater than 50MPa for face brick extra and engineering products.
Standard testing is carried out on a sample of 12, to prescribed procedures. Local manufacturers should be able to meet specific needs.
Modern methods of manufacture produce bricks with consistent qualities, but bricks are made from naturally occurring materials and the compressive strength of individual bricks in a given batch inevitably varies.
Note: The compressive strength of clay bricks is not always indicative of their durability.
Clay products for load-bearing designs can be provided to suitable close tolerances and strength.
Efflorescence is the crystallization of salts on or near the surface of brickwork that results from the evaporation of water carrying salts through or from the brickwork. Efflorescence can be no more than an unsightly deposit on newly laid brickwork that soon disappears or it can be serious, causing unsightly permanent discolouration or even the failure of plaster, paintwork or face finishes.
This is often caused by poor waterproofing or detailing. SABS 227 describes degrees of efflorescence and the limits of efflorescence caused by salts in the clay bricks during manufacturing.
Degree of efflorescence:
- Nil: no perceptible deposit of salts;
- Slight: a very thin deposit of salts, just perceptible, or a small quantity of salts occurring only on the edges of a unit;
- Moderate: a deposit heavier than "slight', but that has not caused powdering or flaking of the surface;
- Heavy: a thick deposit of salts covering a large area of the unit, but that has not caused powdering or flaking of the surface; and
- Serious: a deposit of salts that has caused powdering or flaking of the surface.
CLEANING OF CLAY BRICKWORK
1. GENERAL PRECAUTIONS
Staining can mar the appearance of brickwork, but incorrect cleaning techniques can cause permanent damage. Consequently, any proposed method of cleaning should be tried out in a small unobtrusive area and left for at least a week to judge the results before the whole job is tackled. The techniques given here are intended for do-it-yourself work in removing relatively small areas of staining. A specialist contractor should be engaged for cleaning large areas of brickwork.
It is preferable to use wooden scrapers and stiff fibre brushes to avoid damaging the bricks but where chemicals are to be used, the brickwork should be thoroughly wetted with clean water to prevent it absorbing the chemicals, and rinsed thoroughly with clean water afterwards. Adjacent features such as metal windows and the area at the foot of the wall should be protected from splashing of the chemicals.
Many of the chemicals recommended are caustic, acidic or poisonous, so care should be taken and protective clothing and goggles should be worn. Volatile solvents should only be used indoors under conditions of good ventilation. It is essential to identify the type of stain or deposit before any cleaning operations are undertaken.
Remember to thoroughly wet the brickwork with clean water before applying any chemical, and wash down the clean water afterwards.
Bricklaying should be managed carefully to prevent unsightly staining form mortar.
3. MORTAR AND MORTAR SMEAR
Where possible, remove larger pieces with a scraper, then wash down with a dilute solution of a proprietary acid cleaner. The manufacturer's instructions must be strictly followed.
- Wet the brickwork thoroughly with water.
- Remove mortar with a proprietary acid cleaner.
- Remove any residual acid in the brickwork by washing down with water.
When removing mortar smear from brickwork that has a potential to exhibit vanadium staining, the following final procedure is then recommended:
- Treat Brickwork with a 15 - 20% solution of Potassium Hydroxide to prevent the recurrence of the vanadium stain.
Note: Light coloured face bricks are particularly susceptible to severe staining if to harsh an acid is used - please consult your brick manufacturer or Clay Brick Association.