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  • Writer's pictureBenny Kuriakose

Points to be Considered in the Manufacture of Bricks

Ordinary bricks are the leading construction materials and are among the earliest building materials. It is strong, long-lasting, affordable, and easily accessible. Clay is formed into uniformly sized rectangular blocks, which are then sun-dried and burned to create the bricks. Good bricks have a compact structure and are reasonably free from cracks, lime, stone and pebbles.

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The Process of Manufacturing Bricks

The preparation of clay, moulding, drying, and burning of the bricks are the steps involved in the production of bricks from clay. Brick laying is very simple and the bricks do not require dressing.

The steps involved in the manufacturing of bricks are :

1. Clay Preparation

For the manufacturing of bricks, pure clay is required. The clay is cleared of debris such as stones and plant materials. If there is a significant amount of particulate matter, the clay is washed and screened. The clay lumps are also reduced to powder. The clay is washed and then allowed to air dry to soften it. The exposure time ranges from a few weeks to a full season. After that, any ingredient that has to be added is spread out on top of the loose clay. Water is then added to the clay in order to give it a plastic character to mould it into the shape.

2. Moulding

The moulding technique involves shaping prepared clay into a rectangular form. Depending on the size of the project, there are two methods to go about this procedure.

a) Hand moulding

In hand or manual moulding, the bricks are moulded by hand. It is used in for small-scale brick manufacture. The moulds are rectangular boxes made of wood or steel with top and bottom openings. The clay is forced or pushed into the mould such that it fills all of the mould's corners.

b) Machine moulding

Machines may also be used to perform the moulding. When bricks need to be produced in large quantities, this method is generally preferred.

c) Drying

The bricks still contain some moisture after the moulding process. In order to prevent them from cracking during burning, they must be dried. Natural processes are used to dry the bricks. Drying time might range from three to ten days.

d) Burning

The dried bricks are burnt either in clamps (for small- scale purposes) or kilns (for large scale purposes) to a certain temperature. This phase of brick production is crucial since the bricks will get stronger and harder throughout this time.

Burning occurs at temperatures of 1100 degrees Celsius. They would become fragile and easy to shatter if they burned past this point. If they were burned below this threshold, they wouldn't reach their full potential and may even absorb moisture from the air.

The firing process gives the bricks their characteristic properties. Primitive firing conditions produce an inconsistency that gives an attractive and subtle variation in colour and texture.

Only fully burnt bricks should be used for the construction of buildings. Half-burnt bricks will have only a bit more strength than mud blocks and will not stand up to the weather.

In the case of country burnt bricks, the bricks are not uniformly burnt. While a large proportion is satisfactory, those on the outside are under burnt and those in the heart of the kiln and the fire holes are over burnt. If so, they may be misshaped and cracked owing to the excessive heat. If the bricks are over-burnt to a blackish colour but not to the extent of losing their shape, then they can be used.

Wire Cut Bricks

The clay, which is usually fairly soft and of a fine texture, is extruded as a continuous ribbon and is cut into brick units by tightly stretched wires spaced at a height or depth for the required brick. Allowance is made during the extrusion and cutting for the shrinkage that will occur during firing. Wire cut bricks do not have frogs, and on many of the wire cutting marks may be seen.

Production of brick in large scale.   Image by Egbert in donker Afrika via pxhere
Production of brick in large scale. (Image by Egbert in donker Afrika via Pxhere)

Important Points to Consider in the Selection of Soil for Making Bricks

There are certain aspects that need to be kept in mind while selecting for clay / soil for the preparation of bricks :

  • Good bricks are mainly made from sandy clay. An optimum proportion gives the best quality bricks. If the soil is too clayey, sand will have to be added. If the soil is too sandy, clay will have to be added.

  • Too sandy bricks will give good compressive strength, but their weathering quality is poor. Too clayey means more warping and less strength.

Too much sand content will erode the bricks
Too much sand content will erode the bricks
  • The clay prepared should not contain large aggregates because they would cause splitting and disruption when the clay is fired. In the case of factory-made bricks, the clay is passed through a pug mill to get a more uniform clay.

Large aggregates causing holes in  the brick
Large aggregates causing holes in the brick
  • The soil or the water added to make the bricks must not contain any of the water-soluble salts – e.g., sulphates and chlorides. Also, no salt water should be added in the process of making bricks. Both are detrimental to the durability of the buildings. If they are present, it will lead to the problem of salt crystallisation or efflorescence, which causes serious problems.

Common Manufacturing Defects

The common flaws that happens during the manufacturing are as follows :

a) Cracking and warping of bricks are two of the major defects in bricks. Cracking and warping, which create weaknesses in the bricks, may be due to the following reasons:

  • These may be due to the exposure of green bricks to direct sunlight or rapid drying winds.

  • These may be due to the placing of green bricks into the kiln too soon.

  • These may be due to too low sand content.

b) Too much sand on the other hand produces bricks, which are brittle, and their weathering quality is poor.

c) Bricks, which have a lime content, will swell and burst after firing when the brick is exposed to moisture due to slaking.

d) If the moulds are dipped into water each time to prevent the clay sticking to them, it will also lead to surface cracking. Dipping in sand generally produces better bricks with sharper profiles.

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