Manufacture of Bricks for Masonry Construction

Brick is made from clay or shale. The collection of raw materials to the final molding of the clay to brick involves different stages of the process. The manufacture of brick for masonry construction comprises of 5 major steps:

1. Selection of Site
2. Preparation of Brick Earth
3. Molding of Bricks
4. Drying of Bricks
5. Burning of Bricks

Fig.1. Steps in Manufacture of Brick

We will discuss each step one by one in detail.

1. Selection of Site

The site selected for the manufacture of the brick must involve the following considerations:

1. The site must have quality sand and clay for the manufacture of the brick.
2. The water table of the site must be at least 1m below the level of the kiln floor.
3. The site must have sufficient and suitable clay for the manufacture of the required quantity of the clay.
4. The site must have good access to transportation.

2. Preparation of Brick Earth

The preparation of brick earth involves the following major steps:

1. Unsoiling
2. Digging
3. Cleaning
4. Weathering
5. Grinding
6. Blending
7. Tempering

For a quick view, the preparation of steps is tabulated in the column below.

UNSOILING	DIGGING	CLEANING	WEATHERING	GRINDING	BLENDING	TEMPERING
The top layer of the soil is removed	The clay is dugout from the ground	Cleaning the soil dug. Remove the unwanted debris, stones, and pebbles	The cleaned clay is left in heaps of 60 to 120cm and exposed to the weather.	Crushing rollers are used to grind the clay into a fine powder	The clay is made loose and other required materials are added and blended by harmonious mixing.	In this process, the water is added in right consistency so that a proper blend is obtained
The top layer of soil consists of vegetation and organic matter that is removed in this process	The soil mass is then distributed on a leveled ground ( Below the general ground level)	Excess amount of matter present in the soil will require washing and drying	With atmospheric action, the softening and mellowing of the clay material takes place. Impurities also get decomposed		Blending makes the clay fit for the next stage.	The mix is then kneaded and pressed either by men or cattle to make a stiff and a plastic mix
			Weathering disintegrates big boulders and converts to a uniform mass. Weathering takes from few weeks to full season.			The process is mainly performed in a pug mill. This gives a uniform mix.

Fig.2. Preparing the clay with water for the pugmill

3. Molding of Bricks

The molding of the bricks can be performed either by:

1. Hand Molding
2. Machine Molding

The molds are rectangular boxes, either made of wood or steel.

1. Hand Molding

• In hand molding, the bricks are molded by the hand.
• The hand molding can be either ground molded or table molded
• Ground Molded:  Here, the rectangular mold is placed on a leveled ground and dusted with some sand to avoid sticking of the mold to the ground. The tempered brick mix is dashed into the mold and pressed to fill all the corners of the mold. A metal or wooden strikeis used to cut of excess clay placed in the mold. Once done, the mold is lifted up and the raw brick is left on the ground. The process is repeated.
• Table Mounted: Here the same process is performed over a table. And the bricks are molded over the table.

2. Machine Molding

Machine molding is performed for large scale production and when the clay is very hard to make use of hand molding. The machines used for machine molding are:

1. Plastic Clay Machines
2. Dry Clay Machines

1. Plastic Clay Machines

• Plugged Clay is forced into the rectangular mold
• The molded coming out of the mold is then cut to the required length.
• Cutting is performed by wire
• Hence called a wire cut bricks

2. Dry Clay Bricks

• The dry clay is ground and placed in the mold.
• Water is added to make a stiff paste
• This forms a stiff and hard clay mix.
• This is called as pressed bricks.
• This does not require any further drying process

Both wires cut bricks and pressed bricks to have accurate shape and uniform surface. These are heavy and stronger than hand-molded bricks. Have a distinct frog and exhibits uniform and dense texture.

4. Burning 

The process of burning is performed to completely remove the moisture content present in the brick. This makes the brick, hard and strong hence a dense and durable product is obtained. 

Overburning bricks makes the brick brittle.Underburnt brick are soft. Bricks are burnt either in clamps or kilns which are temporary and permanent burning structures.