The raw material used to make bricks is earth or soil. So let’s start with that.
Soil for Bricks
A good quality soil for the bricks should have the following ingredients.
Let’s have a look at each of the ingredients….
A large quantity of good quality soil is silica. It is 50 to 60 percent. Silica prevents cracks and shrinkage of raw bricks.
A good soil should have 20 to 30 percent alumina. Having alumina ensures the plasticity of soil so that it can mould easily. Presence of excess alumina in soil can shrink and wrap the raw brick during drying and burning.
5 to 6 percent of iron oxide in soil is good for brick. The function of iron oxide is to make bricks reddish. But excess quantity of it can make bricks blue or blackish.
A small quantity of lime is good to have in soil of good quality bricks. Lime prevents the shrinkage of raw bricks. But excess quantity of it can make the bricks to melt and it loses its shape.
About 1 percent of magnesia is good to have in soil of quality bricks. It imparts yellow tint to bricks and reduceshrinkage. But excess quantity of it leads to the decay of bricks.
As we now familiar with good quality soil for the brick. Now it is time for making bricks.
Brick Making Process
Brick making process actually starts from the selection of the site for collecting soil. During site selection a few things should be considered. Such as –
- Selected ground should be plain
- The site is easily accessible for transporting soil
- The site is suitable for workers to work.
After selecting site the brick making process is then done in following 4 steps of operation –
- Clay Preparation
- Drying, and
Clay preparation is done in several steps as given below –
Let’s have a look at each of these steps.
Unsoiling: The top layer of the earth contains impure materials. So we have to dig more to collect clay. Usually a layer about 20 cm of depth is removed from the top surface of earth to collect clay for the bricks. This process is called unsoiling.
Digging: After unsoiling, soil is collected by digging further and spread it on the plain ground.
Cleaning: After collecting clay, impure materials are separatedfrom the clay. If large amount of impure materials are available in clay then it is washed and screened. Then the clay is converted into powder form by roller.
Weathering: in this step of making bricks, the powdered clay is exposed to weather for few weeks.
Blending: If required, ingredients (that we discussed on the Soil for Brick section above) are mixed to clay in this step.
Tempering: In tempering stage, water is added to the clay and mixed. For small scale project mixing is done by castle or by men. But for big scale project it is done by pug mill.
After tempering, the clay becomes plastic and suitable for moulding.
We just have finished the first step of brick making process. Now let’s move to the 2nd step. The 2nd step of brick making process is moulding.
In this step clay is moulded into brick shape (brick shape generally rectangular). Depending on the scale of project it can be done by two ways.
- Hand Moulding (for small scale project)
- Machine moulding ( for large scale project)
Hand Moulding: This process is used for small scale project. For hand moulding, a rectangular wooden or steel mould is used. Hand moulding can be done on ground or on a table.
Whichever you use, ground or table, the process are same and typically involves following procedure –
- Ground is levelled ( for table moulding, table is set up on levelled floor) and sand is sprinkled over it.
- Wetted mould is then placed on ground and filled with tempered clay.
- Extra clay is removed by a wooden or metal strike or with wire.
- After that mould is lifted up and raw brick is left on the ground.
- Same process are followed again for making another raw brick. And the process continues till the required quantities are aquired
Machine moulding: As I told before machine moulding is used in large project where vast quantity of bricks are produced. There are two types of machine are used for this purpose. One is “Plastic clay machine” and another is “Dry clay machine”.
I won’t go in-depth details of how both of the machine are functioned. One thing is to be cleared that both machines are produced raw bricks.
After completing 2nd step of brick making process, we now have the raw brick. The third step is to dry those raw bricks.
The raw bricks, which we found in 2nd step, contains moisture. It should be dried properly. Otherwise while burning, bricks can be distorted and cracked.
Drying can be done artificially or naturally.
In artificial drying, Some kind of dryers are used to dry raw bricks. It usually takes 1 to 3 days.
In natural drying process, raw bricks are stacked in such a way that air can freely circulate among the gaps of raw bricks. In this process 3 to 10 days are required to completely dry the raw bricks depending on the atmosphere.
We have completed the third step of brick making process. The last step of this process is burning.
This is the important step of brick making process. Because brick will gain hardness and strength in this step.
The dried bricks are burned in clamps or kilns. Clamps are usedin the small scale project and kilns are used in large scaleproject.
The dried bricks are burned in 1100 degree celsius. Temperature below 1100 degree celsius and over 1100 degree celsius both can harm the quality of bricks.
If temperature is over 1100 c it can make the bricks brittle. And if the temperature is below 1100 c then bricks will not gain its full strength. That is why burning should be done properly.
By completing burning step, we just have finished the brick making process. Now we have the finished product that is brick which we can use in masonry construction. Now we will see, how we can classified bricks.
Classification of Bricks
If we think in a board sense, we can classified the bricks into two types
- Unburnt bricks
- Burnt bricks
Sometime it is also called sun dried bricks. This type of bricks can only be used in temporary masonry work.
For most of our masonry construction we use the burnt bricks. Burnt bricks can be classified into various types depending on the various criteria.
I’ve written an article about the classification of bricks a few days ago. Read it from below link.
Qualities of Good Bricks
Not all produced bricks are quality bricks. But, how can we select good quality bricks? There are some criteria of it. I have summarised some qualities of good bricks below –
- Bricks should be free from cracks.
- Edges of bricks should be sharp and square.
- Shape of bricks should be uniform and the size of bricks should be standard.
- Brick should give clear ringing sound when struck with metal thing or with each other.
- When scratched with nail finger no impression should be left on brick surface.
- It should be well-burnt and be bright color.
- Brick should have a frog mark.
Those are just common qualities of good bricks. Some days ago I’ve written a details article about this. Read that by clicking on the following link.
How to Justify Qualities of Bricks
Okay. We now know about the qualities of good bricks. But, how can we justify the qualities of bricks?
To know the qualities of bricks several tests can be performed both in laboratory and field. I’ve summarize them below –
- Compressive strength test
- Water Absorption test
- Efflorescence test
- Hardness test
- Size, Shape and Color test
- Soundness test
- Structure test
Read the following post to know more about each of the test.
You already conversant with the types of bricks. I’ll now show you some special types of bricks which we mainly use in some special situation.
Special Types of Bricks
We mainly use this brick types either for some architectural view or for some structural requirements. We generally use the following types of bricks for this purpose –
- Circular Bricks
- Bull Nosed Bricks
- Squint Bricks
- Perforated Bricks
- Hollow Bricks
- Coping Bricks
- Paving Bricks
- Cornice Bricks
Circular Bricks: Internal and external faces of this type of bricks are circular. These bricks are used in circular shaped structure. Such as well.
Bull Nosed Bricks: Forming rounded quoins this type of bricks are used.
Squint Bricks: This type of bricks are cut to an oblique angle for various construction purpose.
Perforated Bricks: In this type of bricks some perforations run through their thickness. These bricks are used for load bearing walls of low height building and for panel walls of multistoriedbuildings.
Hollow Bricks: One or more cavities are formed in this type of bricks. These are used for load bearing walls, partition walls and panel walls.
Coping Bricks: These bricks are mainly used on top of boundary wall.
Paving bricks: This type of bricks are specially made for roads and highway.
Cornice bricks: This type of bricks are used to increase the architectural beauty of the structure.
When bricks unloaded on my project I always check their quality by viewing their color, uniformity, shape and hardness by nailing if they are suitable for my construction or not.
In this post I shared everything you should know about the bricks as a construction professional. If you like this post please share with your friends.