Village Level Brickmaking (GTZ, 1989, 124 p.) Standardization Introduction Form Size Quality Strength Using Bricks In Construction Moulds

Village Level Brickmaking (GTZ, 1989, 124 p.)

Standardization

Introduction

Standardization is an agreement between a group of producers or manufacturers stating that the product which each one produces will have the same characteristics.

For example, a person who owns a small portable radio can purchase batteries for it made in Europe, Africa or Asia and know that the batteries will fit in the radio. This is because the size, shape and power of the batteries have been standardized.

Figure

It is also important to standardize the characteristics of bricks made in an area. These characteristics are:

1. Form
2. Size
3. Quality
4. Strength

The Benefits of Standardization

Many builders and contractors do not like to use bricks made by small independent producers because the bricks can vary a great deal in form, size and quality. For example, one producer may make a brick 240 mm × 115 mm × 77 mm and another in the same area may make a brick 220 mm × 100 mm × 65 mm. Because the sizes differ, it is difficult for a builder to mix these bricks when building a wall. A large contractor may need 500,000 bricks annually, yet many small producers will only have 100,000 bricks available to sell each year. If the contractor bought 100,000 bricks from 5 different producers who each produced a different brick, it would cause many problems for the builders.

Another advantage of standardizing the bricks is being able to accurately calculate the number of bricks needed to construct a building. It also means that the size of the openings (e.g. doors and windows) can be calculated and can be made before the building is built.

Before starting to make bricks, contact all the other producers near you as well as contractors, builders and the local public works department and together agree on the form, size, quality and strength of the bricks that will be produced.

If there are no existing standards in your area, the following pages will help you to establish your own local standards.

Form

There are two general types of back forms:

1. Hollow Clay blocks
2. Solid Clay bricks

Figure

Hollow Clay Blocks

Normally these types of blocks are made in a back factory with special machines and equipment. In rural areas, it is also possible to make hollow blocks with wooden moulds but the results are often unsatisfactory.

Builders often like using hollow blocks because the larger size allows them to build a house in less time than with smaller solid backs. However, hollow clay blocks also have the following disadvantages:

- a special permanent kiln is necessary to fire them correctly,
- the blocks can not be used to build arches, and
- more cement and steel is usually required for reinforcement end plastering

Figure

Solid Clay Bricks

Solid clay bricks are better for a small rural producer to make because:

The form is simple. It is much easier to make the mould and easier to mould the brick so there is less chance of a poorly formed brick.

You do not need a permanent kiln. It is possible to build and fire a simple clamp or field kiln.

The bricks have good strength and can carry the weight of a heavy roof without steel and concrete reinforcement.

They can be used to build arches.

If the bricks are made and fired well, it is not necessary to render or plaster the wall, and therefore building materials are saved.

The bricks can be used to pave a floor.

Figure

Size

A brick has a length, width and height. The size or dimensions of a brick are determined by how it is used in construction.

Figure

Width

The width of a brick should be small enough to allow a bricklayer to lift the brick with one hand and place it on a bed of mortar. For the average person, the width should not be more than 115 mm. If the brick was wider, the bricklayer would have to put down the trowel while building the wall to pick up the brick with two hands and as a result, time would be wasted. In addition, a wider brick would weigh more and therefore tire the mason more quickly. In terms of brickmaking, a larger brick is also more difficult to fire in a kiln.

Figure

Length

There is a very important relationship between the length of a brick and its width because of how we use bricks to build a wall.

Figure

The length of a brick should be equal to twice its width plus 10 mm (for the mortar joint). A brick with this length will be easier to build with because it will provide and even surface on both sides of the wall.

For example, if you follow the rule of the length being twice the width plus 10 mm, if you would like to have a brick 115 mm wide, then the ideal length would be 240 mm.

115 mm (width of brick)
115 mm (width of back)
+10 mm (thickness of mortar joint)
———
240 mm (length of brick)

Height

The height of a brick, though of less importance, also has a relationship with the length of the brick. The height of three bricks plus two 10 mm joints should be equal to the length of a brick. This allows a bricklayer to lay bricks on end (called a soldier course) and join them into the wall without having to cut the bricks.

Figure

To determine the height of a brick, subtract 20 mm (the thickness of the two 10 mm mortar joints) from the length and divide the result by three (this represents the three bricks).

Possible Brick Sizes

Therefore, using these rules, the largest size brick that would still permit a bricklayer to comfortably pick it up with one hand, would be 240 ram in length, 115 mm in width and 73 mm in height. A brick of this size would weigh about 3.5 kg.

Figure

Every country in the world seems to have a different size of brick. The sizes are a result of centuries of tradition or custom but almost all use the same rules and lie within the limits mentioned. No one size is better than the other. In India the standard brick size is 190 mm × 90 mm × 40 mm while the British standard is 215 mm × 102.5 mm × 65 mm.

To choose your brick size, first contact the local public works department to see if your country has a standard size. If not, you will have to choose your own size based on the rules listed in this chapter. Possible brick sizes that you could choose from are shown in the chart.

Possible Brick Sizes
Length	Width	Height
240 mm	115 mm	73 mm
230 mm	110 mm	70 mm
220 mm	105 mm	67 mm
215 mm	102 mm	65 mm
210 mm	100 mm	63 mm

Minimum and Maximum Dimensions

Each fired brick will not be exactly the same size; they will vary a little for many reasons. Ideally, these variations in dimensions should be limited because many contractors prefer to have a guarantee that the bricks they buy will be between certain predetermined limits.

The bricks manufactured in rural areas should have a tolerance of approximately 5%. This means that if the brick size is 240 mm × 115 mm × 73 mm, the length of the brick should fall between 235 mm and 245 mm. The width should be between 112 mm and 118 mm and the height between 71 mm and 75 mm. Bricks with dimensions outside of this 5% limit should be set aside and not sold.

Figure

Quality

A good quality brick should be regular in shape and size, with smooth even sides and no cracks or defects.

Normally poor quality bricks are a result of using poor techniques when making the bricks but these errors can often be easily corrected. You will find a list of solutions to various problems on pages 48 to 49. If you do have very poor quality bricks, do not sell them or build with them

Figure

Strength

Bricks must have enough strength to carry the weight of the roof. If bricks have been well- made and well-fired, you will hear a metallic sound or ring when they are knocked together. If they make a dull sound, it could mean that they are either cracked or underfired.

Figure

A simple test for strength is to drop a brick from a height of 1.2 metres (shoulder height). A good brick will not break. This test should be repeated with a wet brick (a brick soaked in water for one week). If the soaked brick does not break when dropped, the quality is good enough to build single storey structures. Note: should the bricks dissolve or fall apart underwater, the bricks were probably underfired.

Figure

Using Bricks In Construction

If you are going to produce bricks, it is important to know some very basic facts about how bricks are used in construction and how to calculate the number of bricks which will be needed to build a building.

Wall Thickness

Internal Walls: The walls inside a building which do not carry the weight of the roof usually have a thickness of half a brick. The term half brick refers to half the length of the brick which is equal to the width. These internal walls should not be subject to shocks, vibrations, etc..

Internal Walls

The drawing shows an internal wall being constructed. If the brick used is 240 mm long by 115 mm wide by 73 mm high, the thickness of the wall is half a brick or 115 mm.

Internal Wall (1/2 brick wide)

External Walls: The walls on the outside of a building which carry the weight of the roof usually have a thickness of one brick. The term one brick thick refers to the full length of a brick.

External Wall

The drawing shows an outer wall being constructed. If the brick used is 240 mm long by 115 mm in wide by 73 mm in high, the thickness of the wall which is a full brick wide is 240 mm

External Wall (full-brick width)

Quantity

It is possible to calculate the number of bricks that will be necessary to build each square metre of wall. This will help the builder or contractor to calculate the number of bricks which must be bought to build a building.

Figure

For example, if you have bricks 240 mm × 115 mm × 73 mm, the builder should buy SO bricks for each square metre of interior wall with a thickness of half a brick or 115 mm. If an interior wall is 2.5 metres tall by 3 metres long, you would need 375 bricks (2.5 m × 3 m × 50 bricks/m²= 375 bricks).

For an external wall one brick thick or in this case 240 mm, a builder should buy 100 bricks per square metre of external wall. If for example, an external wall is 6 metres long by 2.5 metres high, you would need to buy 1,500 bricks to build that one wall (6 m × 5.5 m × 100 bricks/m²= 1,500 bricks).

Figure

Mortar Joint

Brick mortar can be made from lime, cement or mud. The purpose of the mortar is to join the bricks together in a certain fixed position and to smooth out the irregularities in the shape and size of the bricks. This is necessary in order to transmit the load or weight correctly and evenly throughout every part of the wall.

Figure

The strength of the mortar should be less than that of the brick. This will prevent the bricks from cracking when a wall or a foundation settles. If movement does occur, it is better to have the mortar crack instead of the brick because it is easier to repair or replace mortar than a brick.

The strength of a wall is also affected by the thickness of the mortar joints. A mortar joint, especially if made with lime, of 20 to 30 mm is much weaker than a joint of 10 mm. For a strong wall, all mortar joints should be 10 mm thick.

Moulds

Because all clay shrinks when dried and fired, brick moulds must be larger than the final size of the bricks. Good brickmaking clays shrink between 5% and 11% and therefore the moulds should be 5% to 11% larger than the final size of the fired brick.

Figure

The following table gives the interior dimensions of a mould for various clay shrinkage rates which will produce a 240 mm × 115 mm × 73 mm fired brick. Information on how to make the mould and tables for other bricks with different dimensions can be found in Appendix 2.

Note: It is essential to accurately calculate the shrinkage of the clay. Contact your local public works department for assistance.

Shrinkage Rates And Mould Sizes
Fired BrickSize: 240 mm × 115 mm × 73 mm .

Shrinkage	Interior Mould Size
Rate	Length	Width	Height
5%	253 mm	121 mm	77 mm
6%	256 mm	122 mm	78 mm
7%	258 mm	123 mm	79 mm
8%	261 mm	125 mm	80 mm
9%	264 mm	126 mm	81 mm
10%	267 mm	128 mm	81 mm
11%	270 mm	129 mm	82 mm
12%	273 mm	131 mm	83 mm

Stages Of Brickmaking

There are two main stages in the production of bricks. They are:

A. Forming the brick, and
B. Firing the brick.

Within each of these, there are several important steps:

A. Forming the brick:

- extraction of the clay
- clay preparation
- moulding or shaping
- drying

B. Firing the brick:

- building the field kiln
- firing the field kiln

Each of these steps will be dealt with in detail in the following chapters.