Bricks & Blocks

Our 1st development on 11/2/2012 

This is how to make a home-made brick ^^

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INTRODUCTION

Masonry means any structure built by stacking or bonding together discrete pieces of rock, fired clay, concrete, etc

The great majority of masonry work is produced from preformed units, bonded by mortar. The preformed units are usually of;

·         Bricks, and

·         Blocks

Each of these forms has advantages;

-          the smaller size of bricks produces attractive appearances, especially in facing clay bricks, and makes handling easier.

-          the larger blocks permit rapid and economical construction, give better strength, finishes, densities and thermal properties.

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BRICKS

General

Bricks should meet the following requirements;

-          Be of sufficient strength, at least to be able to take the self-imposed load,

-          Be durable- being able to withstand weathering and exposure to the elements,

-          Aesthetic appeal - should be of good appearance if used in facing brickwork, and

-          Of regular shape and size to facilitate bonding. In its most common form, a brick can be held in one hand, and its length equal to 2 widths and 3 heights. The usual dimensions are 215x100x65mm.

Some bricks have a frog; depression on one or both bed faces.

What is the use of a frog?

Bricks are made in four materials:

-          Burnt or fired clay

-          Calcium silicate

-          Dense concrete

-          Lightweight concrete

However, there are bricks made of certain materials and fired to certain temperatures to meet special requirements in use, such as in fire bricks, chemical resistant bricks, engineering bricks, etc.

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5 Simple Step to Produce Brick

Step 1: Begin by collecting the perfect dirt for brick-making. You will need to dig down atleast one foot, collecting deeper, lighter colored dirt and not the top soil. Sift the rocks and twigs from the dirt and place it in a wheelbarrow. You can use a household strainer to sift the dirt, if desired.

Step 2 : Add grass or straw to the dirt. As a general rule you should add one part grass or straw to six parts dirt. The grass or straw should be cut short, no longer than 3 inches in length.


Step 3 : Stir in water slowly, mixing well. Add only enough water so that the dirt is thick, not runny, about the consistency of biscuit dough. It is important to mix thoroughly, preventing the dirt from clumping up and forming brittle, dry patches in your finished brick.

Step 4 : Shovel the mud into your chosen mold. Molds can be made from many things such as old milk cartons, ice cream containers, pie pans or you can make your own mold from scraps of wood.


Step 5 : Place the molds, full of mud, in the sun to dry. When partially dry you can add decorative touches, such as hand or foot prints, glass beads or shards or anything you can imagine. Once the bricks are dry enough, remove them gently from the mold and place them in a dry, shaded area to complete drying. Placing them in the shade for the final drying will help prevent cracking.


Tips & Warnings when making brick
Strengthen your bricks by adding one part gypsum, lime, cheese whey or manure.

From
http://www.ehow.com/how_2121365_make-bricks.html

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Clay Bricks

Properties of clay bricks that are important in use;

1. Crushing strength
2. Porosity/water absorption
3. Durability
4. Moisture movement
5. Appearance
6. Fire resistance
7. Sound insulation
8. Efflorescene
9. Thermal insulation
10. Flexibility in applications

Crushing strength

Clay bricks have high compressive strength. Bricks made by modern de-aerated extruder and fired to sufficiently high temperature can withstand compressive strength exceeding 28 N/mm². For this reason they are suitable for load-bearing structures.

However, it should be noted that there can be wide differences in strength in individual bricks, especially those made with poor quality control.

Porosity/water absorption

In contrast to bricks made from other materials, the porosity of clay bricks is attributed to its fine capillaries. The fine capillaries enable brickwalls to ‘breathe’, i.e., moisture is released during day-time and re-absorbed during night-time. The ability of clay bricks to release and re-absorb moisture by capillary effect helps to regulate the temperature and humidity of atmosphere in a building. This distinctive property makes clay bricks a particularly suitable building material for houses in the tropics.

On the other hand, all porous materials are susceptible to chemical attack and are liable to contamination from weathering agents such as rain and polluted air.  To mitigate the adverse effect and at the same time retain the advantages associated with porosity, the rate of water absorption of clay bricks for masonry work should preferably be kept to around 10%.

Another important property of clay brick related to porosity is its initial rate of absorption (IRA). The IRA affects the strength of the bond between bricks and mortar during bricklaying. High IRA removes too much water from the mortar rapidly and thus prevents proper hydration of cement, resulting in low strength of the bond between bricks and mortar.

Generally bricks with IRA exceeding 2kg/m²/min will gives rise to difficulties in laying using common cement mortars.

Durability

Durability of bricks depends on;

- the amount of soluble salts, especially sulphates, present in the brick

- the firing temperature

Generally well-burnt clay bricks are extremely durable.

Moisture movement

What is moisture movement?

Moisture movement can be termed reversible or irreversible.

Reversible moisture movement  clay bricks is less than that of calcium silicate bricks and concrete bricks. This is usually negligible and is of no practical significance.

However, irreversible moisture movement (expansion) of clay bricks (due to absorption of moisture from the atmosphere) is high which may amount to between 0.1 to 0.2 per cent. Because about half of this movement takes place in the first 7 days after firing, it is recommended that at least a week should pass before the bricks are used, particularly if they are to be laid in a strong mortar.

Appearance

Appearance in common clay bricks is not important, where masonry works constructed from them are plastered. However, good appearance is an important property in facing bricks. Appearance can be in the form of  colours or textures.

Colour of bricks is either integral or superficial. Integral colours are the natural colours that come from firing of the various clays from which the bricks are made. These colours include red, white, yellow, brown and blue. Superficial colours (used in many facing bricks) are achieved by the addition of inert mineral oxides to the faces of bricks before firing.

Texture of bricks are achieved by;

- method of forming

- mechanical treatment

- blasting of sand or particles onto surface of bricks when green.

Fire resistance

Fire resistance is an inherent property in bricks.

Why is this so?

A 100mm thick clay brickwork with 12.5mm thick plastering can provide a fire-resistance of 2 hours and a 200mm thick similar wall non-plastered can give a maximum fire-rating of 6 hours.

Sound insulation

Well constructed clay brickwork provides good insulation against air-borne sound in proportionate ratio to its density and thickness. However, bad brick-laying leaves small gaps for sound to pass through a wall.

The sound insulation of well-constructed brickwork is generally 45 decibels and 50 decibels for 4½” (112.5mm) thick and 9” (225mm) thick brickwalls.

Efflorescene

All clay bricks contain some soluble salts. Soluble salts come from the original clay or from its reaction with sulphur compounds from the fuel used for firing bricks.

Soluble salts in bricks together with lime compounds in the cement-lime mortar, may be carried to the surface and crystallize as a white deposit (called efflorescence). The extent to which efflorescence appears depends on;

-  the amount and solubility of salts present in the bricks, and

-  wetting and drying conditions.

Efflorescence is harmful to the brickwork as it;

-  mars the appearance of the brickwork, and

-  lessen its durability.

Thermal insulation/conductivity

Clay bricks generally exhibits better thermal insulation property compared to many other building materials such as concrete, timber or concrete blocks. Perforations can improve the thermal insulation of bricks.

Thermal insulation/conductivity of bricks varies proportionately with;

- density

- moisture content

Flexibility in applications

Clay bricks are used for a wide range of applications in buildings and engineering structures. They can be used in following structures;

- loadbearing walls

- non-loadbearing partition walls and decorative walls

- earth retaining walls

- manholes and drain sumps

- furnaces, kilns and flues

- fencings

Bricks can be made into convenient shapes and sizes to make them handy and flexible in application.

Types of clay bricks

The most common types of bricks in use are:

1. Common brick

2. Facing bricks

Common clay bricks are those used for general purposes, where appearance is not important. Usually they are used in walls where the surfaces are plastered.

Facing bricks are bricks required to have good appearance and they are specially made with good quality control. In Malaysia there are a number of factories making these bricks of high quality. Facing bricks are classified according to the texture of their surfaces, with names like;

- smooth face

- rock face

- sandblast

- cobble

- ledge brick

- castle brick

Brick veneers or veneer tiles are used purely for decorative purposes whereby they are bonded onto walls/panels to give the effect of facing bricks.

Brick Accessories and Specials

Bricks accessories and bricks of special shapes are made to cater to specific needs. These can be:

- single bullnose

- double bullnose

- window sill

- copping

- copping corner

- ventilation brick/block

- dogleg

Perforations, keys, frogs and cellular voids are common features in clay bricks. They are made to meet certain requirements.

Manufacture of Clay Bricks

Bricks are made from clays which composed of silica and alumina and various impurities including iron compounds, magnesia, potash, etc.

The main processes in the manufacture of clay bricks involve:

- preparation

- forming

- drying and firing

Preparation

This involves the removal of stones and other undesirable particles, and in some cases the addition of fuel or other organic compounds. The burning of the organic material during  firing contributes to the heat and thus save fuel. Also the burning out of these materials leave a more open, lower density structure in the bricks.

Forming

The wet clay must be formed to dimensions which allow for shrinkage in firing later. Forming can be done in 4 ways;

Soft mud process

The clay is blended with 25-30% water using mixers. The mud is formed into lumps of the size of one brick and the lumps dipped in sand to reduce the stickiness of the surface. The lumps are then manually or mechanically placed and formed in moulds, with excess mud cut off with a wire. Because of the high drying shrinkage of such wet mixes and the plasticity of the the green brick, the shape and size of such units are fairly variable. However the finished brick is fairly porous which improves its insulation properties and its effectiveness as a rain screen, but limits the strength.

Stiff plastic process

The clay is blended with 10-15% water to make a very stiff but plastic compound. This is then extruded from the mixer and cut into brick-shaped pieces and allowed to dry for a short period before being press in a mould. The clay, being very stiff, when ejected from the mould retains exactly the shape of the mould. The low moisture content in this process leads to the following advantages;

- shrinkage of brick after firing is low

- size of the brick is easier to control

- the drying time is relatively short.

The process is used to produce engineering bricks, facing bricks and bricks where very accurate dimensions are required.

Wire cut process

In this process, clay of a softer consistency (with moisture content of 20-25%) is extruded from a rectangular die. The ‘column’ of clay is then cut into bricks by wires. The process is fully continuous.

Perforations are usually made along the length of the ‘column’ to produce perforated bricks. Perforations in bricks give the following advantages;

1. Reduction in the quantity of clay required per unit of brick, thus reducing costs of production and in transportation.

2. A reduction in environmental impact by reducing the rate of use of clay deposites.

3. Opening up of more surface area in the unit of brick, thus speeding up drying and firing.

4. Thermal insulation is improved with the existence of air voids in the brickwork.

5. The lighter units of bricks are less tiring to lay.

Pressing

In this process, stiff clay, without addition of water is formed into bricks by mechanical pressure (pressing). This obviates the need for drying the green bricks in a separate drier.

Drying and firing

‘Green’ bricks must be dried before they are fired. Drying is usually done in separate drier or in the drying zone of a continuously fired kiln.

Process of bricks building

The great majority of bricks are fired in continuous kilns. A very efficient way of mass-producing bricks is to use tunnel kilns, in which the bricks, usually pre-dried, are moved through a stationary fire.

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Calcium Silicate Bricks

Manufacture of calcium silicate bricks

Controlled proportions of sand and flint are mixed with hydrated lime, and these are pressed under high pressure. Pigments may be added for colours.

After pressing, the bricks are steamed at pressure up to 1.7 N/mm²  for about 8 hours in an autoclave. During the steaming process, the lime reacts with the surfaces of the silica particles forming hydrated calcium silicate.

When exposed to the atmosphere, the calcium silicate gradually reacts with carbon dioxide and form calcium carbonate, thus giving the bricks the strength and hardness.

Properties of calcium silicate bricks

Strength

Strength of calcium silicate bricks is comparable to clay bricks. However, they cannot achieve the extremely high strength of engineering clay bricks (of around 50N/mm²).

Unlike clay brick, strength of calcium silica brick are more uniform.

Moisture movement

The extent of moisture movement (reversible) in calcium silica bricks is greater than clay bricks but lower than concrete bricks. Wet silica bricks built into large panel wall can cause the wall to crack when dry, especially if a strong mortar is used. To prevent cracks, the following actions need to be taken;

1. If available, use bricks with a reversible moisture movement (drying shrinkage) of lower than 0.04%.

2. Keep the bricks as dry as possible before and during construction.

3. Use a mortar which contain no more cement than is required. This will give a weaker mortar to accommodate the moisture movement.

Durability

Calcium silica bricks have satisfactory durability. However, they should not be used in the following circumstances:

1. Where they would come into contact with sewage.

2. Where they will be exposed to strong acids.

3. In areas of high concentration of magnesium or ammonium sulphates, e.g in industrial wastes.

4. Where they will be repeatedly wetted by sea water or solutions of  sodium chloride or calcium chloride.

Appearance

Calcium silicate bricks, being formed by pressing followed by steaming, have sharp arrises and high uniformity in size, shape, colour and texture.

Colour – in our country the natural colours are white or off-white depending on the aggregates used. Other colours can be obtained by adding pigments to the mix before pressing.

Texture – are usually smooth and fine-textured.

Fire resistance

Fire resistance is good but calcium silicate brickwork need to be thicker to achieve 3 and 4 hours fire resistance.

Absorption

The water absorption of calcium silicate bricks is generally higher than clay bricks.

Sound and thermal insulation

Calcium silica bricks have sound and thermal insulation equivalent to clay bricks of same density.

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Concrete Bricks

Concrete bricks are harder, more difficult to cut and less pleasant to handle than clay or calcium silica bricks.

Drying shrinkage (reversible moisture movement) varies considerably and is greater than both the other types of bricks. As with calcium silica bricks, special care need to be taken in selection, design and in construction to avoid cracking of brickwork after laying.

In Malaysia, quality control of concrete bricks is poor and varies considerably from manufacturer to manufacturer.

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Bricks Quality
There are three basic types of bricks

• First Class Bricks                                         
• Second Class Bricks
• Third Class Bricks

Specification of First Class Bricks

• Made of good earth which is free from saline deposits and are sand molded.
• Burnt thoroughly without being vitrified and have deep red, cherry and copper color. 
• Regular and uniform in shape and size with sharp and square edges and parallel faces. 
• Must be homogeneous in texture and emit a clear ringing sound on being struck together.

Specification of Second Class Bricks

• They shall be well burnt or slightly over burnt.
• They must give clear ringing sound when struck.
• The may have slight irregularities in size, shape and color.
• They may have slight chips, flaws or surface crack but must be free from lime or kankar.
• The minimum crushing strength of second class brick should be 70 kg per sq cm. 

Specification of Third Class Bricks

• These bricks are slightly under burnt or over burnt.
• They are not uniform in shape, size and edges.
• They shall not observe water more than 25% of their own dry weight after 24 hours, immersion in cold water.
• They have some signs of  efflorescence.

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Terms and Various Basic Positions and pattern

Bull Header : A rowlock brick laid with its longest dimensions perpendicular to the face of the wall. 

Bull Stretcher : A rowlock brick laid with its longest dimension parallel to the face of the wall. 

Course : One of the continuous horizontal rows of masonry that,bonded together, forms the masonry structure. 

Header : A masonry unit laid flat with its longest dimension perpendicular to the face of the wall. It is generally used to tie two wythes of masonry together. 

Rowlock : A brick laid on its face, or edge. 

Soldier :  A brick laid on its end so that its longest dimension is parallel to the vertical axis of the face of the wall

Stretcher : A masonry unit laid flat with its longest dimension parallel to the face of the wall. 

Wythe : A continuous vertical section or thickness of masonry 4" or greater.

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BLOCKS

Blocks are larger than bricks. For this reason a block usually requires both hands to lift it for laying. However, because they are larger, they can be laid more quickly than bricks, but the bigger size also means less versatility in laying especially when building up ends or corners and also laying to curves.

Generally blocks are intended to be plastered.

Types of blocks:

1. Clay blocks

2. Concrete blocks

Between the two, concrete blocks are more widely used.

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Clay Blocks

Clay blocks are generally extruded hollow units (see Fig 6.6). The material used in their manufacture is the same as clay bricks. After firing, clay blocks are dense, hard and brittle which make them difficult to cut and fix.

Sizes

The standard formats (sizes) for wall blocks are as shown in Fig 6.6.

Strength

The minimum average compressive strengths for clay blocks are;

Non-loadbearing walls/partitions              1.4 N/mm²

Facing and common blocks                       2.8 N/mm²

Blocks for loadbearing internal walls        2.8 N/mm²

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Concrete Blocks

Concrete blocks are termed either dense or lightweight. Lightweight concrete blocks can be one-third the weight of dense blocks. Lightweight blocks have the following advantages;

 - easier to handle and quicker to lay,

 - the air in lightweight block provide better sound and thermal insulation,

 - the lighter weight results in lighter foundations and structural members, and

 - they can be cut and chased with hand tools and hold nails and screws without plugs.

Lightweight concrete blocks are used mostly in internal wall partitions.

Types of  concrete blocks

Solid blocks – no formed holes or  slots.

Cellular blocks – with cavities (holes) which do not pass through.

Hollow blocks – with cavities which pass through.

Sizes

Table 6.9 gives the typical work sizes.

Strength

The minimum crushing strength of concrete blocks are given below:

	Concrete density1 kg/mm3	Strength N/mm2
Dense aggregate	1500-2000	2.8-3.5
Lightweight aggregate	700-1500	2.8-10.5
Autoclaved aerated	400-900	2.8-7.0

¹ Weight of block divided by overall volume.

Drying shrinkage

Shrinkage cracks can be avoided by the use of blocks with low drying (reversible) shrinkage, and by taking the necessary precautions described for calcium silicate brickwork.

Thermal and sound insulation

Thermal conductivity of blocks varies with density. Lightweight concrete blocks have better thermal insulation compared to denser blocks.

Fire resistance

Fire resistance of concrete blocks is good.

Durability

Durability of facory-made blocks is generally good. Blocks made with dense aggregate and having a compressive strength of at least 7 N/mm²  can be used for external walls and below ground level as damp-proof courses.

Appearance

The appearance of concrete blockwork depends on the quality of blocks and mortar used. For good appearance the bonding pattern and quality of workmanship is also important.