Mastercivilengineer

Introduction

Brick is a building material made of hard inorganic clay of a size that can be conveniently handled. Bricks can be easily arranged into various shapes for most of the structures. The strength of brick masonry works depends upon the quality of bricks, type of bond, proportion, and quality of materials used in the mortar.

Bricks are either made by hand or machine moulded from suitable clay and properly burnt in kilns. Bricks should be sound, hard, homogenous in texture and free from cracks, flaws, and modules of free lime. Bricks are either of deep red, cherry, or coffee color. They must have regular shape and size and should have sharp, square edges and parallel faces. Bricks should be free from pores, chips, flaws, or lumps of any kind. When sounded they should give clear metal ringing sound.

Bricks should be provided with frogs. Only full-size bricks should be used for masonry work. Bricks bats should be used only with the permission of the engineers to make up required wall length or for bonding.

Requirement of Bricks

Common building bricks must have a minimum compressive strength of 50 kg/sq.cm, when tested as per, IS 3495.

However, the compressive strength of common burnt clay bricks generally varies from 25 kg/sq.cm to 50 kg/sq.cm depending upon the technique used to manufacture and the place where it is made. The quality of bricks is generally found to be deteriorating and hence it is rapidly being substituted by concrete blocks and other materials.

Dimensions

The standard size of common building bricks should be as follows:

Length in centimeter (cm)	Width in centimeter (cm)	Height in centimeter (cm)
19	9	9
19	9	4

Measurement of Tolerances of Burnt Clay Building Bricks

The dimensions of bricks when tested shall be within the following limits per 20 bricks as given below:

Subclass A

• Length 368 to 392 cm (380 ± 12 cm)
• Width 174 to 186 cm (180 ± 6 cm)
• Height 174 to 186 cm (180 ± 6 cm) in case of 9 cm high bricks
• Height 77 to 83 cm (80 ± 3 cm ) in case of 4 cm high bricks.

Subclass B

• Length 368 cm to 392 cm (380 ± 12 cm)
• Width 174 to 186 cm (180 ± 6 cm)
• Height 174 to 186 cm (180 ± 6 cm) in case of 9 cm high bricks
• Height 74 to 86 cm (80 ± 6 cm) in case of 4 cm high bricks.

Quality of Bricks

Method of Measuring Dimensions

According to the size of the stack, twenty whole bricks should be selected at random for the sample. All blisters, loose particles of clay, and small projections should be removed. The bricks should be arranged on a level surface successively in such a way that the sides of the bricks should be in contact with each other and in a straight line. The overall length of the assembled bricks should be measured with a steel tape to measure the whole row at one stretch. All the dimensions should be added together.

Compressive Strength

The unevenness in the bad faces of bricks must be examined and should be removed by grinding. The bricks are required to be immersed in water for 24 hours. The specimen should be removed and the surplus water should be drained out at room temperature after this, the frog in the brick should be filled with cement mortar and brick stored in damp jute for 24 hours followed by immersion in water for 3 days. Thereafter, the specimen brick should be wiped and subjected to a compressive test in flat position at a uniform rate of 140 kg/sq.cm/minute till failure occurs.

Water Absorption   

After drying a specimen brick in a well-ventilated oven at 105^oC to 115^oC the brick should be cooled to room temperature and then immersed in clean water for 24 hours. Average water absorption should not be more than 20% by weight for bricks of class 35 kg/sq.cm to 125 kg/sq.cm compressive strength.

Efflorescence

A shallow flat bottom dish over 150 mm in diameter and 30 m in depth containing sufficient distilled water capable enough to completely saturate the specimen is used. The dish can be made of glass, porcelain, or glazed stonework.

The end of the bricks is placed in the dish, such that the depth of immersion in water is 25 mm. the entire arrangement is placed in a warm well-ventilated room until all the water in the dish is absorbed by the specimens and the surplus water evaporates. After the water has been absorbed and bricks appear to be dry, a similar quantity of water in the dish is now added and allowed to evaporate as before. The bricks are examined for efflorescence after the second evaporation and observations are noted as per guidelines given below:

Bulk Density

The bulk density of heavy duty bricks should not b less than 2.5 gm/Cum.

Mortar

Mortar is a bonding material formed by the addition of water to a mixture of sand and cement which is manually or machine mixed and applied with a trowel. The mortar bonds the individual bricks together.

Generally, cement, sand, mortar is used in construction work both of temporary or permanent nature. However, in rural areas mud mortar or lime mortar is also used.

In mud mortar, the soil with a clay content of 10 to 20% is ideal for making mud mortar. Moisture reduces the compressive strength of masonry drastically. Basic stresses for masonry in mud mortar, both in dry & moist conditions, have been arrived at known strength of bricks. It varies from 1.5 N/mm2 to 4.0 N/mm2 in dry condition and from 1.3 N/mm2 to 3.3 N/mm2 in a moist condition.

The sand used in mortar shall be free from clay, alkali, and organic matter and shall be sound, hard, clean, and having durable particles.

Preparation of Mortar

The ingredients of cement mortar shall first be mixed thoroughly in dry conditions. Water shall then be spread uniformly and mixed continuously to give a uniform mix of the required consistency. Cement sand mortar shall preferably be machine mixed trough hand mixing in a through the manner that may be allowed. The mortar mixed so mixedly shall be used within 25 to 30 minutes of its preparation especially during high ambient temperatures. Mortar left unused if stiff and unworkable should be rejected. Estimated quantities of cement, sand, and bricks required per CuM of brickwork are given in the below table.  

Estimated quantities of material required per cubic meter of brick masonry.

Guidelines for Construction of Brick Masonry

• In the brickwork, the bricks should be laid with an adequate gap between them on their bed with the frogs pointing upwards so that mortar gets a mechanical bond/key between the two layers of bricks.

• The brick courses should be laid truly horizontal & should have truly vertical joints.

• Unless unavoidable the use of brick bats should be discouraged.

• As far as possible the brick walls should be raised uniformly with a proper bend. Generally, the height of brick masonry construction should be less than 1.5 m in a day. the maximum difference in height of the wall between the different portions should not be more than one meter.

• When the mortar is green, the facet joints should be raked to a depth of 12 to 19 mm in order to have a proper key or plastering or pointing. In brick masonry, the mortar joints should be stuck flush and finished if no plastering or pointing is to be done.

• Finished brickwork in cement mortar should be cured for a period of one week at least before plastering it.

• In order to carry out the brickwork at a higher level, double scaffolding should be used. Single scaffolding results in holes being left masonry which is not recommended as it can cause subsequent leakages.

Tools for Brick Laying

Trowel

A trowel is used for lifting and spreading mortar for forming joints and also for cutting bricks.

Plumb bob and Float

Plumb bob is used for checking the verticality of the surface of masonry.

Straight edge is smooth and straight wooden, aluminum or steel piece 2 m long and about 10 cm wide and having a suitable thickness. This is used to check the horizontality of masonry in tandem with a water tube on the spirit level.

Spirit Level

This is simple device to check the horizontality of the masonry.

Set Square

This is a right angle steel section for checking perpendicularity of the masonry surfaces at the opening and also for checking right angles at the corners.

String

In order to maintain the correct alignment of the courses about 10 m. a long cord is stretched between two quoins of the wall.

Boaster

In order to cut the brick accurately a steel chisel with a very wide blade is employed.

Brick Hammers

These are of two types scabbling hammer and waller’s hammer. These hammers are used for cutting bricks to different shapes and sizes. One end of these hammers is square and the other end has a sharp edge.

Raking Tool

This tool has a sharp edge and is used to rake the mortar joints in brick masonry.