Tag: Bricks

Efflorescence in Brick Work

Efflorescence in Brick Work

When soluble salts are present in huge quantities in the bricks or in the mortar, they absorb moisture from air or during construction progress and are brought to the surface in solution and deposited in concentrated patches either in the form of white powder, stains or as translucent crystals, as the moisture eventually dries out.  The appearance of these crystals either flakes off or it is reduced to powdery form that can be easily brushed off.  Attempting to seal off efflorescence in brick work is not advisable and it is not recommended to do white wash or rendering the walls before it gets dried off.

The soluble salts can be removed by frequent repeated washings with clean water and brushing the face of the masonry.

The salts from brickwork can also be removed with a solution of zinc sulphate and water. For this application, the surface that has to be treated should be brushed off thoroughly and allowed to dry. A solution containing 1 part of hydrochloric acid or sulphuric acid with 5 parts of water is applied vigorously with scrubbing brushes and water is being constantly sprayed on the work with a hose to prevent the penetration of acid. By doing so, this helps in removing white or yellow blotches from floors or walls due to efflorescence.

Effloroscence in Brick Work

Cleaning of external brick walls after completion of the building can be done with a 5 percent solution of muriatic acid. The walls must be thoroughly washed with copious flow of clean water both before and water the application of the solution.

The soil used for the preparation of mud mortar, and the water used in the construction should be free from harmful salts. Concrete made of cement, surkhi, sand and brick ballast and mortar of cement, surkhi and sand for laying bricks is suggested to be used for all foundations in effected areas. The surkhi to be made from slightly under-burnt bricks and finely powered, mixed with about 15 to 20 per cent of cement.

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Uses of Bricks

Uses of Bricks

Some of the different uses of bricks are as follows,

1 The first class and second class bricks are used for permanent structures. These structures include, buildings, dams, roads, bridge piers, etc.,

2. The first class bricks are also used for architectural effects on structures.

3. If second class bricks are used., the surface should be plastered evenly because of the irregular size and shape of bricks.

4. The third class or sun-dried bricks are used only for temporary structures and these bricks should be avoided where heavy dampness and frequent rain is predominant.

5. The fourth class bricks are used as aggregate for foundation concrete and road metal works.

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Reinforced Brick Masonry

Reinforced Brick Masonry

Brick work strengthened by introduction of mild steel flats, hoop iron, expanded mesh or bars is termed as reinforced brick masonry. This reinforced brick masonry is capable of resisting both compressive as well as tensile and shear stress. On account of its ability to resist lateral forces, reinforced brick masonry is extensively used in seismic areas. It is essential to use first class bricks (having crushing strength of 140 kg/sq. cm or more) and rich and dense cement mortar in the reinforced brick work. The reinforcement should be effectively bedded and surrounded with mortar cover of 15 to 25 cm. This is necessary to protect the reinforcement against corrosion.

Reinforced Brick Masonry

As a matter of practice half brick walls are invariably reinforced by providing 6 to 8 mm dia bars or hoop iron (less than 8 mm in thickness) at every third or fourth course. Construction of reinforced brick lintels and roof/floor slabs is also quite common.

Reinforced brick masonry is frequently adopted for the construct ion of retaining walls especially in places where exposed brick work is necessary from architectural considerations. It is seen (hat reinforced brick retaining wall upto 4m height works out to be cheaper as compared with R.C.C. retaining walls. Such a wall is made by using special bricks (having grooves for accommodating reinforcing bars) in cement mortar 1 : 3 and reinforced with vertical MS rounds placed near each face. Horizontal reinforcement in the form of steel meshed strips are also provided at every third or fourth course.

Reinforced Brick Column

Construction of reinforced brick column is more or less similar to that of reinforced brick wall except that the horizontal steel mesh is replaced by stirrups.

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Dimensions or Size of Bricks

Dimensions or Size of Bricks

The bricks are prepared in various sizes. The custom in the locality is the governing factor for deciding the dimensions or size of bricks. Such bricks which are not standardized are known as the traditional bricks.

If bricks are large, it is difficult to burn them properly and they become too heavy to be placed with a single hand. On the other hand, if bricks are small. more quantity of mortar is required.

For India, a brick of standard size 190 mm x 90 mm x 90 mm is recommended by the BIS. With mortar thickness, the size of such a brick becomes 200 mm x 100 mm x 100 mm and it is known as the nominal size of the modular brick. Thus the nominal size of brick includes the mortar thickness.

It is found that the weight of 1 cu.m of brick earth is about 18 kN. Hence the average weight of a brick will be about 30 to 35 N.

Hence these are the dimensions or size of bricks.

Classification of Bricks

Classification of Bricks

The classification of bricks is as follows:

(i) unburnt or sun-dried bricks; and
(ii) burnt bricks.

The unburnt or sun-dried bricks are those bricks which are  dried with the help of heat that is received from sun after the process of moulding. The unburnt bricks can only be used in the construction of  simple temporary and cheap structures. Unburnt bricks should not be used at places exposed to heavy rains.

The bricks used in construction works are burnt bricks and they are classified into the following four categories:

(1) First class bricks

(2) Second class bricks

(3) Third class bricks

(4) Fourth class bricks.

(1) First class bricks:

These first class bricks are table moulded and of uniform  shape and they are burnt in kilns. The surfaces and edges of the bricks are sharp, square, smooth and straight. They comply with all the qualities of good bricks. These bricks are used for important work of permanent nature.

(2) Second class bricks:

The second class bricks are ground moulded and they are burnt in kilns. The surface of the second class bricks is slightly rough and shape is also slightly regular. These bricks may have hair cracks and their edges may not be sharp and uniform. These bricks are commonly used at places where brickwork is to be provided with a coat of plaster.

(3) Third class bricks:

These bricks are ground-moulded and they are burnt in clamps. These bricks are not very hard and they have rough surfaces with irregular and blunt edges. These bricks give dull sound when they are struck together. They are used for unimportant works, temporary structures and at places where rainfall is not heavy.

(4) Fourth class bricks:

These are overburnt bricks with irregular shape and dark colour. These bricks are used as aggregate for concrete in foundations, brick floors, surkhi, roads, etc. because of the fact that the overburnt bricks have a compact structure and hence they are sometimes found to be stronger than even the first class bricks. It is thus seen that the above classification of bricks is based on the of manufacturing or preparing bricks.

Test for Bricks

Test for Bricks

A brick is generally subjected to the following tests to find for the construction work,

(1) Absorption

(2) Crushing strength

(3) Hardness

(4) Presence of soluble salts

(5) Shape and size

(6) Soundness

(7) Structure

 

(1) Absorption:

A brick is taken and it is weighed dry. It is then immersed in water for a period of 16 hours. It is weighed again and the difference in weight indicates the amount of water absorbed by the brick. It should not in exceed 20 per cent of weight of dry brick.

(2) Compressive/Crushing strength of Bricks:

The crushing strength of a brick is found out by placing it in a compression testing machine. It is pressed till it breaks. As per BIS: 1077-1957, the minimum crushing or compressive strength of bricks is 3.50 N/mm2. The bricks with crushing strength of 7 to 14 N/mm2 are graded as A and those having above 14 N/mm2 are graded. as AA.

Test for Bricks

(3) Hardness test on bricks:

In this test, a scratch is made on brick surface with the help of a finger nail. If no impression is left on the surface, the brick is r sufficiently hard.

(4) Presence of soluble salts:

The soluble salts, if present in cause efflorescence in brick work. For finding out the presence of soluble salts in a brick, it is immersed in water for 24 hours. It is then taken out and allowed to dry in shade. The absence of grey or white deposits on indicates absence of soluble salts.

If the white deposits cover about 10 per cent surface, the efflorescence is said to be slight and it is considered as moderate, when the white deposits cover about 50 per cent of surface. If grey or white deposits are found on more than 50 per cent of surface, the efflorescence becomes heavy and it is treated as serious, when such deposits are converted into powdery mass.

(5) Shape and size:

In this test, a brick is closely inspected. It should be of standard size and its shape should be truly rectangular with sharp edges. For this purpose, 20 bricks of standard size (190 mm x 90 mm x 90 mm) are selected at random and they are stacked lengthwise, along the width and along the height.

For good quality bricks, the results should be within the following permissible limits

(6) Soundness test on brick:

In this test, the two bricks are taken and they are struck with each other. The bricks should not break and a clear ringing sound should be produced.

(7) Structure of a brick:

A brick is broken and its structure is examined. It should be homogeneous, compact and free from any defects such as holes, lumps, etc.

Types of Brick Bonds

Types of Brick Bonds

Some of the different types of brick bonds are,

1. English bond,

2. Flemish bond,

3. Stretching bond,

4. Heading bond,

5. Garden wall bond,

6. Facing bond,

7. Raking bond,

8. Dutch bond,

9. English cross-bond,

10. Zig-Zag bond,

11. Silverlock’s bond.

For English and Flemish bond refer in our website.

3. Stretching bond:

In this arrangement of bonding, all the bricks are laid as stretchers. The overlap, which is usually of half brick, is obtained by commencing each alternate course with a half brick bat. Stretching bond is used for half brick wall only. This bond is also termed as running bond and is commonly adopted in the construction of half brick thick leaves of cavity walls, partition walls, etc. Since there are no headers, suitable reinforcement should be used for structural bond.

Stretching Bond

4. Heading bond :

In this type of bonding all the bricks are laid as headers on the faces. The overlap, which is usually-of half the width of the brick is obtained by introducing a three-quarter bat in each alternate course at quoins. This bond permits better alignment and  as such it is used for walls curved on plan. This bond is chiefly used for footings in foundations for better transverse distribution of load.

Heading Bond

5.Garden wall bond:

This type of bond is suitably adopted for one brick thick wall which may act as a garden wall or a boundary wall. In garden wall bond, it is possible to build uniform faces for a wall without much labour or expense. This type of bond is not so strong as English bond and its use is restricted to the construction of dwarf walls or other similar types of walls which are not subjected to large stresses. On accounts of its good appearance, this bond is sometimes used for the construction of the outer leaves of cavity walls.

There are two types of garden wall bond,

(a) English garden wall bond
(b) Flemish garden wall bond

(a) English garden wall bond. The general arrangement of bricks in this type of bonding is similar to that of English bond except that the heading courses are only inserted at every fourth or sixth course. Usually the arrangement consists of one course of headers to three courses of stretchers. A queen closer is placed next to the quoin header of the heading course to give the necessary lap.

English garden wall bond

(b) Flemish garden wall bond. This consists of alternate course composed of one header to three or sometimes even five stretchers in series throughout the length of the courses. Each alternate course contains a three quarter bat placed next to the quoin header and a header is laid over the middle of each central stretcher.

Flemish Garden wall bond

6.Facing bond:

This arrangement of bricks is adopted for thick walls, where the facing and backing are desired to be constructed with bricks of different thickness. This bond consists of heading and stretching courses so arranged that one heading course comes after several stretching courses. Since the number of joints in the backing and the facing differ greatly, the load distribution is not uniform. This may sometimes lead to unequal settlement of the two thickness of the wall.

7.Raking bond:

This is a bond in brick work in which the bonding bricks are laid at any angle other than zero or ninety degrees. This arrangement helps to increase the longitudinal stability of thick walls built in English bond. In this arrangement of bonding, the space between the external stretchers of a wall is filled with bricks inclined to the face of the wall. This bond is introduced at certain intervals along the height of a wall.

There arc two common forms of raking bond ;
(a) Herring hone bond
(b) Diagonal bond.

(a) Herring-bone bond. This type of bond is best suited for very thick walls usually not less than four bricks thick. In this arrangement of brick work, bricks are laid in course inclined at 45° in two directions from the centre. This bond is also commonly used for brick pavings.

Herring-bone bond

(b) Diagonal bond. This bond is best suited for walls which are 2 to 4 brick thick. This bond is usually introduced at every fifth or seventh course along the height of the wall. In this bond, the bricks arc placed end to end in such a way that extreme corners of the series remain in contact with the stretchers.

Diagonal Bond

8.Dutch bond:

This bond is a modification of the old English cross bond and consists of alternate courses of headers and stretchers. In this arrangement of brick work, each stretching course starts at the quoin with a three-quarter bat and every alternate stretching course has a header placed next to the three-quarter brick bat provided at the quoin.

Dutch Bond

9.English cross-bond:

This is similar to English bond and consists of alternate course of headers and stretchers. However, in this bond, queen closer are introduced next to quoin headers and each alternate stretching course has header placed next to quoin stretcher. This bond is sufficiently strong and bears a good elevation.

English Cross Bond

10. Zig-Zag bond:

This is similar to herring-bone bond with the only difference that in this case the bricks are laid in a zig-zag fashion. This is commonly adopted in brick paved flooring.

Zig zag bond

11. Silverlock’s bond:

This is a form of bonding brick-work in which bricks are laid on edge. It is economical but weak in strength and hence it is only recommended for garden walls or partition walls. In this bond, the bricks are laid as headers and stretchers in alternate courses in such a way that headers are laid on bed aid the stretchers are laid on edge forming a continuous cavity.

Flemish Bond – Brick Masonry

Flemish Bond – Types of Flemish Bond

In Flemish bond, each course consists of alternate headers and stretchers. The alternate headers of each course are centered over the stretchers in the course below. Every alternate course starts with a header at the corner. For the breaking of vertical joints in the successive courses, closers are inserted in alternate courses next to the quoin header. In walls having their thickness equal to odd number of half bricks, bats are essentially used to achieve the bond.

Flemish bond is further divided into two different types namely,

1. Single Flemish bond,

2. Double Flemish bond.

Flemish Bond

1. Single Flemish Bond.

This bond is a combination of English bond and Flemish bond.  In this work the facing of the wall consists of Flemish bond and the backing consists of English bond in each course. This type of bonding cannot be adopted in walls less than one and a half brick in thickness. This bond is adopted to present the attractive appearance of Flemish bond with an effort to ensure full strength in the brick work.

2. Double Flemish bond.

In Double Flemish Bond, each course presents the same appearance both in the front and back elevations. Every course consists of headers and stretchers laid alternately. This type of bond is best suited from considerations of economy and appearance. It enables the one brick wall to have flush  and uniform faces on both the sides. This type of bonding is comparatively weaker than English bond.

English Bond – Brick Masonry

English Bond

English bond consists of alternate course of headers and stretches. In this English bond arrangement, vertical joints in the header courses come over each other and the vertical joints in the stretcher course are also in the same line. For the breaking of vertical joints in the successive course it is essential to place queen closer, after the first header in each heading course. The following additional points should be noted in English bond construction:

(1) In English bond, a heading course should never start with a queen closer as it is liable to get displaced in this position.

(2) In the stretcher course, the stretchers should have a minimum lap of 1/4th their length over the headers.

(3) Walls having their thickness equal to an even number of half bricks, i.e., one brick thick wail, 2 brick thick wall, 3 brick thick wall and so on, present the same appearance on both the faces, i .e. a course consisting of headers on front face will show headers on the back face also.

Isometric view of  1½ brick wall in English bond is shown below,

English bond

(4) In walls having their thickness equal to an odd number of half brick, i.e. 1½ brick thick walls or 2½ brick thick walls and so on, the same course will show stretchers on one face and headers on the other.

(5) In thick walls the middle portion is entirely filled with header to prevent the formation of vertical joints in the body of the wall.

(6) Since the number of vertical joints in the header course is twice the number of joints in the stretcher course, the joints in the header course are made thinner than those in the stretcher course.

Surkhi

Surkhi

Surkhi is called as Trass, or brick-dust in England.

Surkhi is used as a substitute for sand for concrete and mortar, and has almost the same function as of sand but it also imparts some strength and hydraulicity. Surkhi is made by grinding to powder burnt bricks, brick-bats or burnt clay ; under-burnt or over-burnt bricks should not be used, nor bricks containing high proportion of sand. When clay is especially burnt for making into surkhi, an addition of 10 to 20 per cent of quick lime will improve its quality ; small clay balls are made for burning.

Surkhi for plaster may be made from slightly under-burnt bricks, and ground very fine ; this will improve the hydraulicity of fat lime. Surkhi must be well mixed with lime, preferably in a mortar-mill. (Test for under- burnt bricks is that they should not dissolve in water). Surkhi mortar gains strength if left immersed in water. Surkhi is not suitable for plaster exposed to weathering and humid conditions.

Pozzolana—Is a volcanic substance found in a number of places but named from the deposits at Pozzuoli near Naples in Italy. It is mixed with lime to produce mortar. It is manufactured artificially in India by burning some types of clays and grinding it very fine. It is more or less like Surkhi. It can be used in all situations where surkhi can be used to give superior performance.

Surkhi

Surkhi mixed with lime and water. A weathering coarse.

Surkhi makes cement mortars and concretes more water proof, more resistant to alkalies and to salt solutions than those in which no surkhi is used. Surkhi mixed in cement concrete has been used in some of the big dams and other massive works in India. This admixture is known to reduce the temperature rise during hydration in a mass cement concrete and reduce cracking. It is also useful in sea-water construction, in structures which are subject to attack from aggressive ground waters or industrial waters, and in hydraulic structures where water tightness is the first consideration. Surkhi mixed cement concrete is more plastic, bleeds less and segregates less as compared to ordinary cement concrete. A surkhi concrete of 25 to 50 mm slump is just as readily placed as a corresponding straight cement of much higher slum. The proportion of surkhi recommended is 10 to 30 per cent of cement (cement will be proportionately less) but it must be ground as fine as the cement. Surkhi should riot be added to aluminous cements. Surkhi is added both in mortar and concrete. The addition of surkhi is accompanied by slight reduction in strength as surkhi attains its full strength only after one year. Surkhi concrete is subject to a slightly higher shrinkage than ordinary concrete. Surkhi is not a standerdized produce and its properties are widely variable.