The bricks are obtained by moulding clay in the regular rectangular mould. These blocks are dried and then burnt to get pucca bricks ready to use in masonry works. The construction carried out using bricks and mortar is known as Brick Masonry. Mud Mortar, Lime Mortar and Cement Mortar may be used in brick masonry. Type of mortar to be used in brick masonry depends upon the strength of the work required.
Types of units:
There are several types of units are available:
- Burnt clay building bricks
- Stone (in regular sized units)
- Sand-lime bricks
- Fly ash bricks
- Concrete blocks (solid & hollow)
- Autoclaved cellular concrete blocks etc.
- Walls a) Load bearing, b) non-load bearing
- Retaining walls
Bricks & masonry units call designations are on the basis of their average compressive strength, which may range up to 40 MPa.
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Properties of units:
- Compressive strength: usually tested flat
- Absorption is related to porosity (24 hours absorption)
- Suction rate
- Moisture expansion
- Efflorescence and soluble salt content (like sodium sulphate)
- Density and thermal properties (k, c)
- Fire behaviour and resistance against chemical attack
Bricks are the most commonly used material for building walls. Bricks are made of clay, which is easily available & easy to handle. Brick masonry is made of bricks units, bonded together with mortar. Two essential components of brick masonry are – (i) Bricks & (ii) Mortar.
Mortar binds the bricks & makes them act as a homogeneous mass. High strength mortar is unnecessary, but optimal mortar choice is important for any structure. Moreover, type of structure, masonry unit & their strength, Exposure, environment etc governs the mortar selection. Following types of mortars are used: (a) Cement mortar, (b) Lime mortar, (c) Mud mortar, (d) Cement-Lime mortar & (e) Lime-Surkhi mortar.
Mortars may also be used as cement-sand mortar, cement-lime-sand mortar, Lime-pozzolana-sand mortar etc. Cement mortar is used for high-rise building, where strength is of prime importance. In other hands, Mud mortar is used only for the low-rise building which carries a light load. Lime mortar & Lime Surkhi mortars are used for all types of construction. The strength of brickwork is much lower than that of the unit, which depends on unit strength as well as joints.
Mortars are also classified as H1, H2, M1, M2, M3, L1, L2 etc on the basis of their 28 days compressive strength. The strength is ranging from 10 MPa for H1 to 0.5 MPa for L2.
Properties of Mortar:
- Strength: A strong mortar will have high crushing, tensile & shear strength.
- Workability: Workable mortar spreads easily & must set early enough for work to progress at the same time should not stiffen.
- By retaining water and not losing it to brick stiffening is avoided and also enables better bond & better resistance against rain penetration.
- Low drying shrinkage & adequate strength (lime-cement-sand mortar).
- Resistance to rain penetration (low porosity and good bond at the joint) & durability (sulphates in brick, salt crystallization) are other important properties.
Additives for mortar:
- Water-proofing compound
- Water reducing compound (Ex. plasticizer)
- Air entraining agents
Brick masonry has been found in the ancient ruins of Harappa & Mahenjo-Daro, dating back to around 2500 BC. Bricks are manufactured by moulding clay in rectangular blocks of uniform predetermined size, drying them & then burning them in a kiln. The strength of brick masonry depends upon – (i) Quality of bricks, (ii) Quality of mortar & (iii) Method of bonding used. Unbonded wall, even constructed with good quality bricks & good quality mortar has little strength & stability.
Brick masonry is sometimes preferred over other types of masonry due to the following reasons:
- All the bricks are of uniform size & shape, and hence they can be laid in any definite pattern.
- Brick units are light in unit & small in size. Hence these can be easily handled by bricks layers by hand.
- Brick does not need any dressing.
- The art of brick lying can be understood very easily, and even unskilled masons can construct brick masonry.
- Bricks are easily available everywhere, so not require transportation from long distance.
- Ornamental works can be easily done with bricks.
- Light partition walls & filler walls can be easily constructed.
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A number of terms are generally used here.
Stretcher: It is the longer face of the brick (190 x 90mm) as seen in the elevation of the wall. If a course of bricks contains any stretchers on facing is known as a stretcher course or stretching course.
Header: It is the shorter face of the brick (90 x 90mm) – Header course.
Lap: It is the horizontal distance between the vertical joints of the successive brick course.
Perpend: It is an imaginary vertical line which includes the vertical joints separating two adjoining bricks.
Bed: Bed is the lower surface (190 x 90mm) of the brick which when laid flat.
Bed Joint: It is the horizontal layer of mortar over which bricks are laid flat.
Arises: It is the edge of a brick.
Quoin: It is the corner or an external angle on the face side of a wall. Generally, quoins are at right angles, sometimes >900 also.
Closer: It is a portion of brick with the cut made longitudinally, and is used to close up bond at the end of the course. Various types of closer given below:
- Queen Closer: It is a brick which is half as wide as the full brick, also known as queen closer half if broken into two pieces, known as queen closer quarter.
- King Closer: It is the brick in which the corner is cut so as to get half header & half stretcher adjacent faces.
- Bevelled Closer: This is obtained by cutting a triangular portion of half the width but of full length.
- Mitred Closer: It is the brick in which one end is splayed/ mitred. The angle of splay may vary from 450 to 600.
Bat: It is the portion of brick cut across the width. The length of the brick-bat may be half or 3/4th of the original brick.
Bullnose: Specially moulded bricks with one edge rounded (single bullnose) or with two edges rounded (double bullnose). These are used in copings or in such portions where rounded course are preferred to sharp arises.
Splays: These are specially moulded bricks which are often used to form plinth.
Dogleg or Angle: Used to ensure a satisfactory bond at quoins which are at an angle other than the right angle. The angle & length of the faces forming the dog-leg varies according to requirements. These are preferred to Mitred closer.
Frog or kick: It is an indentation in the face of a brick to form a key for holding the mortar. When the frog is only on one face, that brick is laid with that face on the top. Sometimes, frogs are provided on both faces. However, no frogs are provided in wire-cut bricks. A pressed brick has two frogs (as a rule) & a hand-made brick has only one frog.
Racking Back: At the end of a day’s work, a wall is terminated in a stepped manner. This is known as racking back.
Toothing: It is the termination of a wall in such a method that each alternate course at the end projects, in order to provide adequate bond if the wall is continuous horizontally at a later stage.
Bonds: Under load, the units shall act jointly; the most important rule is that the vertical cross joints in any course shall be staggered & should not be nearer than a quarter of brick length from those in a course below or above.
Bond in Brick Work:
It is the method of arranging the bricks in a course so that:
- The individual bricks are joined together;
- Vertical joints of the successive courses do not lie in the same vertical line so as to ensure distribution of load on lower courses; and
- An artistic effect is created when the brickwork is left unplastered.
Brick used in masonry should be all of the uniform sizes. If they are not bonded & arranged properly, continuous vertical joints will result & forming an unbounded wall which produces less strength & stability.
Rules for Bonding:
- The bricks should be of uniform shape & size. The length of the brick should be twice its width plus one joint, so that uniform lap is obtained.
- The lap should be at least 1/4th brick along the length & ½ brick across & thick of wall.
- Use of brick-bats should be avoided, except in special cases.
- In alternate courses, the centre line of the header should coincide with the centre line of the stretcher, in the course below or above it.
- The vertical joint in the alternate courses should be along the same perpend.
- Stretcher should be used on the facing only, while hearting should be in headers only.
- Every sixth course on both faces of the wall should be a header course.
Types of Bonds:
- Stretcher Bond: All the bricks are arranged in stretcher courses. However, care is taken to break the vertical joint by using brick-bats. This type of construction is used in partition walls, sleeper walls, division walls or chimney stacks which are half-brick thick.
- Header Bond: All bricks are arranged in header courses. This type of bond is useful for the construction of one brick thick walls. It is unsuitable for load-bearing walls due to less strength but used in the construction of footings.
- English Bond: In this type of bond, alternate courses consist of headers & stretchers. This is the strongest bond and is, thus commonly used for walls of all thickness. To break the continuity of vertical joints, a queen closer is used at the beginning & end of a wall after the first header.
- Flemish Bond: In this, each course comprises alternate header & stretcher. Alternate courses start with stretcher & header. To break vertical joints, queen closer is used if the courses start with a header. Every header is centrally supported on the stretcher below it.
- Double Flemish Bond: In case of a double Flemish bond, both faces of the wall have a Flemish look, i.e. each course consists of alternate header & stretcher.
- Single Flemish Bond: In case of a single Flemish bond, outer faces of the wall have a Flemish look, whereas the inner faces have the English bond look. The disadvantage of the single Flemish bond is that it cannot be used for walls of thickness less than 1⅟₂ brick and in some portions, long vertical joints are unavoidable. Construction of Flemish bond needs great skill. It gives a good appearance but it is not as strong in English bond. Flemish bond may be used to get a good aesthetic look if only pointing is to be used for the finished wall.
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Comparison between English bond & Flemish bond: –
- English bond is stronger than Flemish bond for wall thicker than 1⅟₂ brick.
- Flemish bond gives a better appearance than the English bond.
- A large no. of brick-bats can be used in Flemish bond; however, more mortar is required.
- A fairly uniform is obtained on both sides of a one brick wall in Flemish bond.
- Construction with Flemish bond requires greater skill in comparison to English bond.
- English Cross Bond: This is a modification of English bond, used to improve the appearance of the work. This bond combines the requirement of beauty & strength. Special features are: – Alternate courses of header & stretcher are providing as in English bond. Queen closer are placed next to quoin header. A header is introduced next to the quoin structure in every alternate structure course.
- Dutch Bond: Another modified form of English bond. In this bond, the corner of the wall is strengthened. Special features are: – an alternate course of header & stretcher is provide as in English bond. Every stretcher course starts at the quoin with a three-quarter bat. In every alternate structure course, a header is placed next to the three quarter brick bat provide at the quoin.
- Raking Bond: Used in the very thick wall, which reduces the longitudinal stiffness of the wall. Special features are: – The bricks are arranged in an inclined direction, in the space between the external structures of the wall. The raking or inclination should be an opposite direction in alternate courses of raking bond. The raking bond is not provided in successive courses. It is provide at a regular internal of four to eight courses in the height of the wall. The raking course is generally provided between the two structure courses of the wall having thick equal to even multiple of half bricks, to make the bond more effective. It has two types:
- Diagonal Bond: Bricks are arranged at 450 in such a way that extreme corners of the series remain in contact with the external line of the structure. Bricks need to be cut into triangular shape to pack small triangular spaces at the ends. The bond is best suited for walls which are 2 to 4 brick thick. Diagonal bond are provided at every fifth or seven courses in a wall.
- Herring bone Bond: It is provided at every six or eight course, if the thick of the wall is more than 4 bricks. Bricks are arranged at 450 in two opposite direction from the centre of the wall thick. The bond is also used for an ornamental finish to the face work, & also for brick flooring.
- Garden wall Bond: It is used for the construction of compound wall, garden wall, boundary wall, which are usually one-brick thick & height does not exceed two meters. It is not as strong as English bond but is more attractive; used sometimes in the construction of outer leaves of cavity walls for this. Three types:
- English garden wall bond: It consists one course of header after 3 or 5 courses of stretchers. In each header course, a queen closer is placed next to quoin header & in stretcher courses, quoin header are placed in alternate courses.
- Flemish garden wall bond: Each course content one header after 3 to 5 stretcher continuous placed. Each alternate course contains a ¾ thick brick bat placed next to the quoin header, & a header lay over the middle of each central structure. This bond is also known as the Scotch bond or Sussex bond.
- Garden wall Monk Bond: Special type of Flemish Garden wall bond where each courses contains one header after two successive stretchers. Every alternate course contains a quoin header followed by a ¾ brick bat. Due to this, the header rest over the joint between two successive stretchers.
- Zig-zag Bond: This is similar to herring bone bond except that the bricks are laid in a zigzag manner. This is commonly used for making ornamental panels in the brick flooring.
- Facing bond: If bricks of different sizes are to be used on facing & backing, facing bond is chosen. In this, a one header course is provided after several stretcher courses. The distance between the successive header courses is equal to the least common multiplier of the thick of backing & facing bricks. For example, if facing bricks are 100 mm thick & backing bricks are 75mm thick, the header course will be 300 mm apart.
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