As per the old convention, masonry is a term used to indicate the art of building structures in stones using mortar and stone. But in a simplified form, it may be defined as construction of building units bonded together with mortar. The building units may be brick, stone, concrete, hollow blocks, etc.
The selection of the type of unit for the masonry is made keeping in view the requirements of strength, water proofing, thermal insulation, fire resistance, durability and economy. The binding strength of the mortar is usually disregarded as far as the strength of masonry is concerned.
The mortar is required to keep the building units in position. It is prepared by mixing lime or cement with sand after adding water which forms the mortar. Sometimes a portion of cement is replaced by lime and accordingly called as cement-lime mortar. If the mortar is to be strong, more plastic and workable lime-cement mortar is used.
The masonry is classified based on the basic unit used for the structure.
16.2 BRICK MASONRY
As bricks are comparatively small in size, they can be handled easily. Further, brick being uniform in size can be arranged systematically and bonded together with mortar to form a homogeneous mass, which is called brick masonry. The materials used for brick masonry are bricks, mortar and specially shaped bricks. Mortar helps to bind the individual bricks and to form a cushion to take up the inequalities in the brick and to distribute the pressure evenly and also to fill up the interstices in the bricks.
Some of the terms which are used in brick masonry are defined below.
A brick laid with its breadth or width parallel to the face or direction of a wall.
A brick laid with its length parallel to the face or direction of the wall.
The lower surface of a brick when laid flat.
A portion of a brick cut across the width.
A part of brick that is used to close up the bond at the end of brick course. The different closers are: (i) king closer, (ii) queen closer and (iii) bevelled closer.
A corner of the external angle on the face side of a wall.
A brick cut to a special shape and used at oblique quoins.
Figure 16.1 shows courses of brickwork and Fig. 16.2 shows types of special bricks.
Figure 16.1 Courses of brickwork
Figure 16.2 Types of bricks
16.2.2 Brick Laying Tools
Main tools used for brick laying are trowel, plumb bob, bolster, tri-square, lime and pins, sprit level, and brick hammer. Figure 16.3 shows the above tools and is explained below.
Figure 16.3 Common brick laying tools
Brick trowel is usually about 30 cm long with a steel blade and a handle. The blade has one straight edge and one end curved edge.
It is used to set out a right-angled corner. It is like a large triangle having two legs. It should be used carefully to set the first course.
3. Plumb Bob
It consists of a piece of thick straight wood ruler with a piece of string which is fixed in the wood at one end and the metal plumb bob at the other end.
4. Line and Pins
The two pins used for brickwork have flattened and blunt point ends for inserting into the joints of brickwork as work proceeds.
5. Sprit Level
It is used to level the brickwork. It consists of a hardwood stock with anything from two to six bubbles. These bubbles are small, sealed inside a glass tube.
6. Brick Hammer and Bolster
Cutting of bricks to provide suitable shapes for the bonding is done with the club hammer and bolster.
16.2.3 Materials Used
Bricks and mortar are the materials used. Bricks may be of first, second, third or fourth class depending on the type of work.
As a general rule, the strength of a mortar need not be more than that of the bricks. Plasters should be more plastic and made of fine sand. Sand for mortar should pass through 64 mesh and for plaster 12 mesh. Table 16.1 gives the recommended mortars for different brick strengths.
Table 16.1 Recommended mortars for brickwork
Combination mortar is more plastic than cement mortar. For low-strength bricks, mortars of low strengths as given below may be used.
Cement and sand mortar 1:8; Lime, surki and sand mortar 1:2:6
Lime and sand mortar 1:3; Cement, lime, surki and sand mortar 1:2:4:20
Cement, lime and sand mortar 1:4:14
16.2.4 Bonds in Brickwork
It is the process of arranging bricks in courses to ensure that vertical joints do not come one over the other. A wall built without any continuous vertical joint shall distribute the load properly and shall also be more strong and durable.
1. Stretcher Band
In this type of bond, all courses are laid as stretchers. As only stretchers are visible in elevation, this bond is referred to as stretcher bond. This is used for partition walls (Fig. 16.4(a)).
2. Header Bond
In this type of bond, all courses are laid as headers. As only headers are visible in elevation, this bond is referred to as header bond. This is used for one brick and curved walls (Fig. 16.4(b)).
Figure 16.4 Bonds in brickwork
3. English Bond
This bond is produced by laying alternate courses of stretchers and headers. In order to break the joints vertically, it is essential to use a closer after the header quoin in the heading course. This is the most commonly used bond which is also the strongest. This type of bond is used for walls carrying heavy loads. Figure 16.4(c) shows formation of a wall adopting English bond.
4. Flemish Bond
This bond is produced by laying alternate stretchers and headers in each course. The headers and stretchers appear in the same course alternately on the front and the faces. The queen closer is used next to the quoin header in alternate courses in order to break the continuity of the vertical joints. A header in any course is in the centre of a stretcher in the course above or below it. This bond is also used for walls to carry moderate loads. Figure 16.4(d) shows formation of wall adopting Flemish bond.
16.2.5 Comparison of English and Flemish Bonds
Table 16.2 gives a comparison of English and Flemish bonds.
Table 16.2 Comparison of English and Flemish bond
16.2.6 General Principles of Construction of Brick Masonry
Brickwork should be systematically done keeping in view the bonding, jointing and finishing. The laying of brick masonry is practically the same for all types of constructions. But some special considerations have to be given to each case. Mortar of 10 cm thickness is first spread.
Bricks soaked in water (so as to prevent absorption of moisture from the mortar) are placed over the mortar and pressed to ensure adequate adhesion. Both the longitudinal and cross joints are packed well with mortar. Proper bond is adopted and the brickwork is to be constructed in uniform layers. It is essential to check frequently the verticality of the walls and perpendicularity between the walls. The joints which are exposed are carefully finished by jointing or painting. At the end of a day’s work, the brickwork is raked back by stepping the brickwork. After construction, brickwork should be kept wet for two weeks. The following points should be observed while supervising the construction of brick masonry:
- Bricks should conform to the specification and requirements of the work.
- Bricks should be saturated well with water before use.
- Bricks should be laid with frog upwards, with mortar completely covering the bed.
- A suitable bond has to be used to avoid continuous vertical joints anywhere in the work.
- A good quality mortar has to be used and the thickness of mortar should not be more than 10 mm.
- The brickwork should be raised uniformly.
- Brickbats should be minimised and to be used only in the required places.
- In no case the height of masonry should be greater than 1 m in a day’s work.
- All vertical faces should be checked with a plumb bob and wall junctions should be checked for perpendicularity.
- After the construction is over, the brickwork should be watered well for two weeks.
16.3 Stone Masonry
Stones are abundantly available in nature which can be properly shaped and used for construction of various parts of a building. Similar to brick masonry, stones also can be systematically arranged to form a homogeneous mass called stone masonry. The materials used for stone masonry are stones and mortar. The common types of stones used for stone masonry in India are: granites, sandstones, limestones, marbles and slates. Stone masonry is strong and durable.
Apart from the use in building construction, stones are used for structures like dams, piers, waterfront works, monuments and memorials. Stone masonry is not affected by dampness and does not require plastering. However, it will be cheap only in areas where it is abundantly available.
1. Bed Surface
Surface of a stone perpendicular to the line of pressure.
2. String Course
A horizontal course of masonry continuously projecting from the face of the wall.
A stone embedded in a wall to support a structural member.
A moulded projection of masonry on the top of a wall.
5. Through Stone
Stone extending throughout the thickness of the wall.
A filled-up core of a rubble wall.
A masonry portion forming the side of an opening.
16.3.2 Materials Used
Materials used for stone masonry are stones and mortar. Common types of stones which are used for stone masonry along with their crushing strength are presented in Table 16.3.
Table 16.3 Common types of stones used for stone necessary
Generally lime and cement mortars are used for stone masonry. Their function is to initially provide a workable matrix and ultimately a hard-binding material, which renders masonry into a monolithic unit. Hydraulic lime and Portland cement with river sand are used.
16.3.3 Cutting and Dressing of Stones
Dressing is the art of cutting the stones to shape required for use in structures. A brief discussion on dressing and purpose of dressing is made in Section 2.8.
Tools used for cutting and dressing stones is given in Fig. 16.5.
Figure 16.5 Tools for cutting and dressing stones
Stones for two major types of stone masonry, viz., rubble and ashlar masonry (discussed in Section 16.3.4) are dressed as follows.
1. Dressing for Rubble Masonry
- For this type of masonry, stones are shaped by means of hammer. Lower and upper surfaces of stones are almost dressed flat.
- For this type of masonry, stones which have front face almost rectangular and remaining irregular are also used.
2. Dressing for Ashlar Masonry
- For this type of masonry, the faces of stones are finely dressed by means of chisels.
- Further, chiselled faces are sometimes rubbed to give a smooth surface in case of special works like monumental works.
Different types of surface finishes adopted are presented in Fig. 16.6.
- Rough tooled surface
- Tooled surface
- Cut stone surface
- Hammer dressed surface
- Polished surface
- Rubbed surface
Figure 16.6 Types of surface finishes
16.3.4 Types of Stone Masonry
Stone masonry is classified based on the thickness of joints, continuity of courses and finish of face. Rubble Masonry and Ashlar Masonry are discussed below (IS: 1597, Parts 1 and 2, 1992).
1. Rubble Masonry
Rubble masonry is a stonework wherein blocks of stones are either undressed or roughly dressed and have wider joints. The stones used are not of uniform size and shape but generally of pyramidal in shape to some extent. Vertical and transverse bonds have to be attained. Through stones are provided from back to the face of wall to ensure better bonding. The strength of this masonry depends on the quality of mortar, use of through stones and filling of spaces. There are different types of rubble masonry, viz., random rubble, squared rubble and polygonal rubble. Figure 16.7 shows the various types of rubble masonry.
Figure 16.7 Types of rubble masonry
2. Ashlar Masonry
Ashlar masonry is a stonework wherein blocks of stones are accurately dressed with very fine joints of 3 mm thickness. It is essential to ensure that the sizes of individual stones are in conformity with the general properties of the wall. In this masonry the beds, sides and faces are finely chisel dressed. The backing of such walls may be rubble or ashlar masonry. It is the highest grade of masonry and costly. There are different types of ashlar masonry, viz., ashlar fine, ashlar rough tooled, ashlar rock or quarry faced, ashlar chamfered and ashlar facing. Figure 16.8 shows some of the types of ashlar masonry.
Figure 16.8 Types of ashlar masonry
3. Sub-divisions of Rubble and Ashlar Masonry
Various sub-divisions of these types are:
(i) Rubble Masonry
- Random Rubble
- Square Rubble
(iii) Built to regular courses
(ii) Ashlar Masonry
- Ashlar fine
- Ashlar rough tooled
- Ashlar rock or quarry faced
- Ashlar chamfered
- Ashlar facing
- Ashlar block-in-course
16.3.5 General Principles of Construction of Stone Masonry
The construction procedure for stone masonry is slightly different from that of brick masonry. Unlike in brick masonry, in stone masonry stones of different sizes and shapes are used and accordingly there is slight variation in construction. However, basically the requirements of vertical joints not being continuous, thickness of mortar joints and quality of mortar, verticality and perpendicularity of bonds, and the overall stability of wall are same in both. Even in stone masonry, procedures differ slightly between rubble and ashlar masonry constructions. However, the following general principles of construction should be observed while supervising the stony masonry construction:
- Stones should be hard, tough and durable.
- Pressure acting on the stone should be perpendicular to the bedding planes.
- Stone masonry work should not be designed to take any tension.
- Stones should be well watered before use.
- Through stones should be used sufficiently such that they cover about 15–25% of the area in elevation.
- Stones should be laid on its natural bed.
- Extreme care has to be taken by providing proper bond to prevent formation of vertical joints.
- Hearting of masonry should be properly packed with chips and mortar.
- Verticality of the faces of the masonry walls should be checked with a plumb rule.
- Portions of the masonry should be raised uniformly throughout its length.
- Cement mortar and sometimes rich lime mortar may be used.
- Proper dressing of stones has to be done wherever needed.
- Surfaces of the stone masonry should be kept wet while the work is in progress and also till the mortar has set.
- All laid fine dressed stonework should be protected against damage during further construction.
16.3.6 Comparison of Brick and Stone Masonry
Brick masonry and stone masonry are compared in Table 16.4.
Table 16.4 Comparison of brick and stone masonry
16.4 CONCRETE HOLLOW BLOCK MASONRY
Cement concrete hollow blocks have been in use for several masonry constructions. Several advantages have given room for rapid development and use of the same in place of traditional construction materials like stones and bricks.
Typical concrete masonry units are shown in Fig. 16.9 (Sharma, 1988), in addition to the concrete hollow blocks referred to in Chapter 9.
Figure 16.9 Typical concrete masonry units
Based on the job requirement, the concrete blocks may be made. There is no standard size of concrete blocks. However, Concrete Association of India (CAI) recommends that the face thickness should not be less than 5 cm and the net area should be atleast 55–60% of the gross area.
The common sizes for building blocks are given in Table 16.5.
Table 16.5 Common sizes of blocks
16.4.1 Use of Hollow Concrete Blocks for Masonry
Following are the uses of concrete blocks for masonry construction:
- Large in size but easy to handle
- Uniformity in design
- Easy handling and placing
- Adequate strength
- Attractive appearance
- No need of plastering for outside work
- Less number of masonry joints
- Less cost
- Easy method of manufacturing
16.4.2 Laying of Concrete Hollow Block Masonry
Different types of basic hollow blocks used in construction are discussed in Section 9.6.1. Additional hollow block units are given in Fig. 16.9 Now the construction features are explained.
1. Construction of Walls
A mortar bed is spread on the foundation concrete and levelled to have a uniform thickness everywhere. The corner block is first placed and positioned accurately. Mortar is applied to the other end and one block is positioned to the end and aligned. The level of the course is checked after placing a few blocks. If necessary, the blocks are tapped with additional mortar such that the mortar thickness is 2 cm below and on the ends. The first course is checked to be in plumb before planning second and additional courses.
As done in brick laying, the successive courses are laid in such a manner so as to break the joints vertically. For vertical joints the mortar is applied to the projection at the sides of the block. As followed for the first course, the courses are built starting from the corners only. Every time, the verticality and horizontality are checked. All the four vertical edges of the final block and the edges of the opening are covered with mortar and pushed in position. The face of the masonry may be pointed by running a tool. The type of joint recommended are weathered, V-shaped or concave, such that the joints shed off water easily.
2. Construction of Columns
Columns are used wherever a large pressure to be transferred through large bearing surface. The columns may form an integral part of the wall or it can be a separate unit. The columns are made of standard stretcher and corner blocks or other special shapes are used. For better stability, the hollows within the blocks may be filled with plain or reinforced concrete (Fig. 16.10(a)).
Figure 16.10 Pilasters and piers
3. Construction of Window and Door Openings
Blocks with hole (jamb) near the opening should be filled with concrete and wooden plugs (Fig. 16.10(b)). The door or window frames are screwed to the wooden plugs. It is also fixed in the lintel with small dowels of mild steel. Under the base of the window or door, a course of solid concrete block masonry is laid which is extended into the adjacent walls up to a distance of at least 30 cm on either side. Lintels are also of hollow channel-shaped sections which can be filled with concrete and provided with steel reinforcement at their bottom.
4. Construction of Reinforced Walls
This is made by providing vertical reinforcement in the hollow with concrete (Fig. 16.11). In order to increase the strength of the wall, reinforcement is provided at the horizontal joints. Because of this provision, expansion cracks which may occur due to moisture and change of temperature may be reduced. Further, two horizontal bars of 6 mm diameter are placed on each on the face of the wall. Instead of steel rods, welded steel mesh may be used wherever needed (Fig. 16.11).
Figure 16.11 Jamb details for 200 mm thick hollow block wall
16.4.3 Concrete Blocks with Concrete Filling
Concrete hollow blocks constructed with two through holes to form continuous vertical hole are ideal for concrete filling. These holes can be completely or partly filled with concrete during the process of construction itself. For this purpose, mixes with large size aggregates may be used. This provision will add greater strength to walls. It has been found from the tests that filling of hollow blocks with plain concrete will give basic strength approximately halfway between these for unfilled blocks and the solid blocks with the same quality of concrete.
16.4.4 Reinforced Concrete Hollow Block Masonry
In the conventional hollow block masonry, the vertical holes may be made to accommodate steel reinforcement and can thus be made of reinforced concrete construction. Similarly special concrete blocks can be made to accommodate horizontal reinforcements. Such a horizontally reinforced hollow block can be used as lintels and horizontally strengthened reinforced concrete bonds can be built up with these blocks. This type of construction is known as reinforced concrete hollow block masonry construction.
16.4.5 Special Features of Concrete Block Masonry
The important features to be incorporated, compared to regular brick masonry, are control joints, band beams and joint reinforcements. These factors are to be provided failing which the block masonry is bound to result in random cracking due to shrinkage and moisture movements. These factors are discussed below.
1. Control Joints
Concrete has higher coefficient of expansion than brickwork. In order to control thermal movements, these joints are built as continuous and vertical. Further, to minimise cutting of units, they are to be located at change of sections. These joints may be shrinkage joints and expansion joints. The shrinkage joints are continuous vertical joints approximately 18 mm thick. These joints are later raked and caulked. Expansion joints are located at spacing of 45–60 m in suitable locations. These joints are filled with joint filers, which are compressible materials that close the gap but allow movement.
2. Bond Beams
Bond beams are similar to lintels which are to be provided on top of openings or top of walls such as compound walls. This is constructed using special channel-shaped units which are reinforced and filled with concrete. It serves as a structural element as that of a lintel to control cracks on top of openings.
3. Joint Reinforcement
For crack control, horizontal joint reinforcements in the form of minimum two No. 9 gauge wires at intervals can be used. As they are expensive, they are not generally provided. When used as load-bearing walls with RCC slabs resting on the walls, the top three courses at least should be provided with joint reinforcement (Fig. 16.12).
Figure 16.12 Load-bearing wall
16.4.6 Compound Walls in Hollow Block
Compound walls are nowadays preferred to be of unplastered concrete blockwork. The construction is cheap and no maintenance is needed. There are many variations in the construction of these walls. The convenient method is to install under-reamed or cast-in-situ piles at stipulated intervals (of 3–4 m) with grade beam on top of the piles and the blockwork built on top of the grade beams.
Vertical reinforcements are provided in the hollow blocks at regular intervals from the piles. This provision strengthens the wall along its length giving lateral resistance to wing loads or earth pressure. The top of these walls are finished with a coping cast in a channel-shaped block on top (Varghese, 2012).
16.5 REINFORCED BRICK MASONRY
Ordinary brick masonry can not take tensile stresses as the mortar joints separate out and the bricks pulled out. In order to increase the load-carrying capacity, in particular tensile stresses, of ordinary brick masonry steel reinforcement is introduced in between mortar joints. This type of construction can withstand tensile and shear stresses for moderate loading.
Reinforced brick masonry is recommended in the following cases:
- When excessive compressive loads are to be supported
- When the brickwork has to withstand tensile and shear stresses
- When the supporting soil may be subjected to differential settlement
- When the brick masonry is to be provided over openings of doors, windows and passages
- When the brick masonry has to sustain lateral stress
- When it is intended to strengthen the longitudinal bond
- When constructions in earthquake-prone areas are to be made
The following points should be kept in mind:
- All the bricks should be structurally sound and of uniform size.
- In order to bond the brickwork, a cement mortar of 1: 3 should be used.
- The joints have to be constructed carefully such that the reinforcement gets sufficient cover and is also prevented from corrosion.
Typical reinforced brick masonry are discussed below.
16.5.1 Reinforced Brick Masonry Walls
Here the reinforcement may be iron base or expanded metal mash provided at every third or fourth course. Flat bars of section about 25 mm × 2 mm may be used as hoop iron reinforcement for walls. They are hooked at corners and junctions. In order to increase the resistance against rusting, the bars are dipped in tar and sanded immediately. Reinforcement in vertical direction is provided by using special bricks or blocks. Mild steel bars of 6 mm diameter may also be used as longitudinal reinforcement in walls. A detailed discussion is made in Chapter 7.
16.5.2 Reinforced Brick Masonry Columns
These columns are made with special-purpose bricks and vertical bars running through them. In order to keep the bars in position and to strengthen the brickwork, steel plates of 6 mm thick are introduced. Bent bars of small diameters of about 12 mm can be used in the horizontal joints (Fig. 16.13).
Figure 16.13 Reinforcement of brick masonry column
16.5.3 Reinforced Brick Masonry Lintel
In lintels, bars are provided longitudinally in between the vertical joints and extending from joint to joint. Further, to resist the vertical shear, additional 6 mm diameter steel stirrups may be used (Fig. 16.14).
16.5.4 Reinforced Brick Masonry Slab
Floor slabs of brickwork with reinforcement is also done. The conventional centring is made. The centring is covered with earth for a depth of about 20–25 mm and well compacted and sand sprinkled on the top.
Figure 16.14 Reinforcement in brick masonry lintels
Then the reinforcement is placed in the correct direction. The bricks are laid in one or two directions. The joints are then filled with mortar such that the reinforcement is fully closed. The work is kept moist for a period of two days and then kept fully wet for 14 days. The centring is then removed. The top and bottom surface of slab are then suitably finished (Fig. 16.15).
Figure 16.15 Slab with reinforced brickwork
- Masonry may be defined as construction of building units bonded together with mortar.
- The selection of type of unit for the masonry is made keeping in view the requirements of strength, water proofing, thermal insulation, fire resistance, durability and economy.
- The mortar is required to keep the building units in position. The binding strength of the mortar is usually disregarded as far as the strength of the masonry is concerned.
- Main types of masonry are brick masonry, stone masonry, concrete hollow block masonry and reinforced brick masonry.
- Bond is the process of arranging bricks in courses to ensure that vertical joints do not come one over the other.
- In stretcher bond all courses are laid as stretchers. As only stretchers are visible in elevation, this bond is referred to as stretcher bond.
- In header bond, all courses are laid as headers. As only headers are visible in elevation, this bond is referred to as header bond.
- English bond is produced by laying alternate courses of stretchers and headers, so as to break the joints vertically.
- Flemish bond is produced by laying alternate stretchers and headers in each course. The headers and stretchers appear in the same course alternately on the front and the back faces.
- Brickwork should be systematically done keeping in view the bonding, jointing and finishing.
- Stones also can be systematically arranged to form a homogeneous mass called stone masonry.
- Dressing is the art of cutting the stones to the shape required for use in structures.
- Stone masonry is classified based on the thickness of joints, continuity of courses and finish of face. The two major types are Rubble masonry and Ashlar masonry.
- Rubble masonry is a stonework wherein blocks of stones are either undressed or roughly dressed and have wider joints.
- Ashlar masonry is a stonework wherein blocks of stones are accurately dressed with very fine joints of 3 mm thickness.
- Cement concrete hollow blocks have been in use for several masonry constructions. Several advantages have given room for rapid development and use of the same in place of traditional construction materials like stones and bricks.
- In order to increase the load-carrying capacity, in particular tensile stresses, of ordinary brick masonry steel reinforcement is introduced in between mortar joints. Such a structure is called reinforced brick masonry.
- In reinforced brick masonry walls, iron bars or expanded metal mesh are provided at every third or fourth course.
- Reinforced brick masonry columns are made with special-purpose bricks and vertical bars running through them.
- In reinforced brick masonry lintel, bars are provided longitudinally in between the vertical joints and extending from joint to joint.
- What is meant by efflorescence in brick work? List the sources which cause efflorescence.
- How does English bond differ from Flemish bond? Explain with a neat diagram.
- Draw neat sketches, in plans of successive courses and elevation, to illustrate the construction of a brick wall, 2½ brick thick in English bond at a right-angled corner.(AMIE)
- Discuss the general principles to be observed during the construction of brick masonry work.
- What is the difference between English bond and Flemish bond in brick masonry construction?(AMIE)
- Explain with neat sketches the various types of joints used in stone masonry for placing stones together.
- Enumerate the various classes of rubble masonry.
- What are the common defects which are to be checked in a stone before it is used in a building?
- What do you understand by dressing of stones? Describe various methods of dressing.
- Explain the usual types of finishes used in stone masonry.
- What are the various types of Ashlar masonry? Explain any one.
- What are the factors on which a particular type of finish is selected in stone masonry work?
- Explain the differences between brick masonry and stone masonry with reference to their stability, cost and method of construction.
- State the advantages of hollow block construction over the stone masonry.
- Explain the advantages and disadvantages of concrete hollow block construction.
- What type of bonding is used in hollow concrete block construction?
- What are the precautions to be kept in view while constructing concrete block masonry.
- Explain three types of construction possible with hollow concrete blocks.
- What is reinforced brick masonry?
- Explain the special advantages of Reinforced Brick Masonry.
- Explain the reinforced brick pier with a neat sketch.
- What is reinforced brick slab? Explain with neat sketches.