Building construction 1 (MASONRY)

BUILDING CONSTRUCTION

CHAPTER 01: MASONRY

BRICK MASONRY When bricks are laid in mortar in a proper systematic

manner, they form a homogeneous mass, which can withstand forces without disintegration. This mass of the structure, so made by the use of bricks is called "Brick Masonry" or simply "Brick work".

Bricks are of uniform size and shape, light in weight, durable, fire resistant, have high resale value, low maintenance cost and are easily available in plain areas.

Brick Masonry is commonly used for construction of ordinary as well as important buildings in plain areas now-a-days.

SOME IMPORTANT TERMS USED IN BRICK MASONRY

(1) BRICK An artificial structural element in the form of a

rectangular block of clay is called a “Brick ". Bricks can be manufactured of any required shape and size. The sizes of some standard bricks are given as follows:


These sizes are called "Nominal, designated or format sizes" and are used while estimating the number of bricks in a given volume of structure.

The actual sizes in which bricks are manufactured, are slightly smaller to allow for the layer of mortar present all around the brick, usually taken as 3/8 in thick.

The Actual or Work size of English standard brick, which is mostly used in Pakistan, is usually taken as 8 5/8 in 4 1/8 in x 2 5/8 in.


(2) FROG The depression provided in the face of a brick is called a "Frog".

It is provided in the brick to achieve the following purposes:

(a) To form a key of mortar in between any two adjacent courses of brick work, so as to increase the lateral strength of the structure.

(b) To reduce the weight of the bricks, so that the bricks can be laid with convenience.

(c) To provide a place for putting the impression of trade-mark or the year of manufacturing of the bricks.


(3) POSITION OF BRICKS

(a) The position of brick, when laid with its Frog upward in the horizontal plane, is termed as "Brick on bed".

(b) The position of the brick when laid on its side "9 in x 3 in", with frog in the vertical plane is called "Brick on edge".

(c) The position of brick when laid on its side "4 1/2 in x 3 in", with frog in the vertical plane is called " Brick on end".


(4) COURSEEach horizontal layer of bricks laid in mortar in a brick work is called a "course".

(5) STRETCHERBrick, laid with its length horizontal and parallel with the face of the wall or other masonry member is called a "Stretcher" and a course, in which, all the bricks are laid as Stretchers is called a “Stretching course" or "Stretcher course".


(6) HEADER

A brick laid, so that only its end shows on the face of a wall is called a "Header" and a course, in which all the bricks are laid as headers, is known as "Heading Course" or "Header course".


(7) QUOINThe external corner of the wall is called a "Quoin".

(8) QUOIN BRICKThe brick, which forms the external corner of a wall is known

as " Quoin brick".

(9) QUOIN HEADERA corner header, in the face of wall, which is a stretcher in

the side wall is known as "Quoin header".

(10) QUOIN STRETCHERA corner stretcher in the face of a wall, which is header in the

side wall is known as "Quoin stretcher".


(11) BRICK BATS The pieces of bricks, cut long their length and having

width equivalent to that of a full or half brick are called "Brick bats“.

Some common Brick Bats are shown below:


(12) QUEEN CLOSER

Queen closer is a brick, which is half as wide as full brick and is made by cutting a whole brick lengthwise into two portions.

These are generally used next to the Quoin header for creating bonds in brickwork.

(13) KING CLOSER A brick, whose one diagonal piece is cut off one corner

by a vertical plane passing through the center of one end to the center of one side.

It is actually 7/8 of a full brick but is usually called a 3/4 brick


(14) BEVELED CLOSER A brick cut longitudinally along a vertical plane, starting at the

middle of one end to the far corner. One quarter of the brick is cut off in this way.

(15) BULL NOSE BRICK A brick with rounded corners is called a “Bull Nose Brick” (16) SQUINT BRICKS These bricks are used to construct acute (>90 degree) or obtuse

(< 90 degree) corners in brick masonry. These are special forms of bricks.


(17) JAMBThe vertical sides of door or window openings provided in a wall are known as "Jambs".

(18) REVEALSThe part of the Jamb opening , which is exposed between a door or window frame and the face or back of a wall is known as " Reveal".

(19) SILLThe horizontal part (either of timber, concrete, stone, metal, etc) at the bottom of a door or window, supporting the vertical members of the frame is known as " Sill " and its height window base from the floor level is known as " Sill level ".


(20) MORTAR

The paste obtained by mixing a binding material and a fine aggregate in suitable proportions in addition to water is known as "Mortar".

Cement and Lime are used as binding materials and Sand, Surkhi, Cinder, etc. are used as fine aggregates.

The mortars are named according to the type of binding material used in their preparation such as, cement mortar, lime mortar, etc.

The mortar prepared from simple earth is known as "Mud Mortar".

The mortar not only acts as a cementing bed between any two courses of bricks but also, gives strength to the structure by holding the individual bricks together to act as a homogenous mass.

BONDSBond is the arrangement of bricks or stones in each course, so as to ensure the greatest possible interlocking and to avoid the continuity of vertical joints in two successive courses, both on the face and in the body of a wall.

OBJECTIVES OF BONDS

A bond is provided to achieve the following objectives:(a) The primary objective of providing a bond is to break the continuity of the

vertical joints in the successive courses both in the length and thickness of masonry structure. As a result, the structure will act as a bounded mass and its load will be transmitted uniformly to the foundations.

(b) To ensure longitudinal and lateral strength of the structure.

(c) To provide pleasing appearance by laying bricks symmetrically.

(d) To do masonry work quickly by engaging more masons on a job at a time.

TYPES OF BONDS(1) ENGLISH BOND

The bond, in which headers and stretchers are laid in alternate courses, is called "English bond".

TYPES OF BONDS

ENGLISH BOND

The following are the salient features of English bond:

(i) Headers and stretchers are laid in alternate courses.

(ii) In each heading course, a queen closer is placed next to quoin header and the remaining bricks are laid as headers.

(iii) Every alternate header in a course comes centrally over the joint between two stretchers in the course below, giving an approximate lap of 2 ¼ in.

TYPES OF BONDS

ENGLISH BOND

(iv) The same course will show headers or stretchers on face and back, if the thickness of the wall is an even multiple of half bricks (e.g. 9 in, 18 in, 27 in, etc.)

(v) The same course will show headers on the face and stretchers on the back and vice versa, if the thickness of the wall is an odd multiple of half brick. (13 1/2 in , 22 1/2 in , etc )

(vi) The middle portion of the thicker walls consists entirely of headers.

(vii) Every transverse joint is continuous from face to face.

TYPES OF BONDS

(2) FLEMISH BOND

The bond, in which headers and stretchers are laid alternately in the same course, is called "Flemish bond".

TYPES OF BONDS

The following are the salient features of Flemish bond:

(i) Headers and stretchers are laid alternately in the same course.

(ii) Every header in each course lies centrally over every stretcher of the underlying course.

(iii) In every alternate course a queen closer is placed next to quoin header, so as to provide a lap of approximately 2 1/4 in.

(iv) Brick bats are to be used in walls having thickness equal to an odd multiple of half brick.

Comparison of English Bond and Flemish bond

Sr No.

English Bonds Flemish bond

1 This bond consists of headers and stretchers laid in alternative courses.

This bond consists of headers and stretchers laid alternatively in each course.

2 It is strongest of all the bonds. It is less strong for walls having thickness more than 13 ½ inches.

3 It provides rough appearance especially for one brick thick walls.

It provides good appearance for all thickness of walls.

4 There are no noticeable continuous vertical joints in the structure built in this bond.

There are partly continuous vertical joints in the structure built in this bond.

5 Much attention is not required in providing this bond.

Special attention is required in providing this bond.

6 Progress of work is more. Progress of work is less.

7 It is costly because the use of brick bats is not allowed.

It is economical because brick bats are allowed for forming this bind.

TYPES OF FLEMISH BONDS

(a) DOUBLE FLEMISH BOND

The bond in which headers and stretchers are laid alternately in each course, both in the face and back of the wall, is called Double Flemish Bond.

TYPES OF FlEMISH BONDS(b) SINGLE FLEMISH BOND

The bond provided in a wall with Flemish bond in facing and English bond in backing is called "Single Flemish bond" or "Cross bond".

This bond combines the advantages of both English and Flemish bonds and simultaneously eliminates their disadvantages.

This bond is recommended where costly bricks are specified for facing in order to provide good appearance to the wall. Also, it can be made more economical by using cheap quality of bricks on the back of wall.

On the other hand, it weakens the overall strength of the wall because of maximum use of brick and existence of continuous vertical joints. Also, it can not be provided in walls having thickness less than 13 ½ in.

TYPES OF BONDS(3) HEADING BOND

The bond in which all the bricks are laid as headers in every course of a wall is called "Heading bond".

3/4 bats are laid as quoin bricks in the alternate courses to break the continuity of vertical joints, which increases the transverse strength but weakens the longitudinal strength of the wall.

This bond is commonly used for constructing steining of wells, footings of walls and columns, corbels, cornices, etc.

TYPES OF BONDS(4) STRETCHING BOND

The bond in which all the bricks are laid as stretchers in every course is called "Stretching bond”.

This bond is provided for constructing 4 ½ in thick partition walls.

TYPES OF BONDS

(5) GARDEN WALL BOND

This bond is used for constructing one brick thick garden walls, boundary walls, and other walls such as outer leaves of cavity walls to provide good appearance.

TYPES OF GARDEN WALL BONDS(a) ENGLISH GARDEN WALL BOND

The garden wall bond in which a heading course is provided after 3 or 5 stretching courses is called "English Garden Wall Bond"

TYPES OF GARDEN WALL BONDS

(b) FLEMISH GARDEN WALL BOND In this bond a header is provided after 3 or 5

stretches in each course. This bond is also known as “Sussex or Scotch

Bond".

TYPES OF BONDS

(6) RAKING BOND

The bond in which all the bricks are laid at an angle other than 900 to the facing and backing of the wall is known as "Raking bond".

This bond is used for doing inner filling of walls at suitable intervals to improve their longitudinal strength.

The angle of rake between any two adjacent courses should be 90 degree to attain maximum transverse strength of the wall.

This bond can also be used as paving in case of brick floors, 4 ½ in thick.

TYPES OF RAKING BONDS(a) HERRING BONE BOND The raking bond in which bricks are laid at an angle

of 45 degree , starting at the central line and proceeding towards the facing and backing of the wall, is called "Herring Bone Bond"

TYPES OF RAKING BONDS(b) DIAGONAL BOND

The raking bond in which bricks are laid starting from the corner in parallel rows inclined to the facing and backing of the wall is known as "Diagonal bond".

TYPES OF BONDS(7) HOOP IRON BOND

The bond in which, after every fourth or fifth course of masonry, reinforcement in the form of longitudinal ties is provided for additional strength of the wall, is called " Hoop Iron Bond".

This bond is provided for constructing 4 1/2 in thick partition walls

TYPES OF BONDS

(8) MONK BOND This bond in which two stretchers and one header

are laid alternately in each course is called "Monk bond".

This bond is used in the construction of boundary walls.

TYPES OF BONDS(9) RHOM BOND

This bond in which brick/ tiles are laid in order to have straight horizontal and vertical joints in the facing is called "Rhom bond".

This bond is used only in facing work to provide architectural beauty.

STONE MASONRY

Rock, that is removed from its natural site

and generally, cut or dressed and then

finished for building purposes, is called

"Stone" and the art of building the structure

with stones as constructional units is called

"Stone Masonry".

MAIN TYPES OF STONE MASONRY

(1) Rubble Masonry

(2) Ashlar Masonry

RUBBLE MASONRY

• The stone masonry in which either undressed or roughly dressed stones are laid is called "Rubble masonry".

• In this masonry, the joints of mortar are not of uniform thickness.

TYPES OF RUBBLE MASONRY

(a) Random Rubble masonry

(i) Uncoursed random rubble Masonry

(ii) Built to courses random rubble Masonry

(b) Squared Rubble

(i) Uncoursed squared rubble Masonry

(ii) Built to courses squared rubble Masonry

(iii) Regular coursed squared rubble Masonry

(c) Dry rubble masonry

(a) RANDOM RUBBLE MASONRY

The rubble masonry in which either undressed or

hammer dressed stones are used is called "Random

Rubble Masonry".

The strength of this masonary depends upon the bond

between the stones.

The bond should be sound both transversely and

longitudinally.

Transverse bond is obtained by the liberal use of

"Bonders" and "Throughs"

BondersBonders are stones, which reach beyond are stones, which reach beyond the middle of the wall from each face to the middle of the wall from each face to overlap in the center overlap in the center (Dog’s Teeth Bond).(Dog’s Teeth Bond).

THROUGHSTHROUGHS are stones, which extend the are stones, which extend the full thickness of the wall. full thickness of the wall.

Note:Note: Throughs should not be used in the Throughs should not be used in the external walls, as moisture may be external walls, as moisture may be conducted through them and cause conducted through them and cause dampness on the internal face.dampness on the internal face.

(i) UNCOURSED RANDOM RUBBLE MASONRY

The random rubble masonry, in which all the stones are laid without forming courses, is known as "Uncoursed Random Rubble masonry".

This masonry is the cheapest and roughest type of masonry. The stones to be used in this masonry are of different sizes and

shapes. Larger stones are used at corners and at jambs to increase their

strength. In general, stones are laid with their longer axis roughly horizontal

and along the length of the wall. The only shaping of stones that is executed is the removal of

inconvenient corners or projections with a hammer. This type of masonry is used for constructing walls of low height in

case of ordinary buildings

(ii) BUILT TO COURSES RANDOM RUBBLE MASONRY

In this type of masonry, the work is roughly leveled up to form courses, varying from 12 to 18 in thick.

In each course, headers of one course height are placed at certain intervals.

This type of masonry is used to construct residential buildings, godowns, boundary walls, etc

(b) SQUARED RUBBLE MASONRY

The Rubble masonry in which the face stones are roughly squared by hammer dressing or chisel dressing, before their actual laying is called "Squared Rubble masonry".

There are three Types of squared rubble masonry:

(i) UNCOURSED SQUARED RUBBLE MASONRY

In this type of squared rubble masonry, the stones are roughly squared and built without continuous horizontal courses .

It is used for ordinary buildings in hilly areas, where a good variety of stones are easily and cheaply available.

(ii) BUILT TO COURSES SQUARED RUBBLE MASONRY

The stones are roughly squared and laid in

courses to bond in with the larger quoin

stones.

(iii) REGULAR COURSED SQUARED RUBBLE MASONRY

This type of masonry is built in courses of varying height but the stones in any one course are of the same depth.

It is mostly used in public buildings, hospitals, schools, markets, modern residential buildings and in hilly areas, where a good quality of stone is easily and cheaply available.

(c) DRY RUBBLE MASONRY

The rubble masonry in which stones are laid without using any mortar is known as " Dry Rubble Masonry".

It is an ordinary masonry and is recommended for constructing walls of height not more than 18 ft.

In case, the height is more, three adjacent courses are laid in Squared rubble masonry, in mortar at 9 ft interval.

(2) ASHLAR MASONRY

The stone masonry in which finely dressed stones are laid in cement or lime mortar, is known as "Ashlar Masonry".

In this masonry all the joints are regular, thin, and of uniform thickness.

This type of masonry is costly in construction as involves heavy cost of dressing of stones.

This masonry is used for heavy structures, arches, architectural buildings, high piers, abutments of bridges, etc.

TYPES OF ASHLAR MASONRY

(a) ASHLER FINE / COURSED ASHLAR MASONRY

In this type of masonry stone blocks of same height are used in each course.

Every stone is fine tooled on all sides.

Thickness of Mortar joint is less than 1/16 in and is uniform through out.

(b) RANDOM COURSED ASHLAR MASONRY

This type of Ashlar masonry consists of fine

or coursed Ashlar masonry but the courses

are of varying thickness, depending upon the

character of the building.

(c) ROUGH TOOLED ASHLER MASONRY

In this type Ashler masonry, the sides of the stones are rough tooled and dressed with chisels.

Thickness of joints does not exceed ¼ in.

(d) QUARRY FACED ASHLAR MASONRY

This type of Ashlar masonry is similar to rough tooled Ashlar masonry

but there is chisel-drafted margin left rough on the face.

(e) CHAMFERED ASHLAR MASONRY

It is similar to Quarry faced except that the

edges are given a slope of 45 degree for a

depth of 1 in. or more.

(f) ASHLAR FACING

In order to reduce the cost and to give the appearance of Ashlar facing to the wall it is usual practice to construct walls with facing of Ashlar and backing of Rubble or brick masonry. Such walls are also called “Compound or Composite masonry walls”.

If the backing is of Rubble masonry, It is called “Rubble Ashlar" and if the backing is of brick work the masonry is termed as “Brick Ashlar”

COMPARISON BETWEEN BRICK MASONRY AND STONE MASONRY

(1) Stone is stronger and more durable than brick and for public buildings; it is decidedly more suitable than brick. It reflects strength in every inch of it. It is in tune with nature. Its color improves and looks more serene with age.

On the other hand, brick is an artificial product made as a copy of stone. It is flimsy material and plastering is only a camouflage for its defects.


(2) Stone is water proof. On the other hand, Brick absorbs moisture and with dampness certain salts rise in the walls from the ground and cause disintegration of bricks.

Especially brick should not be allowed to come in contact with urine or sewage and in such places it must always be covered with cement plaster or any other protective coat.


(3) Brick offers greater facility for ornamental work in plaster as a rough shape can first be given to it by means of any tool. This is not so in case of stones.

(4) Plaster does not stick so well to stones as it does to brick.

(5) On account of the regular shape and uniform size of brick, a proper bond can be obtained with comparative ease.


(6) Due to the handy size of brick, brick masonry can be more rapidly constructed than stone masonry.

(7) Brick wall requires a fixed quantity of mortar and even with careless masons, the regular shape of the brick considerably reduces the possibility of hollows being left in the body of the wall. This is not so with some stone walls.


(8) It is possible to build brick walls of any thickness e.g., 4 1/2 in, 3 in, 9 in, 13 1/2 inch etc. Whereas, the minimum thickness of ordinary stone wall is 15 in. Stone walls of a smaller thickness than 15 in, have to be constructed with properly dressed stones, which involves a comparatively high cost.

(9) Brick does not absorb as much heat as stone does. So, brick is more fire resistant than stone.

SITE SELECTION

The site of a building greatly affects its planning, design and construction.

It may be selected as required or accepted as available.

The selection of site depends upon the purpose for which the proposed building is to be constructed.

FACTORS TO BE CONSIDERED WHILE SITE SELECTION

(1) LEVEL OF THE SITEThe level of the site must be higher than that of its surroundings, so as to provide good drainage.

(2) CLIMATIC CONDITIONSThe intensity of rainfall and sub-soil water level should be low, so as to avoid dampness in the building.


(3) SUB-SOIL CONDITIONSA hard stratum should be available at a reasonable depth (3ft to 4 ft from the ground level), so as, to construct the foundations of the building safely and economically.

(4) AVAILABILITY OF MODERN AMENITIESThe site must be within municipal limits, so that, modern amenities like, water supply, electricity, sewerage, roads, etc. can be made available with more ease, if there is no provisions at present.


(5) AVAILABILITY OF OTHER FACILITIESThe site should provide an easy access from the nearest road and offer sufficient light and air. There should be good and cheap transport facilities available near the site. It is always better, if public services like, fire brigade, police station, etc, are also not very far off from the site.

(6) SURROUNDINGSThe situation and surroundings of the site must be such as to suit the purpose for which the building is to be constructed. Each type of building requires different surroundings, than for others.

GENERAL PRECAUTIONS IN SELECTION OF SITE

(1) The site consisting of reclaimed soil (made useful for cultivation) should be avoided, as far as possible.

(2) The site must not be located in water logged areas or near the bank of a river.

(3) Old quarry sites must be avoided, as far as possible.

(4) The site for a residential building should be away from the area causing foul odor or smoke nuisance due to industrial buildings.

GENERAL PRECAUTIONS IN SELECTION OF SITE

(5) The site for a residential building, school or hospital should be away from noisy areas.

(6) There should be no disabling easement.

(Easement is a right, which a person may have over another man's land by law, such as, the right to walk over it or to run a pipe through it).

ORIENTATION OF BUILDINGS

The placing of a building with respect to the geographical directions, the direction of the wind, and the path of the sun, is known as the "Orientation of buildings".

The building should be placed in such a way that it derives maximum benefit from sun, air, rain, and nature and at the same time, it is protected from their harmful effects.

The orientation also includes the arrangement of rooms of a

building, so as to provide natural comforts to the residents.

Orientation requires first priority after selection of site, for proper planning and design of a building.

FACTORS AFFECTING ORIENTATION OF BUILDINGS

(1) SURROUNDING OF THE SITE

The building is to be orientated to suit the surroundings of the site.

(2) PROXIMITY OF A ROAD OR STREET

The building should be so orientated, as to provide easy approach from the nearby road or street.


(3) THE SUN

The sun is a source of natural light and temperature.

Sunlight is a powerful agent for killing the germs of harmful diseases like, tuberculosis, typhoid, cholera, etc., which may, otherwise, breed in the dark and damp corners of a building.

It is, therefore, essential to orientate the building such that the sun rays may fall sufficiently on the building and enters the building through doors and windows. However in summer, the building should also be protected from its severe heat.


(4) WIND

The building should be so orientated that cool breeze enters the bedrooms during night in summer but not in winter.

It should also prevent direct entry of wind of heavy intensity into the building, so as to protect the residents from dust nuisance.

(5) RAIN

The building should be so orientated, so as to prevent entry of rain inside the rooms.

It should also provide minimum portion of the building subjected to direct showers of rain, so as to prevent dampness inside the building.

ORIENTATION IN DIFFERENT REGIONS

The climatic conditions, intensity of sun and direction of wind differ from region to region. It is, therefore, not possible to follow a rigid method, with regard to the orientation of buildings.

In general the Earth's surface is divided into three different regions with respect to the orientation of buildings. In these regions, the orientation is discussed separately

(1) HOT AND ARID REGION In these regions, the climate is extreme; the temperature ranges

from 50 C0 maximum to 36 C0 minimum, or, more or less.

Cloudless sky, low humidity, and high incidence of Sun's glare are the main features.

The sunny areas are hot and dry in the day time and cool to cold at night.

As far as possible, the building should be protected from day time heat and glare during summer and at the same time, the rate of heat loss at night during winter should be reduced.

In these regions the building should be oriented for the Sun, not for wind as in humid regions.

HOT AND ARID REGION (ctd)

The following points should be kept in mind while orientating building in such areas:

To minimize the heat gain during summer and take benefit for solar heat during winter, the longer walls should face north and south and shorter walls, east and west, so the least wall area is exposed to the slanting rays of Sun during fore noon and afternoon.

In other words, we can say that the longer axis of building should run east west, so as to avoid excessive heat from west side.


Provision of projections on the southern walls will give sufficient shade to the walls during summer and provision of windows and openings on the southern wall will allow sunrays to enter into rooms during winter, because the Sun's altitude is high in summers and low in winters.

Verandahs are desired on the south for protection from heat in summers and, also, for sitting out purposes in winter to enjoy the Sun's heat.


Openings in the west should be small and should be properly orientated. ( To save cost of verandah on the west, the afternoon's Sun may be kept off by providing Louvers, which are ventilators, sometimes provided in windows also, in which horizontal sloping slats allow ventilation but exclude rain and Sun's rays.)

A small tilt in the axis of the building must be given away from the west towards the south (facing near about north-west), to get maximum benefit of breeze during rainy season, autumn, and spring to ensure comfort and proper ventilation.

(2) HOT AND HUMID REGION

In this region the climate is humid, temperature in summer is moderately high and rainfall is heavy.

The prime object for orientation and design of buildings in this region is to provide free air movement through the building and to prevent the temperature rise of its inside surface above the shade temperature.

HOT AND HUMID REGION (ctd)

The following aspects should be considered while designing buildings in these areas:

The building should face the direction of the prevailing wind to obtain maximum benefit of the air movement.

A tilt, up to 45 degree may be allowed, if required, for which the loss of efficiency is only up to 20%.

Window sills should be low to ensure maximum ventilation at the normal living level.

HOT AND HUMID REGION (ctd)

Walls should be shaded from the sun, so as to prevent the temperature rise.

Protection of openings against rain is also necessary.

Building should normally have open planning, as far as possible. They should be of one room thickness, so as to ensure thorough ventilation.

(3) HILLY REGIONS

In these regions, temperature is usually much low and cold dominates according to the increasing altitude.

There is marked drop in the temperature during night.

HILLY REGIONS (ctd)The following points should be kept in mind while

orientating building in such areas:

(1) The buildings should be located in the southern slope of the hill, as they receive maximum sunshine for the greatest duration of time.

(2) The opening should be placed as to allow sunshine inside the building.

HILLY REGIONS (ctd)

(3) A massive structure with high heat capacity is useful because the heat, it stores during the day is welcome, except in very hot day.

(4) It is necessary to provide ceilings of good thermal insulation to reduce loss of heat by radiation during night.

(5) In areas, with heavy snowfall, the roof should be kept sloping to prevent accumulation of snow.

PRE-CONSTRUCTION SITE WORKS

(1) SITE SURVEY

(1) First of all site is surveyed and topographical details are drawn on the site plan. If the area is small, topographical details are drawn by metal chains but if it is large, then plane table and theodolite are used for this purpose.

(2) Contouring is done by any suitable method of contouring and the contours are drawn on the site plan.

(3) Following the contour map, site is leveled doing necessary cuttings and fillings with the help of any suitable machinery.

SITE SURVEY(4) The datum level is set out. It is a level marked on the sections of the

drawings, from which all heights and depths are marked in figures.

This level is marked by the architect. The datum is usually taken as the surface of

the finished ground floor, abbreviated on the working drawing as F.F.L.

It is set out by a leveling instrument. A peg is driven into the ground such that its

top is at the F.F.L.

SITE SURVEY

(5) The ground floor plan is marked on the ground.

First of all centre lines of all walls are marked on the ground.

Right angles are taken by cross staff, optical square or more precisely, by a Theodolite.

The lines showing the intended lines of foundation trenches are marked by driving wooden pegs along these lines.

(2) PROFILE BOARDS

These are horizontal wooden boards fixed on edge at the datum level, outside the foundation dig for a building.

The level at which these are fixed is usually basement or ground floor or a convenient no of feet, above or below it.

PROFILE BOARDS Nails or saw cuts in the top edge of these

boards show the dig lines, footing lines, walls lines and other building lines, for setting out the lower part of the building.

One profile board is set at end of each line, i.e., two for each corner, so that strings can be stretched between the nails to show any required line at any time.

Bricks are then laid in the foundation by plum bob from the extended strings.

(3) REMOVAL OF TOP SOIL

Before the foundation trenches are excavated, the surface vegetation, roots, plants, shrubs and usually all the top soil up to a depth of 150 mm to 300 mm will have to be removed, from the area of the site to be covered by the building.

This is done to ensure that the ground, upon which the structure is to be built, will be sterile (free from decomposable material i.e., organic material).

The removed top soil is valuable for subsequent use in the garden lay-out.

(4) SITE DRAINAGE The building regulations also require that sub-

soil of any site to be used for building must be effectively drained.

If the natural drainage of surface water through the ground is not sufficient, a line of agricultural drain pipes (porous pipes) can be laid on the uphill side of the site to intercept ground water that would, otherwise, flow towards building.

(5) EXCAVATION

When the setting out is completed and the profiles are in position, excavation of the trenches for the foundation is started.

The width of the trench is read off from the profiles and the depth of the trench depends upon finding a suitable sub-soil to give a firm bearing capacity (according to design).

The foundation concrete must also be below the depth at which it will not be affected by seasonal movement of the sub-soil (according to design).

It is now common practice to use earth moving machines for excavations on all contracts except on isolated small sites.

EXCAVATION

Machines, which are in most common use are Hydraulic Diggers for excavation trenches, a Tractor Shovel for reducing levels by excavation and a Dumper for transporting soil from the site.

When soil has been tipped by the Digger, it can be lifted by the Tractor Shovel and put into the Dumper, to be carried away and discharged, where ever it is required for making up levels on the site.

Soil, which is used in this way for filling must be placed in layers, well compacted and allowed to settle for many months, so that it will not subside later, if built upon.

(6) SAFETY IN EXCAVATION

Accidents in excavation are frequent and include a high proportion of causalities.

One cubic meter of soil weighs more than a ton and falling through only a short distance, even a half cubic meter of soil is sufficient to crush and kill a workman.

Great care should be taken to support the excavation, adequately

This is done by "Timbering of Trenches", which is the process of supporting the sides of trenches by means of some wooden or steel members. The timbering is extended to the full depth of the trenches. .

Timbering of Trenches

The various members used in timbering are:-

(i) POLING BOARDS The members placed vertically on the sides

of trenches directly or after providing sheeting are known as Poling boards.

The size of poling boards may vary from 1.75 cm x 32 cm. to 22.5 cm. x 4 cm.

Timbering of trenches in Hard Soil (With a central strut to each pair of Poling Boards)

Timbering of trenches in Hard Soil(With two struts to each pair of Poling Boards)

(ii) WALING, WALES OR PLANKS

The members placed horizontally on sides of the trenches or against Poling boards are known as Walings, wales or planks.

The various sizes of Walings are 10 x 7.5, 10 x 10, 15 x 15, 17.5 x 5, 22.5 x 5, 22.5 x 7.5 cm.

Their length may vary from 2.5 to 4.5 m.

(iii) STRUTS

The horizontal members of timber driven across the trenches between Poling boards or Walings are known as Struts.

The Struts are driven at a minimum distance of 2 m centre to centre.

The Struts may be circular , having diameter 7.5 m to 12.5 cm. or square 7.5 cm. to 10 x 10 cm. in section.

Timbering of trenches in Moderately Hard Soil

(With Walings strutted at alternate Poling Boards )

Timbering of trenches in Moderately Hard Soil(With a central Waling strutted at every fourth Poling Board)

Timbering of trenches in Moderately Hard Soil(With a simple Waling strutted at 2 m interval)

(iii) SHEETING

The members which are placed horizontally or vertically close to the sides of the trenches for supporting their sides are called Sheeting.

The length of sheeting may vary from 2.5 to 4.5 m.

The horizontal sheeting is supported by Poling boards and the vertical sheeting by Waling.

Timbering of trenches in Loose Soil (With horizontal sheeting)

Timbering of trenches in Loose Soil (With vertical sheeting)

(iv) RUNNERS

The members which are vertically placed behind the Walings instead of the Poling boards are called Runners.

The Runners are long planks about 7.5 cm. thick and 1.75 to 22.5 cm wide.

They are pointed at their lower end and sometimes provided with an iron shoe and iron cap.

Timbering of trenches in very

loose soil (With Runners)

DAMPNESS

The access or penetration of moisture content inside a building through its walls, floors, or roof is known as DAMPNESS.

SOURCES OF DAMPNESS Damp rising from the soil either through the bottom or

through the ground surface, adjacent to the walls.

Moisture penetrating the walls as a result of rain beating on them during continued wet weather.

Moisture penetrating into the building through defective construction, such as rain water pipes, leaking roofs, leaking or choked gutters, etc.

Damp rising from the ground either because there is no damp proof course or because the existing D.P.C. has been bridged by the earth outside, being banked up to form a flower bed or an other purpose.

ILL EFFECTS OF DAMPNESS

It causes rots to the wooden members provided in the building.

It causes corrosion of the metals, used in the construction of a building.

It causes peeling off and removal of plaster.

It causes paints to get blistered and bleached and the surface thus gets disfigured.

It causes floors of the building to remain ugly, since they cannot be cleaned well.

ILL EFFECTS OF DAMPNESS Carpets if used on the floors of a damped building, gets

destroyed earlier. All electric installations get destroyed. It reduces the life of the structure as a whole. When dampness rises into brickwork, certain salts

dissolved in it also rise with it and appear in the form of white deposit on the wall surface due to which brickwork disintegrates and falls to powder.

It causes unhygienic conditions for the occupants of the building and affects adversely their health.

Dampness produces unpleasant smell, foul air, mildew fungus, which makes it impossible to store supplies of household goods.

CAUSES OF DAMPNESS

RAIN PENETRATIONProperly constructed walls offer considerable resistance to rain penetration but its rapid penetration takes place through the joints and porous bricks or stones. Rain penetration is also possible through the roof components, cracks, and joints b/w the walls and the roof.

LEVEL OF THE SITEStructures built on a higher ground can be drained off easily and hence they are less liable to dampness. But low lying areas cannot be easily drained off and thus causes dampness in the structure.

CAUSES OF DAMPNESS

DRAINABILITY OF THE SITE

Gravel and sandy soil allow water to pass through easily whereas clayey soils retain moisture and also causes dampness due to capillary rise.

CLIMATIC CONDITIONS

Dampness is also caused due to the condensation of moisture present in the atmosphere under very cold climate. Condensation of the atmospheric moisture can be identified by the drops of moisture present on the ceilings, walls, floors etc.

CAUSES OF DAMPNESS (- ctd -) DEFECTIVE ORIENTATION

The building having its walls subjected to direct showers of rain or getting less direct sun rays, due to defective orientation is liable to dampness.

MOISTURE ENTRAPPED DURING CONSTRUCTIONWalls while being constructed are in wet conditions. These may persist moisture for a long period after the construction is over due to the use of salty or alkaline water, which causes dampness in the building.

DEFECTIVE MATERIALSDampness is also caused due to soakage of moisture by the defective materials like porous bricks, soft stones, etc. especially when they are used in external walls.

DEFECTIVE CONSTRUCTIONIn case, there is any leakage in the sewers, down water pipes, kitchens, bathrooms, etc., it will be causing dampness in the building.

PREVENTION OF DAMPNESS

PRECAUTIONS Select a sit to make sure that the first point at which water

is struck in a pit is at least 10ft below the surface of the ground even in the wet season.

Make the ground surface surrounding the building slope away from the house so that rain water drains away, before it has time to collect.

If the building is on a hill side, make sure that the land above the house is adequately drained around the building and not through it

METHODSThe following are the methods that can be adapted for the prevention of dampness in the buildings:

(1) BY SURFACE TREATMENT

The surface treatment consists in filling or blinding the pores of the material exposed to moisture by painting a water-repellent material over the surface.

Some of the materials employed are:

Sodium or potassium silicate, aluminium or zinc sulphates, barium hydroxide and magnesium sulphate in alternate applications, soft soap and alum also in alternate applications, lime and linseed oil, coal-tar, bitumen, waxes and fats, shellacs, resins and gums etc.

(2) BY INTEGRAL TREATMENT

The integral treatment consists in adding certain components to the concrete or mortar during the process of mixing, to make it more dense by filling the pores through chemical action or mechanical effect.

For example, compounds like chalk, talc, fuller’s earth etc. act mechanically and compounds like alkaline silicates, aluminium or zinc sulphates, calcium, aluminium or ammonium chlorides, iron fillings etc. act chemically.

It 5% soap is added in the water to be used for preparing the mortar, the pores get clogged and coating of water repellent substance stick to the wall surface which makes it sufficiently damp proof.

(3) BY SPECIAL CONSTRUCTIONAL TECHNIQUES

By constructing the external walls of sufficient thickness.

By using the bricks of good quality for constructing the external walls.

By building the walls in rich cement mortar.

By providing string courses and cornices.

By fixing down water pipes sufficiently so that water may not leak through the junction of walls and roof.

By constructing hollow brick walls. ( these walls are built, usually with a thick skin of 9in inside, the air space of about 2in between and the outer skin of 4 ½ in. outside. The two skins are boned together by means of galvanized iron wall ties).

(4) BY PROVIDING A DAMP PROOF COURSE

The continuous layer of an impervious material, which is provided in between the source of dampness and part of the structure is called a Damp Proof Course.

BY PROVIDING A DAMP PROOF COURSEDamp proof course is of two types:

(1) HORIZONTAL DPC

It is provided in the walls at plinth level in the form of 1 ½ in. thick layer of 1:2:4 cement concrete covered with two coat of hot bitumen or a polythene sheet or metal sheets of lead, copper or aluminum.

It is also provided in the roofs in the form of two coats of hot bitumen, bitumen felt, mastic asphalt or sheets of polythene, lead, copper, or aluminum over the R.C.C. slab.

Horizontal D.P.C. is also provided in floors if the sub-soil water table is high and moisture is likely to rise in the floors by seepage, added by the capillary action of the soil.

BY PROVIDING A DAMP PROOF COURSE

(2) VERTICAL DPC

Vertical D.P.C. is mostly provided in the external walls in the form of ¾ in. thick 1:3 cement sand plaster, coated with two washings of hot bitumen.

It is also provided to prevent the dampness into the walls of the basements from the adjacent soils.

D.P.C. IN BASEMENTS (- ctd -)

As basements are built below ground level, these are most likely to be attacked by dampness from the soil below as well as from outside the walls.

A typical basement section showing the damp proof courses is shown in fig-119.

If the head of the water below the level of the floor is high, a layer of gravel 4 ½ in. thick, is laid under the bottom of concrete of floor as shown in fig-120.

Also, gravel is filed between the walls of the basement and adjacent soil.

D.P.C. IN BASEMENTS The gravel under the floor collects the seepage water and delivers it

to the gravel outside the external walls, through the communicating pipes, buried horizontally through the concrete foundation walls.

Drain pipes or footing drains are laid around the footing buried inside the gravel.

These footing drains lead the seepage water to a natural drain, if nearby, or to a dry well.

A dry well is a pit excavated in permeable soil or one having its bottom in such soil and filled with gravel or crushed rock.

If permeable soil is not present nearby, the water is pumped out of dry wells by hand pumps or other techniques.

The EndThe End

Building construction 1 (MASONRY)

Engineering

Transcript of Building construction 1 (MASONRY)