BRICK LAYING

Brick masonry construction is a great art since laying must be systematically done with respect to bonding, jointing and finishing. Brick laying for wall construction is done in the following steps:

1. All the bricks to be used in construction are thoroughly soaked in water so that they do not absorb the water of the mortar.

2. Mortar is spread on the top of the foundations course, over an area to be covered by the edges of the wall. The depth of spread of mortar may be about 1.5 cm.

3. The corner of the wall is constructed first. For that, one brick is laid first at the corner and pressed with hand so that the thickness of the bed-joint remains only about 1 cm. the first closer is covered with mortar on its side and then pressed against the first corner brick, such that 1 cm thick vertical joint is obtained. The excess mortar from the sides will squeeze out, which is cleaned off with trowel.

Figure. Brick laying by Conventional Method

4. The level and the alignment is checked. If the brick or closer is not in level, they are pressed gently further. Similarly, the placement of the edges of the bricks is checked so that correct offset of concrete is available.

5. Few headers and stretchers are then laid in the first course, adopting the same method as described in step 3 for the closer brick. That is, mortar is applied on the side of the brick to be laid and it is pressed against the previous brick laid earlier, so that excess mortar squeezes out from the sides. The level and alignment of these are properly checked.

6. After having laid the first course at the corner, mortar is laid and spread over the first course, to a depth of about 1.5 cm and end stretcher is laid first, by pressing it into the mortar and then hammering it slightly so that the thickness of the bed-joint is 1 cm. mortar is then applied on the side of another stretcher and pressed to the side of the corner stretcher so that thickness of the vertical joint is about 1 cm. Excess mortar which oozes out is cleaned off. This way, stretchers and headers are laid for the second course.

7. Other courses (usually four to six) are then laid at the corner. Similarly, the corner at the other end of the wall is laid. Since the corner construction at each end works as a guide for filling in-between bricks of various courses, the corner construction should be done with great care. The plumb as well as alignment should be thoroughly checked. Plumbing up by means of plumb rule should be frequently restored to as new brick work has a tendency to overhang. Vertical face is obtained by tapping the handle of the trowel against the overhanging bricks. 

8. For building the in-between portion of the wall, a cord is stretched along the top of the first course laid at each other. A brick bat is attached at either end of the cord so that it remains tout. The course is then built. The line or cord is then shifted up, corresponding to the top level of the second course, and the second course is also constructed. The procedure is repeated till the in-between wall is constructed to the height of corner masonry.

9. The corners of the wall are then raised further, and steps 7 and 8 are repeated. All the walls should be uniformly constructed so that the load on the foundations is uniform. It should be ensured that the difference in height between two adjoining walls is not more than 1m.

10. Prepends must be kept vertical. This should be checked, as the work proceeds, with the help of straight edge and the square. The straight edge is placed flat on the course and slightly projecting beyond the face. The stock of the square is then set against the underside of the straight edge with the blade coinciding with the last-formed vertical joint.

11. Bricks with one frog should be laid with its frog on its top face to ensure that they will be completely filled with mortar.

12. In the case of thick walls, mortar is first spread over the entire bed and the outer bricks are laid as described above. The inner bricks are then pressed and rubbed into position to cause some of the mortar to rise between the vertical joints, which are finally filled flush with liquid mortar so that no hollow spaces are left.

13. All loose materials, dirt and set lumps of mortar which may be lying over the surface on which the brick work is to be freshly started, should be removed with wire brush and wetted slightly.

14. After having constructed the wall, jointing and pointing is done. The procedure for jointing and pointing has been described separately. However, all the joints should be cleaned and finished after every day’s work.

QUARRYING AND BLASTING OF ROCKS

The process of taking out stones from natural rock beds is known as the quarrying. The term quarry is used to indicate the exposed surface of natural rocks. The stones, thus obtained are thus used for various engineering purposes.

Quarrying by blasting: In this method, the explosives are used to convert rocks into small pieces of stones. This method is adopted for quarrying hard stones, having no fissures or cracks. The stones obtained by blasting are usually of small size and they are used as ballast in railways, aggregates for concrete, etc.

Tools for Blasting:

Following tools are required in the process of blasting:

1. Dipper: This is shown is figure and it is used to drill a hole to the required depth.
2. Jumper: This is shown in figure and it is used to make blast holes. It is more effective in boring a nearly vertical hole.
3. Priming needle: This is shown in figure and it is used to maintain the hole when tamping is being done. It is in the form of a thin copper rod pointed at one end and provided with a loop at the other end for handling. After filling the hole with explosives, the hole is filled with tamped earth and this needle is kept at the centre so that its removal or withdrawal will develop a passage for the insertion of fuse to cause explosion. 
4. Scraping spoon: This is shown in figure and it is used to scrap or remove dust of crushed stone from blast holes. It is in the form of an iron rod with a circular plate attached to one end and provided with a loop at the other end so as to facilitate its handling.
5. Tamping bar: This is shown in figure and is used to tamp or ram the material while filling blast holes. It is in the form of a heavy brass rod of 10 mm to 15 mm in diameter and it tapers a little at the end.

Figure 1. Tools for Blasting

 Process of blasting:

1. The blast holes of required depth and diameters are made with the help of dippers and jumpers. A small quantity of water is added at intervals to make the rock soft and to convert dust into paste. Such paste is easily removed by scraping spoons.
2. The blast holes are cleaned and dried by rotating a small iron rod with a piece of dry cloth tied at its end.
3. The charge of gunpowder or dynamite is placed at the bottom of the hole. A priming needle is placed in position. It is to be coated with grease so as to make its withdrawal easy.
4. The remaining portion of the blast hole is filled in layers with dry sandy clay, moorum and ant hill earth. Each layer is to be rammed or tamped hard. The ramming is done by a tamping bar.
5. When the tamping operation is finished, the priming needle is taken out slowly by frequent turning leaving a narrow hole and it is filled with gunpowder or dynamite.
6. A fuse is inserted in the hole and it is kept projecting outside the hole to a length of about 600 mm to 900 mm. Thus a link is formed between the fuse at the top and charge of explosive at the bottom.
7. The free end of the fuse is fired and the explosion takes place and the rock is disintegrated into small blocks.

Line of least resistance: The rocks contain fissures, cracks, faults or bedding plane. When explosion occurs, gases are formed. If blast hole is tamped sufficiently hard, it will not be possible for the gases to come out through the blast hole. In such a case, the gases will follow the line of path which offers the least resistance. Such a line is known as line of least resistance or LLR. In practice, LLR is taken as the shortest distance between the centre of the blast hole and the nearest rock surface.

Precautions in blasting:

Following precautions are to be taken in the process of blasting to avoid the occurrence of serious accidents:

1. Failure of explosion: Sometimes a charge fails to explode due to any reason. In such a case, a fresh blast hole is made near the hole that has failed and the process of blasting is repeated. The fresh blast hole should not be too near the failed hole. In many cases, the explosion of fresh blast hole will also explode the charge of failed blast hole and in such a case, it may result into serious accidents.
2. Needle and tamper: These should be made of copper or bronze and not of steel. A spark is formed when steel strikes the rock. Hence, if they are of steel premature explosion will take place and it may result into serious accidents.
3. Notice of blasting: Nobody should be allowed to enter the area where blasting is being done. The notices and visible signs as red flags should be placed at suitable places along the periphery of such area. 
4. Retreat to a distance: The fuse adopted should be such that a worker can retreat to a safe distance after firing it. For larger work, the whistles or sirens may be used to warn the workers to go to a safe place before explosion takes place.
5. Seepage of water: If water is entering the blast hole, the charge of explosive should be placed in thin iron plate.
6. Skilled supervision: The work of blasting should be entertained only to the trained and experienced persons. 
7. Storing: The explosives should be stored very carefully. They should be placed in specially constructed buildings known as magazines or store houses.

CAVITY WALLS AND ITS CONSTRUCTION

A cavity wall or hollow wall is the one which consists of two separate walls, called leaves or skins, with a cavity or gap in between. The two leaves of a cavity wall may be of equal thickness if it is a non-load bearing wall, or the internal leaf may be thicker than the external leaf, to meet the structural requirements. The two portions of the wall may be connected together by metal pins or bonding bricks at suitable interval.  It also prevents the dampness to enter and acts as sound insulation. Thus they are normally the outer walls of the building. The size of cavity varies from 4 to 10 cm. The inner and outer skins should not be less than 10 cm each (half brick). 

Figure 1. Cavity wall

Advantages

Cavity walls have the following advantages over other walls:

1. There is no direct contact between the inner and outer leaves of the wall (except at the wall ties). Hence, the external moisture (dampness) cannot travel inside the building.
2. The cavity between the two leaves is full of air which is bad conductor of heat. Hence, transmission of heat from external face to the inside the room is very much reduced. Cavity walls have about 25% greater insulating value than the solid walls.
3. Cavity walls also offer good insulation against sound.
4. The nuisance of efflorescence is also very much reduced.
5. They are cheaper and economical.
6. Loads on foundations are reduced because of lesser solid thickness.

Construction

Generally, the cavity wall is set centrally over the concrete base, without any footings. According to I.S. recommendations, the lower portion of the cavity may be filled with lean concrete upto few centimeters above the existing ground level. The top of the filling should be sloped (Figure 2) with weep holes at 1 m intervals along the outer leaf of the wall. The inner leaf may be of common bricks and the outer leaf with any designed kind of facing bricks or it may also be common bricks finished with rendering. The two leaves should be tie together with wall ties.

Figure 2. Position of cavity at foundation level

Bonds for cavity wall construction should consists of stretcher bond for half brick leaves and any ordinary bond, such as English bond or Flemish bond for leaves which are one brick or more in thickness. Where solid walls are joining cavity walls, bonding of former into the latter should conform to the principle shown in figure 3. Stretchers in the solid wall should extend half brick into the inner leaf of the cavity wall and closers as shall be used for good bonding.

Figure 3. Junction between Solid Wall and Cavity Wall

Bricks should be lad very carefully to leave the cavity free from mortar droppings. Two leaves of the wall should be raised simultaneously and uniformly. The position of wall ties should be predetermined so as to have uniform spacing preferably in centres. The cavity should be made free from rubbish and mortar droppings by means of a timber batten 25 mm thick and width about 12 mm less than the cavity, resting over the ties. The battens may be lifted by means of wires or rails attached to the battens, as shown in figure 4. The batten is supported on wall ties and the brick work is carried out on either side of the batten, to the height where next row of wall ties are to be provided. After this, the batten is lifted up, cleaned of mortar droppings and replaced over the next row of wall ties.

Figure 4. Cavity Wall Construction

ACOUSTICS OF STUDIOS

A studio is a big room or a hall where sound is picked up by a microphone, and is either recorded or broadcast. It includes radio-broadcasting station, television station and sound recording studio. The basic requirements of such a studio are: (i) perfect sound proofing, and (ii) variable reverberation time, due to variable pitch and frequency of sound produced there.

The following points are noteworthy for the acoustic design of a studio.

1. The studio walls should be of rigid construction so as to completely insulate and exclude the external noise.

2. The studio should be rectangular in plan with ratio of height, breadth and length as 2:3:5. The ceiling should be flat.

3. The outer surfaces of wall should be reflective type, while the interior surfaces of walls, ceilings, floors, etc. should be of absorbent materials.

4. The noise level in the studio should be brought down to 20 to 30 dB.

5. Provision of windows should be minimum, to prevent transfer of noise from outside.

6. Air-conditioning machinery etc. should be completely isolated, and their noise should be completely insulated.

7. If there are more than one studios in a building; they should preferably be on the same floor. In no case should two studios be located one above the other; there should be a gap of atleast one floor.

8. The acoustic design of the studio should be such that echoes and near echoes are completely eliminated.

9. Heavy curtains and draperies should be used with advantage to control or regulate the time of reverberation.

10. Variable reverberation time can be obtained by providing hinged panels or shutters, with one surface of rotatable panel of absorptive material and the other of reflective material (Figure 1). Panels with hinge at the centre may also be used, having two different adsorbent materials on both the faces.

Figure 1. Hinged Panel

11. Reverberation time can also be varied by providing rotating cylinders in the ceiling of the studio. Each cylinder or drum (Figure 2) has three sectors, provided with three different absorptive materials. The cylinder can be rotated by rack and pinion arrangement, thus getting the required units of absorption for the desired reverberation time.

Figure 2. Rotable Cylinders

BUILDING BYE-LAWS

Minimum provisions designed from National Building Code (published in 1970, revised in 2005) by Town Planning Authorities, Urban Development Authorities and Municipalities, to protect the inmates living in the house, neighbours and public passing by the side of the building against structural failures, fire accidents and insanitary conditions are called BUILDING BYE-LAWS.

PURPOSE OF BUILDING BYE-LAWS

Modes of construction varies from region to region depending upon motive of owners, availability of materials, labour, construction and weather conditions. If certain rules and regulations are not made, house owner may construct residential building as per his whims and fancies. Hence, it is essential to maintain and implement the bye-laws to provide proper ventilation, privacy, security and safety between the neighbours.

OBJECTIVES OF BUILDING BYE-LAWS

•      Allows disciplined and systematic growth of buildings and towns and prevent haphazard development.

•      Protect safety of public against fire, noise, health hazards and structural failures.

•      Provide proper utilization of space. Hence, maximum efficiency in planning can be derived from these bye laws.

•      They give guidelines to the architect or an engineer in effective planning and useful in preplanning the building activates.

•      They provide health, safety and comfort to the people who live in buildings.

•      Due to these bye-laws, each building will have proper approaches, light, air and ventilation which are essential for health, safety and comfort.

MINIMUM PLOT SIZES AND BUILDING FRONTAGE

• Building frontage is the margin to be left beyond the extreme edge of the road (right of way) to the front of the building line (including excavations for foundations and projections of sunshades or balcony of superstructure).

• That is, it is the width of clearance of land to be left (before a road) within the private plot to facilitate

             • Widening of roads in future,

             • More sight distance at junctions avoiding blind corners,

             • Minimizing sound pollution for inmates of the house, and

             • To create a buffer space between public (i.e. roads) and private (plot) properties.

• Residential buildings require minimum clearance. Public buildings require more clearance. Commercial buildings as cinema halls which release a lot of rush at a time need still more clearance.

• Set back line or Front building line is the line (inside the plot) upto which we can extend our construction.

• Each plot shall have a minimum size of frontage corresponding to the type of development as given in table.

Type of residential building	Plot size (sq. m)	Frontage (m)
Detached building	Above 250	Above 12
Semi-detached building	125-250	8 to 12
Row type building	50-125	4.5 to 8

Figure 1. Building Set-back

OPEN SPACES

FRONT OPEN SPACE

Width of Street abutting the plot (m)	Front open space minimum (m)
Upto 7.5	1.5
7.5 to 18	3.0
18 to 30	4.5
Above 30	6.0

SIDE AND REAR OPEN SPACE

Height of building (m)	Side and rear open spaces (m)
10	3
15	5
18	6
21	7
24	8
27	9
30	10
40	12
45	13
50	14
55 and above	16

INTERIOR SPACE REQUIREMENT

MINIMUM SIZE OF DIFFERENT ROOMS

NO.	NAME OF ROOM	MINIMUM SIZE
1	Habitable room a)      Bed room b)      Living room c)      Drawing room d)     Dining room e)      Study room	9.5 sq. m
2	Kitchen	5 sq. m
3	a)      Bath room b)      Water closets	1.8 sq. m 1.1 sq. m
4	Store room	3 sq. m
5	Garage	12.5 sq. m
6	Staircase	15 sq. m

GENERAL FIRE SAFETY REQUIREMENTS FOR BUILDINGS

In order that fire hazards are minimized, IS: 1641-1960 recommends that the buildings shall conform to the following general requirements: 

1. All buildings and particularly buildings having more than one storey shall be provided with liberally designed and safe fireproof exits or escapes. 

Figure 1. Fire Fighting in Buildings

2. The exits shall be so placed that they are always immediately accessible and each is capable of taking all the persons on that floor as alternative escape routes may be rendered unusable and/or unsafe due to fire. 

3. Escape routes shall be well-ventilated as persons using the escapes are likely to be overcome by smoke and/or fumes which may enter from the fire. 

4. Fireproof doors shall conform rigidly to the fire safety requirements. 

5. Where fire-resisting doors are employed as cutoffs or fire breaks, they shall be maintained in good working order so that they may be readily opened to allow quick escape of persons trapped in that section of the building, and also, when necessary, prompt rescue work can be expeditiously carried out. 

6. Electrical and/or mechanical lifts, while reliable under normal conditions may not always be relied on for escape purposes in the event of a fire, as the electrical supply to the building itself may cut off or otherwise interrupted, or those relying on mechanical drive may not have the driving powder available. 

7. Lift shafts and stairways invariably serve as flues or tunnels thus increasing the fire by increased drought and their design shall be such as to reduce or avoid this possibility and consequent spread of fire. 

8. False ceiling, either for sound effects or air conditioning or other similar purposes shall be so constructed as to prevent either total or early collapse in the event of fire so that persons underneath are not fatally trapped before they have the time to reach the exits; this shall apply to cinemas, and other public or private buildings where many people congregate. 

9. Floors are required to withstand the effects of fire for the full period stated for the particular grading. The design and construction of floors shall be of such a standard that shall obviate any replacement, partial or otherwise, because experience shows that certain types of construction stand up satisfactorily against collapse and suffer when may first be considered as negligible damage, but in practice later involves complete stripping down and either total or major replacement. This consideration shall also be applied to other elements of structure where necessary. 

10. Roofs for the various fire grades of the buildings shall be designed and constructed to withstand the effect of fire for the maximum period for the particular grading, and this requires concrete or equivalent construction. 

11. Where basements are necessary for a building and where such basements are used for storage, provision shall be made for the escape of any heat arising due to fire and for liberating smoke which may be caused. 

12. The following requirements shall be provided for smoke extraction: 

(a) Unobstructed smoke extracts having direct communication with the open air shall be provided in or adjoining the external walls and in positions easily accessible for firemen in an emergency. 

(b) The area of smoke extracts shall be distributed, as far as possible, around the perimeter to encourage flow of smoke and gases where it is impracticable to provide a few large extracts, for example, not less than 3 sq. m in area, a number of small extracts having the same gross area shall be provided. 

(c) Covers to the smoke extracts shall, where practicable, be provided in the stall board and/or pavement lights at pavement level, and be constructed of light cast iron frame or other construction which may be readily broken by fire-men in emergency. The covers shall be suitably marked.