Definition: Purpose of Estimating - Md Aftabur...

COURSE NAME: DETAILS OF CONSTRUCTION ESTIMATING COURSE NO: CE-200

Lecture – 1

INTRODUCTION

Definition: An estimate for any construction work may be defined as the process of calculating the quantities and costs of the various items required in connection with the work. It is prepared by calculating the quantities from the dimensions of the drawings, the various items required to complete the project and multiplied with the unit cost of item concerned.

Purpose of Estimating:

To ascertain the necessary amount received by the owner to complete the proposed work and arranging fund for the same. For public work construction estimates are required to obtain administrative approval, allotment of fund and technical sanction.

To ascertain the quantity of materials required for programming timely procurement. To know the number of different categories of works that is to be employed to

complete the work within the schedule time of completion. Helps to assess the requirements of Tools, Plants and equipments required to

complete the work according to the programme. To fix up the completion period from the volume of work involved in the estimate. To justify the investment from benefit cost ratio. Estimate is required to invite tender and preparation of bills for payment. Estimate for existing property is required for valuation

Different types of estimates:

There are different types of estimates and they are as follows:

1. A detailed Estimate 2. A preliminary or rough Estimate 3. A quantity Estimate 4. Revised Estimate 5. Supplementary Estimate 6. A complete Estimate

A detailed Estimate: This includes the detailed particulars for the quantities, rates and costs of all the items involved for satisfactory completion of a project.

A preliminary Estimate: This is an approximate estimate made to find out an approximate cost in a short time thus enable the responsible authority concerned to consider the financial aspect of the scheme for according sanction to the same.

A quantity Estimate: This is a complete estimate or list of quantities for all items of work required to complete the concerned project.

Revised Estimate: Revised Estimate is a detailed estimate for the revised quantities and rates for items of works originally provided in the estimate without material deviations of a structural nature from the design originally approved for a project.

Supplementary Estimate: While a work is in progress, some changes or additional works due to material deviation of a structural nature from the design originally approved may be thought necessary for development of a project, an estimate is then prepared to include all such works. This is known as supplementary estimate.

A complete Estimate: This is an estimated cost of all items which are related to the work in addition to the “detailed estimate”.

How to prepare a detailed Estimate:

The procedure of preparation of a detailed estimate is divided into two parts,

a) Details of measurement and calculation of quantities b) Abstract of Estimated cost

Details of measurement and calculation of quantities: Include respective measurements for dimensions for all individual items involved in the whole work are taken off from the drawing of the work and entered in the respective columns of a standard measurement form as shown below. Multiplying item wise respective dimensions quantities of all items are worked out in the measurement form.

Measurement form:

Item No. Description No Length Breadth Height or Depth Quantity

Abstract of Estimated cost: is the second part in the preparation of a detailed estimate. The cost of each and every individual item of work is calculated by multiplying the quantity computed in the measurement form with the specified rate in a tabular form known as “Abstract form” and are added all together to get the actual estimated cost of work. This estimated cost of work is increased by 3-5% for any unforeseen expenditure and is called “Contingencies”. To maintain additional supervising staff at work site called “Work charged” establishment, a further amount of 2.5% is directly charged to the estimate prepared from item of work. Thus by summation of cost obtained by adding all items, contingencies and work charged establishment a detailed estimate is prepared.

Item No Description Quantity Unit Rate Amount

Factors to be considered during preparation of a detailed Estimate:

Quantity of materials Availability of materials Transportation of materials Location of sites Local Labour charges

Lump-sum item: Sometimes a lump-sum rate is provided for certain small items for which detailed quantities cannot be taken out easily or it takes sufficient time to find the detail, as front architectural or decoration work of building, site cleaning etc.

Main items of work for Building estimates:

Earthwork in excavation for foundation trenches: Earth is excavated for for foundation trenches to the exact width and depth of foundation with vertical sides and the bottom leveled both longitudinally and transversely. The quantity of earthwork is calculated by taking the dimensions of each trench length x breadth x depth.

Earthwork in filling: This consists of two parts: (a) foundation trenches and (b) plinth filling. Normally excavated earth from foundation trenches is used for filling.

(a) : For foundation filling: Quantity of earthwork = Volume of work in excavation – Volume of work in foundation.

(b) Plinth filling: Earthwork in plinth filling is calculated by taking the internal dimensions in between plinth wall and height is taken after deducting the thickness of concrete in floor.

Concrete in foundation: The concrete in foundation is taken out in cu-ft by length x breadth x thickness. The length and breadth of concrete are usually same as for excavation, only the thickness differs.

Soling: When the soil is soft or bad, one layer of dry brick or stone soling is applied below the foundation concrete. The soling layer is computed in sq-ft (length x breadth) specifying the thickness.

Damp Proof Course: This is usually a layer of cement concrete mixture in the proportion of 1:2:4 mixed with water proofing compound laid in between the plinth and superstructure walls to prevent the rise of water by capillary action from the ground. The quantity is estimated in sq-ft multiplying the length and breadth. The thickness is described in the description column.

Masonry: Masonry is computed in cu-ft(length x breadth x height). Foundation and plinth masonry is taken under one item and masonry in superstructure is taken in another item. In storied building the masonry in each story is computed separately. In taking out quantities the walls are measured as solid and then deductions are made for openings as doors, windows etc.

R.C.C work: Reinforced concrete may be for columns, beams, lintels, roof slabs etc. The quantity is worked out in cu-ft including reinforcement. The volume occupied by reinforcement is not deducted from the volume of concrete. The quantity of reinforcement is found separately.

Centering and shuttering (Form work): The cost of formwork is about 30% of cement concrete. Unless otherwise specified formwork is measured separately.

Flooring: Ground floor means floor on plinth. The floor consists of two parts, (1) bottom floor with cement concrete (1:3:6) over a flat soling (Soling is done to prevent the contamination of concrete with earth below it), (2) the top part which may be different types. The quantity is measured in sq-ft.

Plastering: Plastering usually ½” thick is calculated in sq-ft.For walls the measurements are taken for the whole face of the wall for both sides as solid and then deduction for openings are made.

ANALYSIS OF RATES

Definition: The determination of rate per unit of a particular item of work, from the cost of quantities of materials, the cost of laborers and other miscellaneous petty expenses require for its completion is known as the analysis of rate. A reasonable profit, usually 10% for the contractor is also included in the analysis of rate.

Purposes of rate analysis:

To determine the current rate per unit of an item at the locality.

To examine the viability of rates offered by contractors To calculate the quantity of materials and labour strength required for project

planning To fix up labor contract rates.

How to fix up rate per unit of an item: The following sub heads are estimated and a summation of these is the rate per unit of an item.

a) Quantity of materials and cost b) Labor costs c) Costs of equipments or tools and plant. d) Overhead e) Profit

Quantity of Course aggregate, sand and cement for different proportions: In the analysis of rate per cu-m or cft, at first a volume of 1 cu-m has been considered in calculation. But it is difficult to assess exactly the amount of each material required to produce 1 cu-m of wet concrete when deposited in place. To find out the volume of cement, sand and course aggregate assume 1 cu-m of wet concrete needs 1.54-1.57 cu-m of dry mix. In case of brick chips the value is taken as 1.57-1.6. Analysis of Rate: Example-1: Cement concrete 1:2:4 with graded stone chips for R.C.C works. Solution: Consider volume of course aggregate = 1 cu-m Total proportion = 1+2+4 = 7 Cement = 1.54* 1/7 = 0.22 cu-m Sand = 1.54* 2/7 = 0.44 cu-m or 0.22*2 = 0.44 cu-m

Stone chips = 0.22*4 = 0.88 Particulars Quantity (cu-m) Rate Amount

Materials Cement 0.22 - ……./-

Sand 0.44 - ……./- Stone chips 0.88 - ……./-

Labour Labour - - ……./- Contingencies 5% ……./- Water charges 1% ……./-

Profit ……./- Rate Per cu-m = ……./-

SPECIFICATIONS

Specification: A specification is a specific description of a particular subject. Specification specifies or describes the nature and the class of the work, materials to be used in the work, workmanship etc and is very important for the execution of the work. The cost of a work depends much on the specifications.

Necessity of specifications:

The cost of an unit quantity of work is govern by its specifications. Required to describe the quality and quantity of different materials required for a

construction work and is one of the essential contract document. A work is carried out according to its specification and the contractor is paid for the

same.

Specification includes:

a) Description of materials b) Workmanship c) Tools and plants d) Protection of new work

General specifications of a first class building:

1. Foundation and plinth: Brickwork in foundation and plinth shall be of the first class brick in cement mortar over cement concrete.

2. Filling: Foundation trenches and plinth shall be filled up with course sand. 3. D.P.C: D.P.C shall be 2.5 cm thick cement concrete .Mix ratio is 1 : 1.5: 3 4. Superstructure: Superstructure shall be of the first class brickwork in cement mortar. 5. Flooring: Mosaic flooring shall be provided in to all floors including staircase. 6. Roofing: The roof shall be 10 cm R.C.C Slab with 10 cm average lime terracing over

it. 7. Finishing: Inside and outside shall be 12mm cement plastered. The inside of drawing,

dining and bed rooms shall be distempered and rest portions white washed three coats. The outside shall be color washed over three coats of white wash.

8. Doors and windows: Doors and windows frames shall be of seasoned teak wood and shutters of 3cm thick wood paneling, Brass fitting shall be provided. Doors and windows shall be varnished with French polish.

9. Miscellaneous: Rain water pipes shall be of Asbestos cement or cast iron, finished with paint. All sanitary, water supply and electrical fittings shall be of first class materials.

COURSE NAME: DETAILS OF CONSTRUCTION ESTIMATING

COURSE NO: CE-200

Lecture – 2

DIFFERENT METHODS FOR ESTIMATING BUILDING WORKS:

The quantities of various items such as earthwork in excavation, foundation concrete, brickwork in foundation and plinth, brickwork in superstructure etc can be estimated by any of the following three methods:

1) Long and short wall method 2) Centre line method 3) Crossing method 4)

Long and short wall method: In this method the longer walls in a building are considered as long walls and measured from out -to-out and the shorter walls, in a perpendicular direction of the long walls are considered as short walls and measured from in-to-in for a particular layer of work. To calculate the length of long and short walls determine first there centre to centre lengths individually from the plan. Then the length of long wall, out-to-out may be calculated after adding half breadth of wall at each end with its centre to centre length. Thus the length of short wall measured in-to-in may be found out after subtraction half breadth at each end from its centre to centre length. Centre line method: In this method calculate the total centre line length of walls in a building and multiply the same by the breadth and depth of the respective item to get the total quantity at a time. For different sections of walls in a building, the centre line length for each type shall be worked out separately. In case of Partition wall or verandah walls joining with main wall the centre line length shall be reduced by half of the breadth of the layer of main wall that joins with the partition or verandah wall at the same level. Number of such joints are studied first to calculate the centre line length. By this method estimates may be prepared more quickly and this methods as accurate as the other methods. Crossing method: In this method calculate the overall perimeter of the building and subtract from this four times thickness of wall to obtain the centre line length. Internal walls are grouped separately to their sections and measured in between the internal faces of the main wall at that level. Principally this method is same as the centre line method but differs the process of calculations to find the centre line lengths.

DETAILED ESTIMATE OF A TWO STORIED RESIDENTIAL BUILDING:

General Specification:

1. Foundation and plinth: Brickwork in foundation and plinth shall be of first class brick in cement mortar (1:4) over cement concrete (1:3:6)

2. Filling: Foundation trenches shall be filled up with excavated earth and the plinth shall be filled up with local sand.

3. Damp-Proof-Course: DPC shall be of cement concrete (1:2:4) with water proofing compound.

4. Superstructure: Shall be of first class brickwork in cement mortar (1:6).Wall thickness are 10inch.

5. Roofing: The roof shall be of 5inch R.C.C slab with 3.5in lime terracing over it. Concrete mix ration is 1:3:6

6. Flooring: The under bed of ground floor shall be of 3inch thick CC laid over a layer of brick flat soling.

7. Plastering: Inside and outside walls shall 1/2inch thick cement mortar(1:6). Ceiling and sunshade shall be of 1/4inch cement plastered (1:4).

8. Doors and windows: 9. Painting:

Given: #. Plan of a two storied building with detailed dimension #. Detailed section of the building #. Floor to floor height = 10ft #. Door , D1 = 3.5’ x 7 , D2 = 3’ x 7’, D3 = 2.5’ x 7’ #.Window, W1 = 4’ x 4’, W2 = 3’ x 4’, W3 = 2’ x 4’ Calculation of Long and short wall: Outer long wall (2 No) = 45 ft Outer short wall (2 No) = 26ft – 10in * 2 Wall – 1 = 26ft – 10in *2 Wall – 2 = 14ft Wall – 3 (2 No) = 10ft + 6in + 1ft Wall – 4 (1 No) = 16ft + 10in + 7ft 2in + 6in + 4ft Wall – 5 (1 No) = 8 ft

No Description of item No L (ft) B (ft) H (ft) Quantity UnitSUB HEAD‐I : EARTHWORKEarthwork in excavationOuter long wall 2 45 5 5 2250.00 cftOuter short wall 2 24.34 5 5 1217.00 cftWall ‐1 1 24.34 5 5 608.50 cftWall ‐ 2 1 14 5 5 350.00 cftWall ‐ 3 2 11.5 5 5 575.00 cftWall ‐ 4 1 28.5 5 5 712.50 cftWall ‐ 5 1 8 5 5 200.00 cftTotal Earthwork = 5913.00 cftSand filling for plinthBed room 1 14 11 2.5 385.00 cftBed room 1 14 12.5 2.5 437.50 cftDrawing room 1 11 10 2.5 275.00 cftDining room 1 10 15.5 2.5 387.50 cftKitchen with passage 1 6 15.5 2.5 232.50 cftToilet with passage 1 17.83 5 2.5 222.88 cftStair case 1 16 8 2.5 320.00 cftStore room 1 7.17 8 2.5 143.40 cftToilet 1 4 8 2.5 80.00 cftTotal sand filling for plinth = 2483.78 cftEarthwork in fillingTotal Earthwork in excavation 5913.00 cftDeduct : Concrete foundation 236.52 4 1.25 1182.60 cftBrickwork in foundation (up to G.L) 236.52 2.67 3.33 2102.92 cftBrick soling 236.52 4 0.42 397.35 cftTotal Earthworkin filling = 2230.12 cft

SUB HEAD‐2 : CONCRETE WORKConcrete in foundationOuter long wall 2 45 4 1.25 450.00 cftOuter short wall 2 24.34 4 1.25 243.40 cftWall ‐1 1 24.34 4 1.25 121.70 cftWall ‐ 2 1 14 4 1.25 70.00 cftWall ‐ 3 2 11.5 4 1.25 115.00 cftWall ‐ 4 1 28.5 4 1.25 142.50 cftWall ‐ 5 1 8 4 1.25 40.00 cftTotal concrete in foundation = 1182.60 cft1" thick D.P.COuter long wall 2 45 0.83 74.70 sftOuter short wall 2 24.34 0.83 40.40 sftWall ‐1 1 24.34 0.83 20.20 sftWall ‐ 2 1 14 0.83 11.62 sftWall ‐ 3 2 11.5 0.83 19.09 sftWall ‐ 4 1 28.5 0.83 23.66 sftWall ‐ 5 1 8 0.83 6.64 sftP.W 1 8 0.5 4.00 sftP.W 1 22 0.5 11.00 sftTotal = 211.31 sftDeduction :

Notes

4

5

2

3

1

Details of Measurment and Quantities

Breadth 5' = 4' + 1' (space)Height 5' means from foundation level to Ground level (G.L)

In case of L, B ..Inner dimension are taken2.5' = 3'(betn

G.L & P.L) ‐3"(for CC)‐3"(Brick soling)17.83' = 11'+10"+6'

2.67' = ((22+42)/2)/123.33' = 10"+10"+10"+10"

DPC is usually a layer of cement concrete mixture in the proportion 1:2:4 mixed with water proofing compound laid in between the plinth and

Door, D1 3 3.5 0.83 8.72 cftD2 2 3 0.83 4.98 cftD3 2 2.5 0.83 4.15 cftCollapsible gate 1 4 0.83 3.32 cftNet total = 190.15 cft

6 Concrete in slab 46 27 0.42 521.64 cftConcrete in lintelOuter long wall 2 45 0.83 0.5 37.35 cftOuter shor wall 2 24.34 0.83 0.5 20.20 cftWall ‐1 1 24.34 0.83 0.5 10.10 cftWall ‐ 3 1 11.5 0.83 0.5 4.77 cftWall ‐ 4 1 29.5 0.83 0.5 12.24 cftP.W 1 16 0.5 0.5 4.00 cftTotal concrete in lintel = 88.67 cftConcrete in stairBase on toe wall 1 4 0.83 0.83 2.76 cftWaist slab of flight 2 9.43 4.25 0.42 33.67 cftLanding (lower& at 1st floor) 2 4 8 0.42 26.88 cftSteps 20 4 0.42 0.5 16.80 cftTotal concrete in stair = 80.10 cftConcrete in Sunshade Window,W1 4 4 1.5 0.42 10.08 cftWindow,W2 4 3 1.5 0.42 7.56 cftWindow, W3 4 2 1.5 0.42 5.04 cftTotal concrete for sunshade = 22.68 cftConcrete in flooringBed room 1 14 11 0.25 38.50 cftBed room 1 14 12.5 0.25 43.75 cftDrawing room 1 11 10 0.25 27.50 cftDining room 1 10 15.5 0.25 38.75 cftKitchen 1 6 10 0.25 15.00 cftStore room 1 7.17 8 0.25 14.34 cftToilet 1 4 5 0.25 5.00 cftToilet 1 4 8 0.25 8.00 cftPassage between toilet and din 1 13.33 5 0.25 16.66 cftTotal concrete in floor = 207.50 cft

SUB HEAD‐3 : BRICKWORKBrick flat solingMain wall 1 236.52 4 946.08 sftToe wall 1 4 2.5 10.00 sftTotal brick flat soling = 956.08 sftBrick flat soling in floorBed room 1 14 11 154.00 sftBed room 1 14 12.5 175.00 sftDrawing room 1 11 10 110.00 sftDining room 1 10 15.5 155.00 sftKitchen 1 6 10 60.00 sftStore room 1 7.17 8 57.36 sftToilet 1 4 5 20.00 sftToilet 1 4 8 32.00 sftPassage between toilet and din 1 13.33 5 66.65 sftTotal brick flat soling = 830.01 sft

9

10

12

7

8

11

superstructure walls to prevent the rise of water by capillary action from the ground.

Lintel X‐section : 10" x 6"0.5' = 6"

9.43 = sqrt (82+ 52) where,5' = 1/2 of height of one floor

0.25' = 3" (CC)Inner dimension are taken

Brick work in foundationUp to G.L1st footing 1 236.52 3.5 0.83 687.09 cft2nd footing 1 236.52 2.83 0.83 555.56 cft3rd footing 1 236.52 2.33 0.83 457.41 cft4th footing 1 236.52 1.83 0.83 359.25 cftFrom G.L to P.L 1 236.52 1.25 3 886.95 cftTotal brickwork in foundation = 2946.26 cftBrickwork in superstructureOuter long wall 2 45 0.83 10 747.00 cftOuter short wall 2 24.34 0.83 10 404.04 cftWall ‐1 1 24.34 0.83 10 202.02 cftWall ‐ 2 1 14 0.83 10 116.20 cftWall ‐ 3 2 11.5 0.83 10 190.90 cftWall ‐ 4 1 28.5 0.83 10 236.55 cftWall ‐ 5 1 8 0.83 10 66.40 cftP.W 1 8 0.5 10 40.00 cftP.W 1 22 0.5 10 110.00 cftTotal = 2113.12 cftDeduction: For Door, D1 3 3.5 0.83 7 61.01 cftD2 2 3 0.83 7 34.86 cftD3 1 2.5 0.83 7 14.53 cftFor Windwo, W1 4 4 0.83 4 53.12 cftW2 4 3 0.83 4 39.84 cftW3 4 2 0.83 4 26.56 cftFor lintel = 88.67 cftTotal deduction = 318.58 cftNet total B.W in superstructure = 1794.54 cft

SUB HEAD‐4 : PLASTERING15 1/2" thick Cement plaster to wall

Inside plastering : Bed room 1 50 10 500.00 sftBed room 1 53 10 530.00 sftDrawing room 1 42 10 420.00 sftKitchen 1 32 10 320.00 sftStore room 1 30.34 10 303.40 sftToilet 1 18 10 180.00 sftToilet 1 24 10 240.00 sftStair case 1 48 10 480.00 sftTotal = 2973.40 sftDeduction : For Door, D1 3 3.5 7 73.50 sftD2 2 3 7 42.00 sftD3 1 2.5 7 17.50 sftFor Windwo, W1 4 4 4 64.00 sftW2 4 3 4 48.00 sftW3 4 2 4 32.00 sftTotal deduction = 277.00 sftNet total inside plastering = 2696.40 sftOutside plastering 1 142 10 1420.00 sftDeduction = 277.00 sft

15(a)

15(b)

13

14

3.5' = 42"2.83' = 34"2.33' = 28"1.83' = 22"

PW = 8' (Toilet wall ‐ 6" wall)PW 22' = 11'(Drawing)+ 6'(kitchen)+ 5'(toilet)....(all are 6" wall)

50' = 2*(14+11)53' = 2*(14+12.5)50' include all inside wall of

the bed room

Net total outside plastering = 1143.00 sftTotal amout of plastering = 3839.40 sft1/4" plastering in ceilingBed room 1 14 11 154.00 sftBed room 1 14 12.5 175.00 sftDrawing room 1 11 10 110.00 sftDining room 1 10 15.5 155.00 sftKitchen 1 6 10 60.00 sftStore room 1 7.17 8 57.36 sftToilet 1 4 5 20.00 sftToilet 1 4 8 32.00 sftPassage between toilet and din 1 5 13.33 66.65 sftStair case : Under waist slab 1 4 8 32.00 sft1st landing 2 4 8 64.00 sftUnderside of 1st floor landing 1 4 8 32.00 sftTotal plastering = 958.01 sft1/4" plastering in SunshadeFor Windwo, W1 4 4 1.5 24.00 sftW2 4 3 1.5 18.00 sftW3 4 2 1.5 12.00 sftTotal plastering = 54.00 sft

15(b)

16

17

142 = 2*(45+26)

13.33' = 11' + 10" + 6' ‐ 5' (for toilet)

No Description of item Qty Unit Rate(/=) Unit Amount(/=)SUB HEAD ‐ 1: EARTHWORK

1 Earthwork in excavation 5913 cft …… cft …..2 Earthwork in filling 2230.1 cft …… cft ……3 Sand filling for plinth 2483.8 cft …… cft ……

SUB HEAD ‐ 2 : CONCRETE WORK4 Concrete in foundation (1:3:6 1182.6 cft …… cft ……5 Concrete in slab (1:3:6) 521.64 cft …… cft ……6 Concrete in lintel (1:3:6) 88.67 cft …… cft ……7 Concrete in stair (1:3:6) 80.1 cft …… cft ……8 Concrete in sunshade (1:3:6) 22.68 cft …… cft ……9 Concrete in flooring (1:3:6) 207.5 cft …… cft ……10 1" thik DPC (CC 1:2:4) 190.15 sft …… sft ……

SUB HEAD ‐ 3: BRICKWORKBrick flat soling in foundation 956.08 sftBrick soling in floor 830.01 sftBrick work in foundation 2946.3 cftBrickwork in superstructure 1794.5 cftTotal Brickwork 4740.8 cftTotal Brickwork 1786.1 sftBrick (9.5"x4.5"x2.75") 69683 noBrick (9.5"x4.5"x2.75") 6016.3 no

11 Total No of brick 75699 No …… per 1000 ……SUB HEAD ‐ 4 : PLASTERING

12 1/2" Plaster (1:6) 3840 sft …… sft ……13 1/4" Plaster (1:4) 1012 sft …… sft ……14 SUBHEAD ‐ 5 : WOOD WORK ……15 SUBHEAD ‐ 6 : STEEL & IRON WORK ……16 SUBHEAD ‐ 7 : FLOORING ……17 SUBHEAD ‐ 8 : PAINTING ……18 ……

……………………

Rate per sq ft = Grand total / plinth area

Abstract of Estimated Cost

SUBHEAD‐ 9 : W.SUPPLY & SANITATIOTotal cost = Add 5% contingency = (5% of total cost)Add 2.5% workcharge establishment = (2.5% of total cost)GRAND TOTAL = (Total cost + contingency + workcharge )Plinth Area = 45' x 26'


Lecture – 3

R.C.C WORKS Measurement of materials for cement concrete mixer: Accurate measurement of cement, fine aggregate and coarse aggregate is most necessary for producing good concrete. Cement: cement should always be measured by weight. Weight of 1bag cement = 50kg. 1 bag cement = 1.25cft Sand: sand should be measured by volume (cft or cum). Coarse aggregate: coarse aggregate may be measured by volume (cft or cum) Water: water is measured by volume. The strength and workability of concrete depend to a great extent on the amount of water used in mixing. Quality of water is measured by using water cement ratio. Water cement ratio = weight of water / weight of cement 1gallon = 4.546lit 1 lit = 0.2199gallon Controlled concrete: A concrete mix which is designed on the basis of test of the strength conducted in the laboratory on the trial mixture of cement and aggregates to be actually used in the construction is termed as controlled concrete. Reinforcing bars: The most common type of reinforcing steel is in the form of round bars often called rebar’s available in different diameters. These bars are furnished with surface deformations for the purpose of increasing resistance to slip between steel and concrete. For many years, bar sizes have been designated by no. (Say #3 bar) #3 bar means, diameter of bar = 3/8 inch.

Bar no Area (in2) Nominal weight inch mm lb/ft kg/m

2 6 0.05 0.167 0.22 3 10 0.11 0.376 0.62 4 12 0.20 0.668 0.89 5 16 0.31 1.043 1.58 6 19 0.44 1.502 2.23 7 22 0.60 2.044 3.00 8 25 0.79 2.670 3.85 9 29 1.00 3.40 4.83 10 32 1.27 4.303 6.31 11 36 1.56 5.313 7.90 14 43 2.25 7.650 11.95 18 57 4.00 13.60

Standard weight per meter in kg = D2/162 Where, D = dia in mm Concrete protection for reinforcement: To provide the steel with adequate concrete protection against fire and corrosion, the designer must maintain a certain minimum thickness of concrete cover outside of the outermost steel. The thickness required will vary depending upon the type of member and conditions of exposure. In general, the centre of main flexural bars in beams should be placed 2.5 to 3 inch from top or bottom surface of beam to furnish at least 1.5inch of clear cover for the bars and stirrups. In slabs, 1inch to the centre of the bar is sufficient to give the required 3/4inch cover. Bent up bar: The usual practice of bending of a bar near support is at an angle of 450. The angle of bend may also be 300 in shallow beams where effective depth is less than 1.5 times its breadth. Purpose of bent bars:

To resist negative moment this occurs at the regions of support. To resist shear force this is greater at the support.

When Ө = 450, Sin450 = d/x X = 1.414d For bent bar extra length required = x-a = 1.414d – d = 0.414d Total length = L + 2*0.414d When Ө = 300, Sin300 = d/x X = 1.732d For bent bar extra length required = x-a = 2d –1.732 d = 0.27d Total length = L + 2*0.27d

Detailed estimate of a R.C.C beam : Calculation of steel : 2-12mm straight , L = 10’+2”(in the wall)+6”(hook) = 10.67’ Total length = 2*10.67 = 21.34ft = 6.50m 2-19mm straight, L = 10.67’ Total length = 6.50m 2-19mm cranked, L = 10.67’+2*0.42*(15-2*2.5)” = 11.37’ Total length = 22.74ft = 6.93m For tie bar, L = 2*(10-2*1.5)+2*(15-2*1.5)+6”(hook) = 44” = 3.67’ No of tie = 10*12/6 +1 = 21 Total length = 21*3.67’ = 77.07ft = 23.50m Total 19mm bar required = (6.5+6.93)m = 13.43m = 30kg Total 12mm bar required = 6.5m = 6kg Total 10mm bar required = 23.50m = 15kg Calculation of concrete : Volume of concrete = 10*10/12*15/12 = 10.42cft

Detailed estimate of a R.C.C column : Calculation of steel : For main bar: Length of main bar,L = 10’+4’+6”(in the footing)+1’+6”(hook) = 16’ No of bar = 4 Total length = 4*16’ = 64ft = 19.51m For tie bar : No of tie =( (10’*12+4’*12)/6) +1 = 29 Length of one tie = 2*(10-1.5*2)+2*(12-2*1.5)+6”(hook) = 38” = 3.17’ Total length = 3.17*29 = 91.93ft = 28.02m For base : No of bar in one direction = (4*12-6(clear cover))/6 +1 = 8 Length of one bar = 4’-6”(cc)+6”(hook) = 4’ Total length = 4*8 = 32ft Grand total = 32*2(for both way) = 64ft = 19.51m Total 20mm bar required = 19.51m = 19.51*0.00618*(20)^2 = 49kg Total 16mm bar required = 19.51m = 19.51*0.00618*(16)^2 = 31kg Total 10mm bar required = 28.02m = 28.02*0.00618*(10)^2 = 18kg Calculation of concrete : For column = 10*10/12*12/12 + 4*12/12*14/12 = 13cft For base = 4*4*12/12 = 16cft Total concrete required = 29cft.

Detailed estimate of a R.C.C slab: Calculation of steel : Steel in long direction : 10mm @6” c/c alt ckd : No of bar = (13’*12-(10” x 2)/6) + 1 = 24 Straight bar = 12, cranked bar = 12 Length of straight bar = 20’- 4”*2(wall) + 6”(hook) = 19.83’ Additional length required for one cranked = 0.42*4.5 = 1.89” Length of one cranked bar = 19.83’+ 4*1.89” = 20.46’ Total length of straight bar = 12* 19.83’ = 238 ft = 73m Total length of cranked bar = 12*20.46’ = 246 ft = 75m Steel in short direction : 10mm@5”c/c alt ckd : No of bar = (20’*12-(10”*2)/5)+1 = 45 Straight bar = 22, cranked bar = 23 Length of straight bar = 13’-4”*2+ 6” = 12.83’ Length of one cranked bar = 12.83’+ 2*1.89 = 13.15’ Total length of straight bar = 22*12.83’ = 283 ft = 87m Total length of cranked bar = 23*13.15’ = 303 ft = 93m For extra top : Long direction : L = (10’/3 + 7.5’/3)+6” (hook) = 6.33’ Total length = 12*6.33’ = 76 ft = 23.5m Short direction : L = (13’/3)+6” = 4.83’ Total length = 2*(23*4.83) = 223 ft = 68m Grand total length of 10 mm bar = (73+75+87+93+23.5+68)m = 419.5m = 419.5*0.00618*(10)^2 = 260 kg Calculation of concrete (1:2:4) : Volume of concrete = 20*13 = 260 cft Amount of cement = 1/7*260*1.55 = 57.57 cft = 46 bag Amount of sand = 2/7*260*1.55 = 116 cft Amount of khoa = 4/7*260*1.55 = 231 cft Summary : Cement = 46 bag Sand = 116 cft Khoa = 231 cft Steel(10 mm) = 260 kg

Detailed estimate of a stair case : Calculation of steel : For 1st flight : 12mm@4”c/c , L = 3.67’+9.72’+4’+7”(into the beam)+6”(hook) = 18.47’ No of bar = (4*12/4) +1 = 13 Total length(12mm) = 13*18.47’ = 240.11ft = 73.19m In the bottom slab , 12mm bar, L= 3’+3”(hook) = 3.25’ Total length (12mm)= 13*3.25’ = 42.25ft = 12.88m In the 1st landing, L= 2.5+1.25 = 3.75’ Total (12mm)= 13*3.75 = 14.86m 12mm bar in the bottom slab , L = 3.67’+10” = 4.50’ Total length(12mm)= 13*4.50’ = 17.83m 12mm bar in the landing slab, L = 4’+2.5’+3”(hook)+7”(in the wall) = 7.33’ Total length(12mm) = 29.04m 10mm binder: No of binder = ((9.72+3.67+4+3.67+3+2.5+1.25)*12/7 )+1 = 49 Length of one bar = 4’ -6”(cc) + 6”(hook) = 4’ Total length (10mm)= 4*49 = 59.74m For Landing beam : No of straight bar = 5, L = 8’ Total length(16mm) = 5*8 = 12.19m Transverse bar : No of bar = (8*12/6)+1 = 17 L = 50” = 4.17’ Total length(10mm) = 17*4.17 = 21.59m Grand total length of 12mm bar = (73.19+12.88+14.86+17.83+29.04) = 147.8m = 132kg Grand total length of 10mm bar = 59.74+21.59 = 81.33m = 51kg Grand total length of 16mm bar = 12.19m = 20kg For 2nd flight: Same procedure Calculation of concrete : Waist slab = 2*9.72*4*6/12 = 38.88cft At bottom = 1*3.67*8*6/12= 14.68cft 1st & 2nd landing = 2*4*8*0.5 = 32cft Steps = 20*4*(1/2*0.83*0.5) = 16.6 cft Landing beam = 8*10/12*18/12 = 10cft Total amount of concrete work = 112.16cft

Detailed estimate of a pile: Calculation of steel: No Description of

item No of bar

Length Total length (ft)

L (m)

Unit weight (kg/m)

Total weight (kg)

6-16mm dia bar 6 40.5’ 243 74.06

1.58 117

10mm@8”c/c 40*12/8 = 60

3.14*(20”-3”) = 4.45’ 266.9 81.35

0.62 51

Calculation of concrete: Volume of concrete = 3.14*(20/12)^2*(1/4)*44.5 = 97cft.

Detailed Estimate of a septic tank : Calculation of various items : No Description of item No L B H Quantity Unit

1 Earth cutting : Wall 1 44.84 4 10.5 1883.28 cftTank 1 12.42 9.17 8 911.13 cftTotal Earth cutting = 2794.41 cft

2 Brickwork : Brick soling (under footing) 1 44.84 4 179.36 sftOn the floor 1 12 9.17 110.04 sftTotal Brick soling = 289.40 sftBrickwor in supersturctureLong wall 2 13.25 0.42 8 89.04 cftShort wall 1 9.17 0.42 8 30.81 cftPartition wall 1 9.17 0.42 8 30.81 cftTotal = 150.66 cftDeduction for opening 1 9.17 0.42 2 7.70 cftNet total = 142.96 cftConcrete workFooting 1 44.84 4 1 179.36 cftAt floor 1 12 9.17 0.33 36.31 cftTop slab 1 12 9.17 0.5 55.02 cftBeam 1 9.17 0.42 0.5 1.93 cftTotal = 272.62 cftPlastering : 1/2" plastering Inside wall 1 42.34 8 338.72 sftOutside wall 1 46.5 8 372.00 sftPartition wall 2 9.17 8 146.72 sftTotal = 857.44 sft1/4"plasteringAt floor 1 12 9.17 110.04 sftTop slab 1 12 9.17 110.04 sft

Calculation of steel in the wall : Short wall : For main bar : Length of main bar = 8’+2’+1’+6”(hook) = 11.5’ No of bar = (10*12/5)+1 = 25

Total length = 2*25* 11.5’ = 175.26m For two short wall = 2*175.26 = 350.52m For binder : L = 10’ No of bar = ((8+2)*12/6)+1 = 21 Total length = 2*21*10 = 128m For two wall = 2*128 = 256m Long wall : For main bar : L= 11.5’ No of bar = 33 Total length = 231.34m For two long wall = 463m For binder: L= 13.25’ No ob bar = 21 Total length = 169.62m For two wall = 340m Grand total 12mm bar required = 350.52+463 = 813.52m = 724kg Grand total 10mm bar required = 256+340 = 596m = 369kg

Detailed estimate of a retaining wall:

Calculation of steel:

No Description of item

No of bar

Length Total length (ft)

L (m)

Unit weight (kg/m)

Total weight (kg)

1

In the wall 19mm@16”c/c (30*12/

16)+1 = 24

15’+1’+1.25’+6”(hook) = 17.75’

24*17.75’ = 426’

130 2.23 289.9

19mm@16”c/c 24 9.75’ 24*9.75’ = 234’

71.32

2.23 159.04

19mm@8”c/c 48 6.75’ 324’ 98.76

2.23 220.23

16mm@7”c/c 15*12/7 = 27

30’-6”+6”= 30’ 810’ 247 1.58 390.26

16mm@5”c/c 73 17.75’ 1296’ 395 1.58 624.1 10mm@6”c/c 31 30’ 930’ 283.

46 0.62 175.75

Footing base 16mm@6”c/c 61*2 =

122 7.5’ 915’ 278.

89 1.58 440.65

10mm@8”c/c 12*2 = 24

30’ 720’ 219.45

0.62 136.06

Summary:

Total 19mm bar = 670 kg Total 16mm bar = 1456kg Total 10mm bar = 312kg

Calculation of concrete: Volume of concrete at foundation = 4*30*1.5’ = 180cft Volume of concrete at wall = (1+2)/2*15*30 = 675cft Total volume of concrete = 855cft.


Lecture – 4

FOUNDATION

Every building consists of two basic components:

Superstructure Substructure

Superstructure is usually that part of the building which is above ground and which serves the purpose of its intended use. Substructure is the lower portion of the building, usually located below ground level, which transmits the loads of the superstructure to the sub soil. Foundation: A foundation is that part of the structure which is in direct contact with the ground to which the loads are transmitted. The soil which is located immediately below the base of the foundation is called the sub soil or foundation soil. Footing: The lowermost portion of the foundation which is in direct contact with the sub soil is called footing. Functions of foundations:

• Reduction of load intensity: Foundation distributes the loads of the superstructure to a large area. So the intensity of load at its base does not exceed the safe bearing capacity of sub soil.

• Even distribution of load: Foundations distribute the non uniform load of the superstructure evenly on the sub soil such as combined footing.

• Provision of level surface: Foundation provide leveled and hard surface over which the superstructure can built.

• Lateral stability: It anchors the superstructure to the ground imparting the stability of the building against sliding & overturning due to horizontal forces.

• Safety against undermining: It provides structural safety against undermining or scouring due to flood water, borrowing etc.

• Protection against soil movement: Special foundation prevents the distress in the superstructure due to expansion or contraction of the subsoil because of moisture movement of soil.

Essential requirements of a good foundation:

• The foundation shall be constructed to sustain the dead and imposed load and to transmit

this to the sub soil in such a way that the pressure on soil do not cause excessive settlement.

• Foundation base should be rigid so that differential settlements are minimized. • Foundations should be taken sufficiently deep to guard the building against damage

caused by swelling or shrinkage of sub soil. • Foundation should be so located that its performance may not be affected due to

unexpected future influence.

Types of foundation:

Shallow foundation Deep foundation

Shallow foundation: When the foundation is placed immediately beneath the lowest part of the superstructure, it is termed as shallow foundation. A foundation is shallow if its depth is equal to or less than its width. There are various types of shallow foundations:

1. Spread footing 2. Grillage foundation 3. Eccentrically loaded footing 4. Combined footing 5. Mat or raft footing 6. Strap footing

Spread footing: Spread footings are those which spread the super imposed load of wall or column over the widen area. Spread footing may be of the following types-

(a) Wall footing: These types of footing consist of several courses of bricks. It might be two types: simple footing and stepped wall footing. In case of stepped footing, the lowest course is usually twice the breadth of wall above. The increase base width of the wall is achieved by providing 2.5in offset on either side of the wall. Depth of each course is usually 5inch. Generally a concrete base is provided at the lowest level.

(b) Column footing: Column footing is one which is provided under a column for distributing the concentrated loads in the form of uniformly distributed load on soil below. Generally column footing means reinforced cement concrete column footing. It also may different types: Single footing: Here the column load is distributed through the single spread. Stepped footing: This footing is generally used for heavily loaded column which requires greater spread. Sloped footing: In this footing the concrete base does not have uniform thickness but it is made sloped with greater thickness at its junction with the column and smaller thickness at the ends.

(c) Reinforced concrete footing: In places where the walls are subjected to relatively heavy loading and the bearing capacity of the soil on which the wall footing is to rest is very low, the wall footing results a massive structure. In such case it is desirable to provide reinforced concrete footing below the wall.

(d) Inverted arch footing: In older periods, this type of foundation used for multistoried buildings. These types of foundation greatly reduced the depth of foundation in soft soils. However with the advancement in engineering technique, inverted arch construction is rarely done these days.

Grillage foundation: When heavy structural loads from superstructure are required to be transferred to a soil of low bearing capacity, grillage foundation is often found to be lighter and more economical. This avoids deep excavation and provides necessary area at the base to reduce intensity of pressure. Depending upon material used for construction grillage foundation can be divided in two categories:

a) Steel grillage: Steel grillage foundation consists of steel beams also known as grillage beam. In this case excavations are carried to the desired depth and the bed is well leveled. This foundation bed is covered with a layer of rich mixture of concrete. This is well compacted so as to make the layer of concrete an impervious bed. Grillage beams of designed dimensions are then placed on this bed of concrete at specified distance apart using separators. The upper surface of grillage beam flanges is brought in a horizontal plane and rich cement grout is then poured all around the lower flanges of the beam. The concrete is then placed between and around the beam.

b) Timber grillage: Where the soil encountered is soft and is permanently water logged building wall can be economically supported by suitable designed grillage foundation of timber.

Eccentrically loaded footing: As far as possible, the foundation should be so shaped and proportional that the center of gravity of the imposed load is coinciding with the centre of gravity of the area of base. However when the wall or columns are to be placed closely to property lines, the required supporting areas of the base cannot be placed concentrically with the imposed load without overlapping the property line. In such case, the footing is so shaped as to have a considerable wider base with regular offsets on the inside while the outside wall face is kept flush with the boundary line. Combined footing: A spread footing which supports two or more columns is termed as combined footing. It may be following types:

(a) Rectangular (b) Trapezoidal (c) Combined between wall footing

The combined footing for column will be rectangular in shape if they carry equal loads. If the columns carry unequal loads, the footing is of trapezoidal shape. The design of combined footing should be done in such a way that C.G of column load coincides with C.G of footing area. Sometime it may require providing combined footing for column and a wall.

Mat or Raft foundation: A raft or mat is a combined footing that covers the entire area beneath a structure and supports all the walls and columns. When the allowable soil pressure is low or the building loads are heavy, the use of spread footings would cover more than one half the areas and it may prove more economical to provide mat or raft foundation. Also if the structure is liable to subsidence on account of uncertain behavior of its sub soil water condition, raft foundation should be preferred. Strap footing: If the independent footing of two columns is connected by a beam, it is then called strap footing. Strap footing may be used where distance between the columns is so great that a combined trapezoidal footing becomes quite narrow, with high bending moments. In that case each column is provided with its independent footing and a beam is used to connect the two footings. The strap beam does not remain in contact with soil and thus does not transfer any pressure to soil. Deep foundation: Deep foundation is those in which the depth of foundation is very large in comparison to its width. Situation for providing deep foundation:

The load of the super structure is heavy and its distribution is uneven. The top soil has poor bearing capacity. The subsoil water level is high so that pumping of water from the open trenches for the

shallow foundations is difficult and uneconomical. There is large fluctuation in sub soil water level. If deep strip foundation is attempted, timbering of sides is difficult to maintain or retain

the soil of the sides of trench. The structure is situated on the sea shore or river bed, where there is damage of scouring

action of water. Canal or deep drainage lines exist near the foundations. The top soil is expansive in nature.

Types of deep foundation:

1. Pile foundation 2. Pier foundation / cofferdams 3. Caissons or well foundation

Pile foundation: Pile foundation is generally used when simple spread foundation at a suitable depth is not possible either because the stratums of required bearing capacity or steep slopes are encountered. Depending upon their function or use piles may be classified in following types:

End bearing pile: End bearing piles are those which are driven into the ground until a hard stratum is reached. Such piles act as pillars’, supporting the super structure and transmitting the load down to the level at which it can safely borne by the ground. Friction piles: When piles are required to be driven at a site where the soil is weak or soft to a considerable depth, the load carried by a pile is borne by the friction developed between the side of the pile and the surrounding ground. Sheet pile: Sheet piles differ from above piles is that they are rarely used to furnish vertical support but are used to function as retaining wall. Generally used as impervious cut off to reduce seepage. Anchor piles: When piles are used to provide anchorage against horizontal pull from sheet pilling wall or other pulling forces. They are termed as anchor piles. Batter piles: When piles are driven at an inclination to resist large horizontal or inclined forces, the piles are termed as batter piles. Fender piles: When the piles are used to protect concrete deck or other water front structure from the abrasion or impact that may caused from ships are called fender piles. Compaction piles: When piles are driven in granular soil with the aim of increasing the bearing capacity of the soil, the piles are termed as compaction piles. Tension piles: The piles that are used to anchor down the structures subjected to uplift due to hydrostatic pressure or due to overturning moment. Pier foundation: When a heavy loaded building is to be situated in sandy soil or soft soil, overlaying hard bed at responsible depth, pier foundation is used to transfer the load to the hard bed below. These methods consist of sinking vertical shafts up to hard bed and filling them with concrete. Cofferdams: A cofferdam may be defined as a temporary structure constructed in a river or lake or any other water bearing surface for excluding water from given site in order to perform various operation on dry surface. Types: Earthen cofferdam: It essentially consists of an earthen embankment built around the area to be enclosed. Rock fill cofferdam: If the depth of water to be retained by the embankment of cofferdam is of order of 1.8 to 3m, stone or rubble is used for the embankment. This is known as rock fill cofferdam. Single walled cofferdam: This type of cofferdam is used in places where the area to be enclosed is very small and the depth of water is more about 4.5to 6m. Doubled walled cofferdam: For cofferdam required to enclose large area, in deep water single wall type becomes uneconomical as larger sections would be necessary to resist water pressure. Double walled cofferdam is provided in such situations. Crib cofferdam: In deep water where it is difficult to penetrate the guide piles or sheet piles into the hard bed bellow, crib cofferdam is used. In this type, the sheet piles are supported by a series of wooden cribs. A crib is a frame work of horizontal timbers installed in alternate courses to form pockets which can be filled with earth or stones.

Cellular cofferdam: This type of cofferdam is mostly used for de watering large areas in places where the depth of water may be of the order of 18 to 21m. These are mostly used during the construction of marine structures like dams. Cellular cofferdam is made by driving straight web steel, sheet plates arranged to form a series of inter connected cells. The cells are constructed in various shapes. Finally the cells are filled with clay sand or gravel to make them suitable against various forces to which they are likely to be subjected to two common shapes of the cellular cofferdam are : Circular type and diaphragm type. Caissons: A caisson may be defined as a watertight structure made up of wood, steel or reinforced concrete for foundations of bridge, piers, abutments in rivers and lakes dock structure for shore protection. The caisson remains in its position and ultimately becomes an integral part of the permanent structure. Types of caissons:

1. Open caisson 2. Box caisson 3. Pneumatic caisson

Open caisson: Depending upon their shapes, open caissons can be further classified as: Single wall open caisson: This is a box type structure having no top or bottom (during construction and mainly consists of vertical walls) Cylindrical open caisson (well): This may be defined as a cylindrical shell made up of timber, masonry, steel or reinforced concrete with a cutting edge which is sunk by excavating the soil with in the shell. To facilitate sinking of the caisson, water jets are sometimes used around the sides which decrease the skin friction. This caisson is also known as well caisson. Open caisson with dredging wells: This type of caisson has the distinction of being employed for the deepest foundation for bridge piers, abutments and other similar structure. The caisson in this case is rectangular or square in plan and is further subdivided into smaller section from inside forming open walls. The outside walls as well as the inside divider walls are normally made up of reinforced concrete. Box caisson: This type of caisson is similar to open caisson except that it is closed at the bottom. This caisson is cast and cured on the land and when required it is launched in water. The caisson is sunk by filling sand, gravel or concrete in the empty space inside. The function of the sand layer is to uniformly distribute the superimposed loads over the soil below the caisson and thus avoid tilting of caisson. Pneumatic caisson: This type of caisson is closed at top and open (during construction) at the bottom. The water is excluded from the caisson chamber by means of compressed air. Machine foundation:

Another type of foundation is used for machine. Design of this foundation involves careful study of the vibration characteristics of the foundation system. All parts of machine foundation should be designed for maximum stresses due to worst combination of vertical loads, torque, longitudinal and transverse forces, stresses due to temperature variation and foundation dead load. The foundation block should have the designed thickness and should be reinforced both at top and bottom even if reinforcements are not required from design consideration. Causes of failure of foundation: The causes of failure of foundations may be summarized under the following heads:

1. Unequal settlement of the subsoil. 2. Unequal settlement of masonry. 3. Horizontal movement of the soil adjoining the structure. 4. Shrinkage due to withdrawal of moisture from the soil below the foundation. 5. Lateral pressure tending to overturn the structure. 6. Action of atmosphere. 7. Lateral escape of the soil below the foundation.


Lecture – 5

BRICK MASONRY

Definition: The construction carried out using bricks and mortar is known as brick masonry. Types of brick:

1. Traditional bricks 2. Modular bricks

Strength of brick masonry depends on:

Quality of bricks Quality of mortar Method of bonding used

Unbounded wall, even constructed with good quality bricks and mortar has little strength and stability. Causes of preferring brick masonry over other types of masonry:

1) The bricks are of uniform size and shape. So they can be laid in any define pattern. 2) The art of brick laying can be under stood very easily and even unskilled masons can

do the brick masonry. Stone masonry construction requires highly skilled masons. 3) Bricks do not need any dressing like stone. 4) Bricks are very light in weight and convenient in size. They can be easily handled. 5) As the bricks are light in weight, they do not require any lifting apparatus. 6) They can be manufactured at all sites and there is no problem of its availability. Also

they do not require transportation from long distance. 7) Light partition wall and ornamental works can be easily constructed by brick

masonry. Traditional bricks: The bricks that are generally used in construction are known as traditional bricks. General size of the brick is 9.5” x 4.5” x 2.75”. Modular bricks: Any bricks which are of same uniform size of PWD standard are known as modular bricks. Moulded bricks: Moulded bricks are those which are manufactured in special shapes and sizes to be used for giving architechtural shapes. Such bricks are used for cornices, slopping walls etc. Stretcher: A stretcher is the longer face of the brick. A course of brick in which all the bricks are laid is known as stretcher course if all the stretchers are on facing (9.5 x 2.75)

Header: A header is the shorter face of the brick. A course of brick in which all the bricks are laid as headers on the facing is known as header course or heading courses (4.5 x 2.75) Lap: Lap is the horizontal distance between the vertical joints of successive brick courses. Lap should not be less than 1/4th of the length of the brick. Perpend: A perpend is an imaginary vertical line which includes the vertical joint separating two adjoining bricks. Quoin: It is a corner or external angle on the face side of a wall. Racking back: It is the termination of a wall in a stepped fashion. Toothing: It is the termination of the wall in such a fashion that each alternate course at the end projects in order to provide adequate bond if the wall is continued horizontally at a latter stage. Bed: Bed is the lower surface of the brick when laid flat. (9.5 x 4.5) Closer: It is a portion of brick with the cut made longitudinally and is used to close up bond at the end of the course. A closer helps in preventing the joints of successive courses to come in a vertical line. Closer may be of various types:

a) Queen closer: It is a portion of a brick obtained by cutting a brick lengthwise into two portions. Thus a queen closer is a brick which is half as wide as the full brick. This is known as queen closer. When the queen closer is broken into two pieces, it is known as queen closer quarter.

b) King closer: It is obtained by cutting a corner of the brick joining middle points of width and length of the brick. It is used near door and window openings to get good arrangement of the mortar joints.

c) Beveled closer: It is obtained by cutting a triangular portion of the brick, half width and full length.

d) Mitred closer: Mitred closer is obtained by cutting a triangular part of the brick from one of its header face. Cutting face is inclined at 45 to 60 degree with longer stretcher face of the brick.

e) Bat: It is a piece of brick. If bat is half brick in length, it is known as half bat, it it is 3/4th of the brick it is known as three quarter bat. Bat may be beveled also which is then called beveled bat.

f) Bullnose: The brick moulded with round angle is known as bullnose. Bonds in brick work:

Bond is an arrangement of bricks in a course by which formation of continuous vertical joints both in the face and body of the wall can be prevented and the individual units are tied together. Types of bond:

1. Stretcher bond 2. Header bond 3. English bond 4. Flemish bond 5. Facing bond 6. English cross bond 7. Brick on edge bond 8. Dutch bond 9. Raking bond 10. Zigzag bond 11. Garden wall bond

Stretcher bond: Stretcher bond or stretching bond is one in which all the bricks are laid as stretchers on the faces of walls. This pattern is used only for those walls which have thickness half brick i.e. 4.5 inch. Header bond: Header bond or heading bond is the one in which all the bricks are laid as headers on the faces of walls. This pattern is used only when the thickness of the wall is equal to one brick i.e. 9.5 inch. This is achieved by using three quarter brick bats. English bond: This is most commonly used bond for all wall thickness. This bond is considered to be the strongest. The bond consists of alternate courses of headers and stretchers. In order to break vertical joints in successive joints it is essential to place queen closer after first header in each heading course. Flemish bond: In this type of bond, each course is comprised of alternate headers and stretchers. Every alternate course starts with a header at corner then queen closer are placed. It has two types:

a) Double Flemish bond: In the double Flemish bond, each course presents the same appearance both in the front face as well as in the back face. Alternate headers and stretchers are laid in each course.

b) Single Flemish bond: Single Flemish bond is comprised of double Flemish bond facing and English bond backing and hearting in each course.

Facing bond: In this bond, a header course is laid after several stretcher courses. The bond may be used to lay costly facing bricks on exposed face and low quality bricks in the backing of the walls. English cross bond: This is modification of English bond used to improve the appearance of the wall. Special features are: → Alternate course of header and stretcher → A header is introduced next to the quoin stretcher in every alternate stretcher course.

Brick on edge bond: In this type bond stretcher brick courses are used on edges instead of bed. This bond is weak in strength but is economical. Dutch bond: This is another modification form of English bond. In this bond the courses are strengthen: → Alternate layer of headers and stretchers are provided. → Every stretcher course started with a three quarter bat. → In every stretcher courses, a header is placed next to the bat. Raking bond: It is the bond in which filling of thick walls is done by laying bricks in inclined direction with the facing of walls. It is of two types:

a) Diagonal bond: In this type of bond filling bricks are inclined in one direction only. Here the bricks are arranged at 45degree in such a way that extreme corners of the series remain in contact with the extreme line of stretchers.

b) Herring bone bond: This bond is very useful for walls having thickness more than 4bricks. Bricks are laid at an angle 45 degree from the centre line of the wall in plan.

Zig zag bond: This bond is similar to herring bone bond except that the bricks are laid in zig zag fashion. It is most commonly used for making ornamental panels in brick flooring. Garden wall bond: This type of bond is used for garden wall, boundary walls where thickness of wall is one brick thick and it does not exceed two meters. It has three types:

a) Garden wall English bond: In this bond, header course is provided only after three to five stretchers courses. In each header course a queen closer is placed next to quoin header. In stretcher courses, quoin headers are placed in alternate courses.

b) Garden wall Flemish bond: In this bond each courses contain one header after three to five stretcher continuously placed. Each alternate layer contain 3/4th brick bats placed next to quoin header. Then another header is placed.

c) Garden wall monk bond: This is special type of garden wall Flemish bond in which each course contain one header after two successive stretchers. Every alternate course contain a quoin header followed by 3/4th brick bat.


Lecture – 6

SCAFFOLDING

Scaffolding is a temporary frame work of timber or steel work i.e. elements having platforms at different levels to enable masons to work at different height of building. The scaffolding should be stable and should be strong enough to support workmen and other construction material placed on the platform of scaffolding. Part of scaffolding:

1. Standards: These are the vertical member of the frame work, supported on the ground or embedded into the ground.

2. Ledgers: These are horizontal members running parallel to the walls. 3. Braces: These are diagonal members running or fixed on standard to provide stiffness

to scaffolding. 4. Put logs: These are transverse members, placed at right angle to the wall one end

supported on ledgers and other end on the wall. 5. Transoms: These are those put logs whose both ends are supported on ledgers. 6. Bridle: This is a member used to bridge a wall opening, supports one end of put log at

the opening. 7. Boarding: These are horizontal platform to support workmen and material. These are

supported on the put log. 8. Guard rail: This is a rail provided like a ledger at the working level. 9. Toe board: These are boards, placed parallel to ledgers, supported on put log to give

protection at the level of working plat form. Types of scaffolding:

1. Brick layers scaffolding or single scaffolding 2. Masons scaffolding or double scaffolding 3. Steel scaffolding 4. Needle or cantilever scaffolding 5. Trestle scaffolding 6. Suspended scaffolding 7. Gantries 8. Patented scaffolding

Brick layer scaffolding: This consists of a single frame work of standards, ledgers, and putlogs etc, constructed parallel to the wall at a distance of about 1.2m. the standards are place at 2 to 2.5m interval. Ledgers connect the standards and are provided at a vertical interval of 1.2 to 1.5m. Putlogs are placed with one end of the ledgers and other end in the hole left in the wall at an interval of 1.2 to 1.5m. Such scaffolding is commonly used for brick lying and is also called put log scaffolding. Double scaffolding:

In stone masonry, it is very difficult to provide holes in the wall to support putlogs. In that case, scaffolding consists of two rows is used. Each row forms a separate vertical formwork. First row is placed at 20 to 30 cm away from the wall. While the other form work is placed 1m distance from first one. Put logs are then supported on both the frames. Cross braces are provided to make scaffolding more strong and durable. Steel scaffolding: Steel scaffolding is similar to the masons scaffolding except that the steel tubes are used in place of wooden members. Standards are spaced about 3m apart and connected with the help of steel tube ledgers at a vertical interval of about 1.8m. Advantage of steel scaffolding:

They can be used for very large height. They can more strong and durable. They can be easily assembled. They are fire resistant. They have high scrap value.

Disadvantage of steel scaffolding: They have high initial cost. They require skilled labour. They required periodical painting.

Needle or cantilever scaffolding: Cantilever scaffolding is used under the following circumstances:

Hard firm ground is not available. When construction is to be carried on the side of a very busy road where construction

of single and double scaffolding is not possible. When construction is to be carried out at a very large height of a multi storied

building. The scaffolding may be single type or double type. In the former type, the standards are supported on series of needles taken out through openings or through holes in the wall. In the second type the needle and projecting beams are strutted the floor through the openings. Trestle scaffolding: In this type of scaffolding, working platform are supported on ladders, tripod etc. they do not need any standards, putlogs etc. They can be easily shifted from one place to another place. It is mostly used for minor repairs or painting works in side the rooms. Suspended scaffolding: This type of scaffolding is mostly used for maintenance works such as painting, pointing, distempering, white washing etc. in this arrangement working platform is suspended from the roofs or parapet walls by means of ropes, chains or wires. Rope or chain ends are kept anchord on the terrace and working platform is suspended from other ends of the ropes. Gantries: Gantries are used when very heavy stone blocks are required to be lifted to put them in position of their use. It is two types:

a) Gantry with a crane b) Platform gantry

Patented scaffolding: These days various patented types of scaffolding useful for certain specific purposes. In all these scaffoldings, the working platform is supported on brackets which can be adjusted to any height. Points to be kept in view in scaffolding:

Standards to be made to rest on hard and firm ground. If such a surface is not available standards may be made to rest on common timber sole plates.

Scaffolding should not be loaded heavily. The scaffold should be tied to the building at suitable levels. Scaffolds can be tied to

buildings by providing horizontal and vertical bullies inside the building and securing scaffolds to it by tying put logs through window or door.

Working platforms should be raised by lengthening standards and providing additional ledgers and put logs.

Holes left in the wall, after put logs have been withdrawn should be filled with masonry work immediately.

Standards should be spaced according to the load they have to carry and also according to the section of the standards.

For structures like domes, towers, chimneys etc. special patented scaffolding should be used.


Lecture – 7

PAINTING, DISTEMPERING AND WHITE WASHING

Paints are liquid compositions of pigments and binders which when applied to the surface in thin coats dry to form a solid film to impart the surface a decorative finish and giving protection from weathering, corrosion and other chemical and biological attacks. Characteristics of an ideal paint:

1. It should form hard and durable surface. 2. It should give attractive appearance. 3. It should be cheap and readily available. 4. It should be such that it can be applied easily to the surfaces. 5. It should have good spreading property. 6. It should dry in reasonable period. 7. It should not show hair cracks on drying. 8. It should form film of uniform color on drying. 9. It should be stable for longer period. 10. It should not be affected by atmospheric agencies.

Constituents of paint: Paint generally made up of following constituents:

1. Base: A base is a solid substance in a form of fine powder, forming the bulk of paint. A base in paint provides of opaque coating to hide the surface to be painted.

2. Vehicle: These are liquid substances which hold the different ingredients of paint in liquid suspension. The vehicle makes it possible to spread the paint evenly on the surface.

3. Drier: Driers are used to accelerate the process of drying and hardening by extracting oxygen from the atmospheric and transferring it to the vehicle.

4. Colouring pigments: Colouring pigments are added to the base to have different desired colours.

5. Solvent or thickness: Solvents are added to the paint to make it thin so that it can be easily applied on surfaces. It also helps the paint in penetrating through the porous surface of the background.

Classification and types of paint: Classification based on binders:

a) Oil paints b) Paints based on non oil resins c) Cellulose paints d) Water based paints e) Miscellaneous paints

Classification based on ultimate use: a) General purpose paints including prime coat and finishing coat paints.

b) Acid and alkali resistant paints. c) Fire resistant paints. d) Fungicidal paints. e) Miscellaneous paints such as fire resistant paint, anti condensation paint etc.

Mixed classification: a) Aluminum paints b) Anti corrosive paints c) Asbestos paints d) Bituminous paint e) Bronze paints f) Casein paints g) Cellulose paints h) Colloidal paints i) Cement based paints j) Emulsion paints k) Enamel paints l) Graphite paints m) Oil paints n) Plastic paints o) Silicate paints p) Synthetic rubber paint

Painting on different surfaces: Painting on new wood work: The painting on new wood work is done in the following steps: Preparation of surface: For good results wood work should be well seasoned and should not contain more than 15% moisture. Dust is totally removed from the surface. Knotting: Knotting is the process of covering or killing all knots in the wood work with a substance through which the resin cannot come out. Priming: After knotting, the surface is lightly rubbed smooth with a abrasive paper. Priming consists of applying first coat of paint to fill all the pores. Stopping: It is the process of rubbing down the wood surface by means of glass paper after prime coat is applied and then filling up all cracks, all nail holes, open joints with putty. After putty dries up, the surface is rubbed again with glass paper. Under coating: After stopping second and successive coatings are applied. This is known as under coating. This coat serves as foundation to the finish coat. Finishing coat: Finishing coat is applied after the under coat is perfectly dry. This coat is applied very carefully so that finished surface is smooth, uniform and free from patches. Repainting old wood work: Before repairing old wood work, the old paint having cracks and blisters should be removed by applying 1kg of caustic soda in 5litres of water. Then the old paints get dissolved. After removing the old paint, the surface is properly cleaned and rubbed with glass paper. The cleaned surface is then given two or three coats of paint. Painting new iron and steel work: Iron and steel surface are painted so that rusting is prevented. The process is:

The surface is cleaned of scale and rust by scrapping or brushing with wire steel brush. Oil grease etc are removed by washing the surface with petrol, benzene or lime water.

The cleaned surface is treated with a film of phosphoric acid. It protects the surface from rusting.

The prime or first coat is then applied. After the prime coat has dried, two or more under coats are applied with a brush or

spray gun. Each successive coat must be applied after previous coat is dried completely.

After that the final coat of the desired type of paint is applied. Repainting old iron and steel work: Before repainting, the old surface is thoroughly cleaned by soap water. The grease may be cleaned by washing the surface with lime and water. However if the old paint has cracked, it has to be removed by flame cleaning. The surface is then scrapped with wire brush and washed with solution of caustic soda and fresh slaked lime. After the surface is prepared, painting is carried out as for new surface. Painting plastered surface: Newly plastered surface may contain considerable moisture. Hence painting should be restore to after 3to 6 months of plastering. Calcareous surface like lime or cement plastered surfaces are highly alkaline because lime is liberated during hydration of cement. Due to this, oil based paints and distempers are liable to alkali resistant primer. Absorption of liquid from paint is known as suction. High suction may make the paint difficult to apply and leave the coating in an under bound condition. If the surfaces show high suction, it should be treated with suitable primer. Defects in painting:

1. Blistering: it is the defect caused due to the formation of bubbles under the film of paint. This defect occurs by water vapor trapped behind painted surface.

2. Bloom: in this defect, dull patches are formed on finished surface. It occurs due to bad ventilation.

3. Sagging: this defect occurs due to application of too thick paint. 4. Fading: this is the gradual loss of color of paint due to the effect of sunlight on

pigment. 5. Flaking: it is the dislocation of some portion of painted surface, resulting from poor

adhesion. 6. Flashing: it is the formation of glossy patches on the painted surface resulting from

bad workmanship, cheap paint or weather action. 7. Grinning: this defect is caused when the final coat does not have sufficient opacity so

that background is clearly seen. 8. Running: this defect occurs when the surface to be painted is too smooth. Due to this,

the paint runs back and leaves small area uncovered. 9. Sponification: this is the formation of soap patches on the painted surface due to

chemical action of alkalis. Distempering: Distempers are considered as water paints. Distemper is composed of a base such as whiting or chalk, a carrier as water, a binder as glue and coloring agent i.e. coloring pigments.

Process of distempering: Preparation of surface: The surface to be distempered should be thoroughly rubbed and cleaned. The efflorescence patches should be carefully wiped out by clean cloth. The irregularities in surface should be filled with putty. If distempering is to be done on new surface it should be kept exposed for 3to 6months so that all the moisture evaporates. If it is to be done on old surface, old loose distemper should be removed by scrapping. New cement plaster surface should be washed with solution of zinc sulphate in water and allowed to dry. Prime coat: After cleaning the prepared surface, priming coat should be applied. For readymade distempers, prime coat as suggested by the manufacturer. Coats of distempers: Distempers are applied in 2to3 coats. However next coat should be applied only when the previous coat has dried up and become hard. Distempering should be done in dry weather to achieve best results. White washing and color washing: White washing and color washing of surfaces of buildings is necessary on both hygienic and aesthetic reasons. Preparation of white wash: white wash is prepared from fat lime. The lime is slaked at the site and mixed and stirred with about five litres of water for one kg of unslaked lime to make a thin cream. This should be allowed to stand for a period of 24 hours and then should be screened through a clean coarse cloth. Then one kg of gum is dissolved in each cum of lime cream. About 1.3kg of sodium chloride dissolved in water also added for every 10kg of lime. Small quantity of ultra marine blue may be added to the last two coats of white wash solution. Preparation of surface: The new surface should be thoroughly cleaned off all dirt, dust and mortar drop before white wash is to be applied. Old surfaces already white washed should be broomed to remove all dirt and dust. All loose scales of lime wash and other foreign matter should be removed. Where heavy scalling has taken place, the entire surface should be scrapped clean. Application of white wash: White wash is applied with brush to the specified number of coats (generally three). The operation in each coat should consist of a stroke of the brush from the top down wards, another from bottom upwards over first stroke. Another coat horizontally from the right to left and from left to right before it dries. Each coat should allowed to dry before the next coat is applied. The white washing on ceiling should be done prior to that on wall. Color washing: Color washing is prepared by adding coloring pigment to white wash. Generally used pigments are yellow earth, red ocher and blue vitriol. These are crushed to powder before mixing. The color wash is applied in the same fashion as white wash. For color washing on new surface, the first primary coat should be of white wash and the subsequent coats should be of color wash.


Lecture – 8

PLASTERING

Plastering is the process of covering rough surfaces of walls, columns, ceilings and other building components with thin coat of plastic mortars to form a smooth durable surface. The coating of plastic material is termed as plaster. Plastering on external exposed surface is known as rendering. Objects of plastering:

To protect the external surfaces against penetration of rain, water and other atmospheric agencies.

To give smooth surface in which dust dirt can’t lodge. To give decorative effect. To protect surface against vermin. To conceal interior materials or defective workmanship.

Requirements of good plaster:

It should adhere to the background and should remain adhered during all variations in seasons and other atmospheric conditions.

It should be hard and durable. It should possess good workability. It should be possible to apply it during all weather conditions. It should be cheap. It should effectively check penetration of moisture.

Types of mortars for plastering: Selection of type of mortar for plastering depends upon the following factors:

1. Availability of binding materials. 2. Durability requirements. 3. Finishing requirements. 4. Atmospheric conditions and variations in weather. 5. Location of surface.

Following types of mortars are commonly used for plastering: i. Lime mortar

ii. Cement mortar iii. Lime cement mortar

Tools for plastering:

Gauging trowel: Gauging trowel is used for taking mortar from the mortar pan, dashing it against the wall and then spreading and pressing it. The end of this trowel blade may be either pointed or bull nosed. Float: Float is used for applying and spreading mortar on the surface. It is made of either metal or wood. Metal float made of thin tempered steel is known as laying trowel. The laying trowel is used for laying the plaster material and for trowel ling so as to get desired finish. The wooden float commonly known as skimming float is used for the finishing coat of plaster. Floating rule: It is used for checking the level of plastered surface between successive screeds. Miscellaneous tools: These include plumb bob, sprit level, set square, straight edges, brushes etc. Method of plastering: Preparation of surface for plastering: The surface of the background should be prepared as follows –

All the projections extending more than 13mm from the general face of the masonry should be knocked off so as to maintain thinner plaster layer.

All the joints in the masonry should be raked for a depth of about 20mm.Raked joints should be properly cleaned from all loose dust and mortar.

Oily, greasy and efflorescence spots should be removed either by brushing, scrapping or both.

If the wall to be plastered is very old, the surface of wall should be made rough by scrapping it with some tool.

After carrying out all the above mentioned processes, the prepared surface should be thoroughly washed with water and wet before plastering is started.

In order to maintain uniform thickness of plaster, the screeds are formed on the prepared wall before plastering. Patches of plaster 150mmx150mm are first of all applied at an interval of about 2m both horizontally and vertically. The two dots lying in a vertical plan are plumbed by means of plumb bob. After fixing dots, vertical strips of mortar are formed between dots. These strips are known as screeds. These are used for maintaining even thickness of plaster.

Lime plaster: Lime plaster is applied either in three coats or in two coats. Before applying plaster, the background is prepared as desired above: Three coat plaster: In a three coat plaster, the first coat is known as rendering coat, second coat is known as floating coat and third coat is known as setting coat or finishing coat. Application of rendering coat: The mortar is forcibly applied with masons trowel and pressed well into joints and over the surface. The thickness should be such as to cover all inequalities of the surface. This is allowed to slightly harden and then scratched criss cross with the trowel. The surface is left to set at least for 7 days. Application of floating coat: The rendering coat is cleaned off from all dirt, dust and other loose mortar droppings. It is lightly wetted. Patches 15cmx15cm are applied at suitable

spacing to act as gauges. The mortar is then thrown with masons trowel spread and rubbed to the required plain surface with wooden float. Application of finishing: In case of lime sand mortar the finishing coat is applied immediately after the floating coat. Finishing coat consists of cream of lime (4:1), applied with steel trowel and rubbed and finished smooth. The rubbing is continued till it is quite dry. It is left for 1day and then curing is done for at least 7days. In lime surki mortar finishing coat is applied 7days after the floating coat is applied, after cleaning the surface. The finishing coat is rubbed hard and finished smooth. Two coat plaster: In this case the rendering coat is a combination of the rendering, floating coats of three coat plaster and is done under one continuous operation. The finishing is then applied in a manner similar to the three coat plaster. Cement plaster and cement lime plaster: Cement plaster is applied either in two coats or in three coats, the former being more common. For interior work, single coat plaster is sometime provided. Two coat plaster:

The background is prepared by racking the joint to a depth of 20mm, cleaning the surface and well watering it.

If the surface to be plastered is very uneven, a preliminary coat is applied to fill up the hollows, before the first coat.

The first coat or rendering coat of plaster is then applied. The cement mortar is applied on the surface between the successive screeds to maintain exact thickness and the surface is properly finished.

Before the rendering coat is hardened, it is suitably worked to provide mechanical key for the final or finishing coat. The rendering coat is kept wet at least 2 days and then allowed to dry completely.

Before applying final or finishing coat, the rendering coat is damped evenly. The final coat is applied with wooden floats to a true even surface and finished with steel trowels. This coat should be started from top towards bottom and completed in one operation to eliminate joints.

Three coat plaster: The process for applying three coat plaster is similar to the two coat plaster except that an intermediate coat known as floating coat is applied. The purpose of this coat is to bring the plaster to an even surface. The rendering coat is rough. Floating coat is applied 4to 7days after first coat. Finishing coat is applied about 6hours after the application of floating coat. Single coat plaster: This is used only in inferior quality work. It is applied similar to two coat plasters except the rendering coat. It is finished of immediately after it is sufficiently hardened. Types of plaster finishes:

1) Smooth cast finish: In this finish work, smooth, leveled surface is obtained. The mortar for the finish may be made of cement and fine sand in the ratio of 1:3. Mortar is applied with the help of wooden float.

2) Sand faced finish: This is obtained by plastering in two coats. First coat is applied in 1:4 cement sand mortar for 12mm thickness. It is provided with zig zag lines. After curing for 7days, the second coat is applied in the thickness of 8mm. mortar for second coat is prepared from cement sand ratio 1:1. The surface of final coat is finished by rubbing clean and fine sand by means of wooden float.

3) Rough cast finish: In this, the mortar for final coat contains fine sand as well as coarse aggregate in ratio 1:1.5:3. The mortar is dashed against prepared plastered surface by means of large trowel. The surface is then roughly finished by wooden float. Such finish is water proof, durable and resistant to cracking.

4) Dry dash: In this , the final coat having cement sand mix proportion of 1:3. Clean pebbles are the dashed against the surface, so that they are held in position. The pebbles may be lightly pressed into the mortar with wooden float.

5) Depeter finish: This is similar to pebble dash finish in which pieces of gravel are pressed with hand on the surface. Gravels or flint of different colours may be used to obtain beautiful patterns.

6) Scrapped finish: In this the final coat is applied to about 6to 12mm and after few hours, when it has stiffened, the surface is scrapped in patterns for a depth of 3mm.for scrapping steel straight edges are used. Such surface is less liable to cracks.

7) Textured finish: This is used with stucco plastering. Ornamental patterns or textured surfaces are made on the final coat of stucco plastering.

Special material used for plastering: Acoustic plaster: This contains gypsum mixtures applied as final coat in finishing the plastered surface. Such a coat undergoes chemical reaction resulting in production of gas bubbles and consequent formation of tiny openings in the coat. These honey combed minute openings absorb sound. This is used for the interiors wall of halls, auditorium etc. Asbestos marble plaster: This is made of cement, asbestos and finely crushed marble imparting Mable like finish. Barium plaster: It is made from cement, sand and barium sulphate. It is provided in X-ray rooms to protect the person working in it. Granite silicon plaster: This is used for superior type of construction because it has quick setting and highly elastic properties. Gypsum plaster (plaster of Paris): It is obtained from heating finely ground gypsum heated at 160 to 1700 C. It hardens within 3to 4 minutes of adding water. To extend the setting time, suitable retarders are used. It is generally used in combination with lime for ornamental work and for repairing holes and cracks. Kenee’s cement plaser: Keenes cement is obtained by calcinating plaster of paris with alum. This is very hard and sets in few days taking white, glass like polish. It is used for ornamental and decorative plastering. Martin’s cement plaster: Martin’s cement is obtained when pearl ash is calcined with plaster of paris. It has quick setting properties and forms a white hard surface on drying. Parian cement plaster: It is obtained when barax is calcined with plaster of paris. It is used for interior work. Scagliola plaster: It is obtained by dissolving keenes cement and colouring pigments in glue. It appears like marble.

Sirapite plaster: It is obtained when plaster of paris is slaked in petroleum. It has quick setting and fire resisting properties. It produces white hard surface on drying. Snowcrete and colourcrete cements: These are trade names given to white and coloured cement respectively. These are used on external wall to create good appearance. Thistle hardwall: It is a product of high grade gypsum. It sets rapidly and produces excellent finish. It is used for interior work. Defects in plastering:

• Blistering of plastered surface: This is the formation of small patches of plaster swelling out beyond the plastered surface.

• Cracking: Cracking consists of formation of cracks in plaster work resulting due to : → imperfect preparation of background. → discontinuity of surface. → movement of plaster surface due to expansion or shrinkage. → excessive shrinkage due to application of thick coat. →faulty workmanship.

• Falling of plaster: Following may be the reason of this defect: → bond of plaster with background may not perfect. → too much thermal changes. → imperfect bond between successive coats of plaster.

• Crazing: It is the formation of a series of hair cracks on plastered surface due to the same reasons that cause cracking.

• Efflorescene: It is the whitish crystalline substance which appears on the surface due to presence of salts in plaster making materials as well as building materials like bricks, sand and cement etc. It effects the adhesion of paint to the wall surface.

• Flaking: It is the formation of very loose mass of plastered surface due to poor bond between successive coats.

• Peeling: It is the complete dislocation of some portion of plastered surface resulting in the formation of a patch.

• Popping: It is the formation of conical hole in the plastered surface due to presence of some particles that expand during setting.

• Rust stains: These are sometimes formed when plaster is applied on metals. • Uneven surface: This is obtained purely due to poor workmanship.

Remedies of plaster defects: Following measures if employed will result in minimization of defect:

1. The surface to be plastered should be properly prepared. 2. The finished surface of the plaster should not be trowel led excessively. 3. Superior quality of bricks should be used for brick works. 4. Water used in construction should be free from soluble salts. 5. Efflorescence if any should be removed by rubbing the surface with brushes.

Alternatively a solution of one part of HCL or H2SO4 with 4 or 5 parts of clean water may be applied on the affected surface with brushes.

6. Water should not be used for washing the surface to remove efflorescence. 7. Surfaces should be painted only when efflorescence has fully ceased. 8. Proper damp proof course should be laid correctly.


Lecture – 9

POINTING

The term pointing is applied to the finishing of mortar joints in masonry. In exposed masonry, joints are considered to be weakest and most vulnerable spots from which rain water or dampness can enter. Pointing consists of raking the joints to a depth of 10 to 20 mm and filling it with better quality of mortar in desired shape. Pointing is completed with the following mortar mixes:

a. Lime mortar: 1:2 mix b. Cement mortar: 1:3 mix

Preparation of surface: New work: All the joints are raked down to a depth of 20mm while the mortar in the joint is still soft. The surface of the joints are then cleaned and thoroughly wetted. Old work: All loose pointing and superfluous mortar on the surface and in the joints are removed. The joints and surface are cleaned and then thoroughly wetted. Method of pointing: After preparing the surface, mortar is carefully placed in desired shape in these joints. A small trowel is used for placing the mortar in the joint, the mortar is pressed to bring perfect contact between the old interior mortar of the joint and new mortar. The pointed surface is kept wet for at least a week or till it sets after application. Types of pointing:

1. Flush pointing 2. Recessed pointing 3. Rubbed, keyed or grooved pointing 4. Beaded pointing 5. Struck pointing 6. Tuck pointing 7. V pointing 8. Weathered pointing

Flush pointing: This type of pointing is formed by pressing mortar in the raked joint and by finishing off flush with the edges of masonry units. The edges are neatly trimmed with trowel and straight edge. Recessed pointing: The pointing is done by pressing the mortar back from the edges by 5mm of more. The face of the pointing is kept vertical by a suitable tool. Rubbed, keyed or grooved pointing: This is a modification of flush pointing by forming a groove at its mid height, by a pointing tool.

Beaded pointing: This is special type of pointing formed by steel or ironed with a concave edge. It gives good appearance, but is liable to damage easily. Struck pointing: This is a modification of flush pointing in which the face of the pointing is kept inclined, with its upper edge pressed inside the face by 10mm. This pointing drains water easily. Tuck pointing: It is formed by first pressing the mortar in the raked joint and finishing flush with the face while the pressed mortar is green. Groove having 5mm width and 3mm depth is cut in the centre of the groove. This groove is then filled in or tucked in with white cement putty, kept projecting beyond the face of the joint by 3mm. V pointing: This type of pointing is formed by making a groove of V shaped with the help of steel rod. Weathered pointing: This type of pointing is made by making a projection in the form of V shape.

Definition: Purpose of Estimating - Md Aftabur...

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