Saturday, May 22, 2010

Waterproofing Basics

Waterproofing between Raft and PCC - membrane protection

Waterproofing in Toilets and Kitchens - liquid compound mixed with concrete (Sikka)

Waterproofing in Roof - mud fuska, bitumen coating, membrane protection ( EPDM sheet)

Waterproofing in concrete Water Tanks or Swimming pools - crystalline coatings

Waterproofing of External Walls from rain - make cavity walls, water-proof plaster

Thursday, May 20, 2010

Plastering Deductions as per IS Code 1200

For small opening up to 0.5 m2 area, no deduction in plastering is made

For opening of size 0.5m2 to 3m2 area, deduction is made on one face of the wall.

For openings of size above 3m2, deduction is made on both faces of the wall,
but the area of sill, jamb and soffits of the opening is added.

There are many other clauses in IS Code such as:
1. If both sides of wall are plastered with a different mix
2. If only one side of the wall is plastered and other side is not

For such cases, its best to follow actuals then following IS code while preparing R.A bills.

Ceramic and Vitrified Tiles

Tile can be classified as Ceramic and Vitrified.

Vitrified tiles are of much better quality then Ceramic Tiles.

Ceramic tiles are glazed only on top and if top is destroyed, then the tile would lose its color.

Vitrified tiles are uniform throughout and much more durable, less porous and scratch-proof.

Generally for the wall, ceramic tiles maybe used, but for floors vitrified tiles are prefferable.

Ceramic tiles can be manufactured locally, however vitrified tiles require high budget industrial equipment

Steel Bars in India

2 comon types of steel bars used are
  • Mild steel bars conforming to IS: 432
  • Cold-worked steel high strength deformed bars conforming to IS: 1786 (grade Fe 415 and grade Fe 500)
The numbers 415 and 500 indicate yield stresses 415 N/mm2 and 500 N/mm2 respectively

Grade Fe 415 and Fe 500 is being used most commonly nowadays because of higher yield stress and bond strength resulting in saving of steel quantity.This has limited the use of mild steel bars

Some companies have produced the thermo mechanically treated (TMT) and corrosion resistant steel (CRS) bars with added features.

Wednesday, May 19, 2010

Rebar Weight Formula

Rebar weight is defined in kg/m

Formula for measuring weight of steel bar = Square of Diameter / 164

Eg for 12mm rod

(12*12)/164 = 144/164 = .888 Kg/M

Tuesday, May 18, 2010

Article on Virtual Construction by Mr Suresh Gupta

An interesting article on Virtual Construction or BIM technology being used by a lot of Construction firms today.

Storage of Cement at Site:

Its very important to have proper storage for cement at site. The following points should be
kept in mind
  • The plinth of the store shold be about 450mm above from the NGL.
  • The cement bags should be placed on the wooden planks 200mm above the plinth.  
  • The store should be air tight.
  • The stack of cement should be coverd with Polythene.
  • FIFO system of inventory should be followed.

Monday, May 17, 2010

Some ways to judge the quality of Cement

1. Bag should have BIS mark.
2. Cement should be smooth and silky when rubbed
     between thumb and forefinger. (Fineness)
3. No lump should be visible
5. Check manufacturing date for freshness of cement
6. Packing should be done in polythene bags
7. Cement should not feel warm when hand is inserted in bag

Saturday, May 15, 2010

About Sand in Construction

  • Sand is required for making concrete, mortar and plaster.
  • Fine Sand is also referred to Jamuna sand in Delhi
  • Sieve Analysis is used for testing the Sand for Grading
  • Silt Content Test is important. Sand should have minimum silt content. This must be done at the Initial Stage itself.
  • If any Chemical impurities may possibly present, it should be tested for that also.

Some Important Terms in Contracting for Construction

Earnest Money: Is the money paid by the Contractor to the Owner at the time of submission of bid to show that the Contractor is serious about executing the works if the contract is awarded to him. For those contractors which are not successful at securing the bid, the earnest money paid by them is refunded.

Security Deposit or Performance Gaurantee: Money payable by the Contractor to the Owner in the form of a Secured Bank Gaurantee to protect the owner in the case of Contractor either abandoning the works or not executing the works as per the specifications of the contract. Performance Gaurantee may be in the range of 2 to 4 percent of the total contract value.

Retention Money: Money held back by owner(say about 5%) from the monthly bill of the Contractor to protect himself against any defects. This money is paid back at the end of defects liablity period

Defects Liability Period: is the amount of time from completion date that the contractor is liable for defective construction

Depreciation: is the decrease in value of any asset.

Depreciation has a major impact on the taxation. Depreciation is accepted as an expense in the balance sheet by the tax authorities. Depreciation increases operating expenses thereby reduces profit and income tax. However, depreciation is not an actual cash outflow from the company.

Depreciation on construction machinery helps a construction company save tax.

Liquidated Damages: is the penalty charged by the owner if the contractor does not finish the works by the approved schedule. Generally its upto 5% of the contract value.

Friday, May 14, 2010

Construction Cycle

  • Land Acquisition
  • Feasibility Study for a Particular End Use in Mind
  • Land Usage Approval for Residential, Commercial construction i.e. N.A (Non Agriculture Land) and N.O.C
  • Design - Approved by PWD office at Vikas Sadan, New Delhi
  • Environmental Clearance ( Environmental Impact Assessment Report) And Clearance by Fire Officer
  • BOQ Preparation or Costing of Project (must include overheads)
  • Tender Preparation and Inviting Tenders
  • Contract Awarding and Signing of MOU's
  • Approval of Construction Schedule
  • Construction Start and Monitoring
  • Construction Completion and Decommissioning

Types of Construction

Construction Industry can be broadly classified as:
  1. Residential Construction
  2. Commercial Construction: This includes malls, hotels, offices, etc
  3. Infrastructure Construction : This includes roads, dams. bridges, flyovers etc
  4. Industrial Construction: This includes power plants, steel mills, chemical plants, etc

Thursday, May 13, 2010

Types of Contracts

  • Fixed Fee or Lump sum Contracts (with provision for change orders)
  • Item Rate Contracts
  • Cost Plus Contracts with GMP
  • Percentage Rate Contracts with Guaranteed Maximum Price (GMP) 
  • Contract between a Govt body and a private organizations is called PPP or Public Private Partnership.
  • Supply and Erection Contracts

Components of a Centralized Air Conditioning System:

  1. Chillers

  2. AHU
  3. Ducts

  4. Water Pipes

  5. Pumps

  6. Cooling Towers

  7. Diffusers, Grills, Registers etc

  8. Mechanical Dampers, Fire Dampers, Smoke Dampers, Thermostats

Tendering Cycle Sequence

   1) Notice Inviting Tender Date

   2) Date of Bid Submission

   3) Date of Bid Opening

   4) Award of Contract

   5) Date of Notice to Proceed

   6) Date of Onsite Construction Presence

About Bricks

Indian Standards in Brickwork
  • Nominal Size of Brick (in mm) = 230 x 115 x 75
  • Nominal Size of Brick (in inches) = 9 x 4.5 x 3
  • Number of bricks per cum of brickwork = 1/(0.230 x 0.115 x 0.075) = 504 bricks
  • Number of bricks per sqm of half-brick thick wall = 1/( 0.230 x 0.075) = 58 bricks 
  • Mortar required per cum of brickwork = 0.25 cum
Brick Types:
  • Normal Bricks
  • Fly-ash Bricks 
  • Cement Hollow Blocks ( 400mm x 200mm x 200mm) (These blocks are generally hollow, else they would be very heavy to lift)

Basics of Concrete

Concrete Mix Ratios - Cement : Fine Aggregate : Coarse Aggregate
  • M10 =1:3:6
  • M15= 1:2:4
  • M20 = 1:1.5:3
  • M25 = 1:1:2
The numbering denotes strength of the concrete. The higher the number the higher the strength.
For M30 and above, only design mixes are used.

  • These mixes are based on OPC 43 cement. If OPC 53 or any other grade of cement were to be used then these ratios would change.

  • M10 means that the concrete mix should have a compressive strength of 10N/mm2 and so on

  • These ratios are based on a volumetric mix and not a mix based on weights of the ingredients

  • IS Code 456 deals with the various grades of concrete

  • RMC is Ready Mix Concrete supplied by the RMC plants to the construction site in transit mixer trucks

  • Cost of Ready-Mix-Concrete including transportation is Rs 3000 per cum

  • As the water to cement ratio increases, the strength and durability of concrete decreases. However adequate water to cement ratio must be used for workability of concrete.
Concrete is tested by:
  1. Cube Test for strength
  2. Slump Test for workability

Tuesday, May 11, 2010

Types of Cements available in India

Ordinary Portland Cement (OPC): Also referred to as grey cement or OPC, it is of much use in ordinary concrete construction. In the production of this type of cement in India, Iron (Fe2O3), Magnesium (MgO), Silica (SiO2), Alumina (AL2O3), and Sulphur trioxide (SO3) components are used.

Portland Pozolona Cement (PPC): As it prevents cracks, it is useful in the casting work of huge volumes of concrete. The rate of hydration heat is lower in this cement type. Fly ash, coal waste or burnt clay is used in the production of this category of cement. It can be availed at low cost in comparison to OPC.

Sulphate Resisting Portland Cement: This cement is beneficial in the areas where concrete has an exposure to seacoast or sea water or soil or ground water. Under any such instances, the concrete is vulnerable to sulphates attack in large amounts and can cause damage to the structure. Hence, by using this cement one can reduce the impact of damage to the structure. This cement has high demand in India.

Portland Blast Furnace slag cement (PBFSC): The rate of hydration heat is found lower in this cement type in comparison to PPC. It is most useful in massive construction projects, for example - dams

White cement: It is a kind of Ordinary Portland Cement. The content of iron oxide is maintained below 0.4% to secure whiteness. White cement is largely used to increase the aesthetic value of a construction. It is preferred for tiles and flooring works. This cement costs more than grey cement.

Important Books and Codes applicable in India for Architects and Civil Engineers

  • National Building Code 2005 - specifies minimum standard of design for buildings
  • Schedule of Rates 2007 by CPWD - Specifies the format of BOQ and Item Rate
      This book can be downloaded free of cost from the CPWD website from
      The book is listed under the 'Publications' tab on the navigation bar.
  • Analysis of Rates 2007 by CPWD - Specifies how the Item Rate has bee calculated
  • Delhi Master Plan 2021 - Species the use of land and per capita information
  • MCD Bye-Laws - Specifies construction restrictions for individual plots
  • Contracts - FIDIC and AIA (for international projects)