What is Damp Proofing??
Damp proofing in construction is a type of moisture control applied to building walls and floors to prevent moisture from passing into the interior spaces. Damp problems are one of the most frequent problems encountered in homes. Hence, treatment to check dampness is considered to be one of the important items of work in the construction of a building. The treatment given to keep the walls, floors and basement dry is termed as damp-proofing.
- Dampness a common problem in buildings.
- It refers to access and penetration of moisture content into buildings through its walls, floors, roof, etc.
- It is important to take measures to prevent dampness.
- Such measures is called damp proofing.
- Water proofing is a treatment of the surface or structure in a building to prevent leakage.
What is the causes of Dampness??
- Moisture from ground
- Splashing of rain
- Exposed top wall
- Construction defects
Principles which is followed in damp proofing
- Mortar prepared to receive damp-proof course should be leveled.
- The horizontal damp proofing course should cover the full width of wall excluding rendering.
- If sheets or mastic asphalt are used, the gap should not less than 100mm at any point.
- At joints and corners, damp proof course should be continuous.
- Damp proofing course should not be kept exposed on the wall surface.
Methods of Damp Proofing
- Membrane damp proofing
- Integral damp proofing
- Surface treatment
- Cavity wall construction
Membrane Damp Proofing
- In this method water repellent membrane or damp proof course (DPC) between the source of dampness and part of building adjacent to it.
- DPC may be bitumen, mastic asphalt, bituminous felts, plastic sheets, cement concrete.
- DPC may be provided horizontally or vertically in floors, walls, etc.
Integral Damp Proofing
- Compounds made from chalk, talk, fullers earth, which may fill the voids of concrete under the mechanical action principle.
- Compounds like alkaline silicates, aluminium sulphate, calcium chlorides etc which reacts chemically with concrete to produce water proof concrete.
- Compounds work on water repulsion principle, like soap, petroleum, oils fatty acid compounds such as stearates of calcium, sodium, ammonia, etc. when they are mixed with concrete becomes water pepellant.
- The surface treatment consists of application of layer of water repellant substances on the surface through which moisture enters.
- The use of water repellant metallic soaps such as Calcium & Aluminium Oletes and Stearates are effective against rain water penetration.
- Surface treatment is successful when moisture is superficial.
Cavity Wall Construction
- In this method of damp preventation in which main wall of building is heilded by an outer skin wall, leaving a cavity between the two.
- This consists of depositing layer of rich cement mortar by pressure to the exposed surface of wall, pipes.
- Cement mortar is 1:3 cement sand mix.
- Mortar is shot on clean surface with cement gun under 2 to 3kg/cm2 pressure.
- Curing of mortar is done for 10 days.
What materials are used for Damping??
- Hot Bitumen
- Mastic Asphalt
- Bituminous felt
- Metal sheets
- Combination of sheets and felts
- Plastic sheets
- Cement Concrete Course
- This is highly flexible.
- Can be applied with a minimum thickness of 3mm.
- It is placed on bedding of concrete in hot condition.
- It is made by mixing bitumen & sand & mineral fillers.
- It is semi rigid material.
- It is squeezed out in hot climate or under pressure.
- It is ready made roll of dry asphalt sheets.
- It is laid on leveled flat layer of cement mortar.
- The laps is sealed with bitumen.
- It can not resist heavy load.
- It can accommodate slight movement.
- Sheets of lead, copper, aluminium is used as DPC.
- Lead sheet is more flexible.
- Thickness of sheet should be such that its weight is not kless than 20kg/m2.
- They are laid similar to bituminous felts.
- Lead will have corrosion if comes in contact with cement/lime. It is covered are embedded in cement/lime mortar.
Combination of sheets & bituminous felts
- Lead foils sandwiched between asphaltic or bituminous felts can be used as DPC.
- The combination known as Lead Core can be laid easily, is durable, efficient, economic & resistant to cracks.
- This is new type of DPC material made of black polythene sheet of 0.5mm to 1mm thickness.
- Available in 30m length in market.
- The treatment is cheaper but not permanent.
- Special bricks having water absorption not less than 4.5% of their weight can be used as DPC where dampness is excessive.
- Bricks are laid in 2 to 4 courses in cement mortar.
- The joints of bricks are kept open.
- Cement mortar 1:3 is used as bedding layer for housing other DPC.
- Small quantity of lime may be added to increases workability of mortar.
- In water used for mixing, 75gm soap is dissolved per liter of water.
- This mortar can be used for plaster of outer walls.
- Dense & sound stones, such as granite, trap, slates etc are laid in cement mortar 1:3 in two layer to form effective DPC.
- Stone should be extended to full width of wall.
- Concrete 1:2:4 mix or 1:11/2:3 mix is provided at plinth level to work as DPC.
- The thickness may vary from 4cm to 15cm.
- This layer prevent water rise in wall by capillary action.
- Where dampness is more two layer can be made.
What is the Effect of Dampness??
- Metal components of building corrodes.
- Floor finish may be damaged.
- Plaster soften and crumbles.
- Electrical fittings are damaged.
- Woodworks decays due to dry rot.
- Ugly patches on walls and ceilings.
- Materials used for wall decorations are damaged.