Damp Proof Course commonly known as DPC is a layer of materials applied to stop the penetration or movement of moisture inside the buildings from its walls, floors, or roof. Different methods are applied and materials are used to stop dampness in the building.
Methods of Damp Proofing Course (DPC)
The following are the methods that can be adopted for the prevention of dampness in the building:
(a) Surface Treatment
- The application of a layer of water repellent layer, substance on the surface through which moisture enters.
- Water repellent metallic soap such as calcium and aluminum and stearates are effective against rainwater penetration
- Pointing and plastering of the exposed surfaces must be done carefully using waterproofing agents like sodium or potassium silicates, aluminum or zine sulfates, barium hydroxide, and magnesium sulphate.
- The surface treatment is successful when moisture is superficial.
(b) Pressure Grouting
- In this method, the pressure is used to fill the cracks, voids in the structure of the building by cement grouting.
- Foundations of the building are subjected to grouting to make water penetration resistant.
- This method is effective to control the entry of groundwater through foundations.
- This method consists of depositing a layer of rich cement mortar by pressure to the exposed surface of walls, pipes.
- 1:3 cement sand mortar is prepared.
- Mortar is shot on a clean surface with a cement gun under 2 to 3 kg/cm2 pressure.
- The nozzle of the machine is kept at a distance of about 75 to 90 cm from the wall.
- Mortar is cured for 10 days.
(d) Integral Treatment
- It consists of adding certain components to the concrete or mortar during the process of mixing to make it impermeable by filling the pores through chemical actions or mechanical effects.
- Compounds like chalk, talc, fuller’s earth, etc. which may fill the voids under the mechanical action principle.
- Compounds like alkaline silicates, aluminium sulphates, calcium chlorides, etc. which react chemically with the concrete to produce waterproof concrete or zinc sulphates, calcium, aluminium or ammonium chlorites, iron filings, etc. act chemically.
- If 5% soap is added in the water to be used for preparing mortar the pores get closed and coating of water repellent substance stick to the wall surface which makes it sufficiently damp proof.
- Use of commercially available compounds like silica, etc.
(e) By Special Constructional Techniques
- By constructing the external wall of sufficient thickness.
- Using high-quality bricks in the construction of the external walls.
- By building the walls in rich cement mortar,
- By fixing down water pipes sufficiently so that water may not leak through the junction of the wall and roof.
- By cavity wall construction.
(f) By Providing Damp Proofing Course (DPC)
- The continuous layer of an impervious material which is provided in between the source of dampness and part of the structure is called a damp proofing course.
- In this method, a water repellent membrane or damp proof course is provided between the source of dampness and part of the building adjacent to it.
- DPC may be bitumen, mastic asphalt, bituminous felts, plastic sheet, metal sheets, cement concrete, etc.
- DPC may be provided horizontally or vertically in floors, walls, etc. as per the requirements.
Materials used for Damp Proof Course (DPC)
Following materials are used in DPC making:
a) Hot Bitumen
- This is highly flexible.
- It can be applied with a minimum thickness of 3mm.
- It is placed on a bedding of concrete in hot conditions.
b) Mastic Asphalt
- It is made by mixing bitumen, sand and mineral fillers.
- It is a semi-rigid material.
c) Bituminous Asphalt
- It is a ready-made roll of dry asphalt sheets.
- It is laid on a leveled flat layer of cement mortar.
- An overlap of 10 cm provided at the joints.
- The laps are sealed with bitumen.
- It cannot resist the heavy load.
d) Metal Sheets
- Sheets of lead, copper, aluminum are used as DPC.
- The lead sheet is more flexible.
- The thickness of the sheet should be such that its weight is not less than 20 kg/m2
- They are laid similar to bituminous felts.
- Lead sheets are completely impervious, resistant to atmospheric corrosion, can take complex shape resistant to sliding action.
- The lead will have corrosion if comes in contact with cement/lime. It is covered by bitumen.
- Copper sheets of 3mm thickness are embedded in cement/lime mortar.
- It has a high resistance to dampness, sliding, and pressure.
- Aluminum sheets are also used for DPC but not better than copper and lead.
e) Combination of Sheets and Bituminous Felts
- Lead foils sandwiched between asphaltic or bituminous felt.
- The combination known as the lead core can be laid easily, is durable, efficient, economical and resistant to cracks.
- Special bricks, having water absorption more than 4.5 % of their weight can be used as DPC where dampness is high.
- Bricks are laid in 2 to 4 courses in cement mortar.
- The joints of bricks are kept open.
- Dense and sound stones such as granite, slates, etc. are laid in cement mortar 1:3 in two layers to form effective DPC.
- The stone should be extended to the full length of the wall.
- Cement mortar 1:3 is used as a binding layer for DPC.
- A small quantity of lime may be added to increase the workability of mortar.
- 75-gram soap is dissolved per liter of water for preparing mortar, this mortar can be used for plaster of outer walls
i) Cement Concrete
- Concrete 1:2:4 or 1:1.5:3 mixture is provided at the plinth level to work as DPC.
- The thickness may vary from 4cm to 15cm.
- The layer prevents water from raise in the wall by capillary action.
- Where dampness is more two layers can be made.
j) Plastic Sheets
- This is a new type of DPC material made of a black polythene sheet of 0.5mm to 1mm thickness.
- It is available in 30m length in the market.
- The treatment is cheaper but temporary.
Reference Articles: Damp proof course
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