A damp proof course is a layer in the walls of your property that help prevent moisture from move up the walls and into the living area. This is commonly referred to as rising damp.
To understand the importance of a DPC and what it does, we need to understand just what rising damp is and how it causes problems. In a property with no DPC or retrofit works, water will rise up through capillary action, up through the wall and over time, make plaster pop and crumble, create damp spots on internal walls, and eventually lead to mould and worse.
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. It can be define as a material that resists the passage of water with no hydro-static pressure and waterproof as a treatment that resists the passage of water under pressure. Generally, damp proofing keeps moisture out of a building where vapor barriers keep interior moisture from getting into walls.
Also check: Causes of dampness in building
Damp proofing materials
The following materials are widely use in damp proofing:
- Flexible materials like butyl rubber , hot bitumen , plastic sheets, bituminous felts, sheets of lead, copper, etc.
- Semi-rigid materials like mastic asphalt
- Rigid materials, like impervious bricks , stones , slates,
- cement mortar , or cement concrete painted with bitumen , etc.
- Mortar with waterproofing compounds
- Coarse sand layers under floors
- Continuous plastic sheets under floors
Methods of damp proofing
- Providing damp proof course: It consists of providing a damp proof course between the source of dampness and building component. The DPC may be with any water repellant material like bitumen, mastic asphalt, cement concrete, metal or plastic sheets. DPC should cover full width of wall. It should be laid on levelled surface of mortar. Joints should be minimum and should not be at critical points. When horizontal DPC on roof is continued on vertical face of parapet wall, the junction should be filled with about 75 mm fillet of cement concrete.
- Providing cavity wall: Cavity wall may be constructed to protect foundation masonry and the wall. The cavity prevents moisture travelling from outer to inner wall.
- Surface treatment: If moisture is only superficial and not under pressure this method is useful. It consists of application of layer of water repellant compounds on the surface. Some of the water proofing agents used for such treatment are silicates of sodium or potassium and sulphates of aluminium, zinc and magnesium.
- Integral treatment: It consists in mixing commercially available compounds in water before concrete is wet mixed. These compounds are made from chalk, talc, flutter earth or chemical compounds like calcium chloride, aluminium sulphate, calcium chloride etc. Some compounds contain compounds like soap, petroleum oils, fatty acids etc.
- Guniting: In this method a mixture of cement and water is forced by cement gun on the surface to be made water proof. Later 1 : 3 or 1 : 4 cement mortar is applied to the surface with pressure using compressed air. Thus an impervious layer of mortar is provided.
- Pressure grouting: This is the method used to seal cracks in the concrete surfaces. In this method cement grout is forced under pressure.