Building

Causes, effect, type & prevention of Dampness in building

 

Aim of this course:

After going through this course, the reader or learner should be able to:

  • Understand what is dampness in building
  • Causes of dampness in building
  • Effect of dampness in building
  • Prevention of dampness in building

What is dampness in building? 

Dampness in building is when excess water molecule is on building which results to visible growth of mould and destruction or disturbance of wall surfaces and materials or it is the access and penetration of moisture content into building through its walls, floor, roof etc.

Causes of Dampness in building:

Dampness in building is caused by the followings:

  1. Rain penetration
  2. Level of site
  3. Waterlogged soil
  4.  Climate condition
  5. Defective orientation of building
  6.  Moisture entrapped during construction
  7. Defective construction e.g. joints
  8.  Use of poor quality bricks which ultimately absorb a lot of water.
  9. Use of Poor quality of concrete (permeable concrete)
  1. Rain penetration: If the roof is not well constructed to take out water rain, it may lead to dampness on walls due to leakages down from roof to wall.
  2. Level of site: This is the higher external ground level around the property. That is when the building level is lower to the road and the surrounding environment.
  3. Waterlogged soil: Moisture in the soil can rise up into the building through capillary action and cause dampness in building.
  4.  Climate condition: When hot humid air comes in contact with materials cooled by the airconditioning process, it causes condensation on the liquid water on the surfaces.
  5.  Defective orientation of building: Indoor activities which releases moisture into the air like cooking, dishwashing, clothes washing, bathing etc.
  6.  Moisture entrapped during construction: Poor quality works when water penetrate through walls can occur as a result of inadequately installed roof covering,improper treatment or covering of oversite concrete.
  7. Defective construction: Leak from bad slate/tile or cracked concrete gutter will increase build up of moisture in walls ,timber and plaster.

Effects of dampness in buildings:

  1. Causes rotting of wood.
  2. Causes corrosion of metallic fixtures.
  3. Deteriorate electric installations.
  4. Deteriorate carpet & furniture’s.
  5. Causes spots on the floors and walls.
  6. Causes petting off and removal of plaster.
  7. Causes bleaching and blistering of paints.
  8. Causes efflorescence in bricks, tiles and stones
  9. Dangerous for the health of occupants.
  10. Reduces the life of structures
  11. Promotes growth of termites

Prevention of Dampness in building:

  1. Introducing damp proof course during construction of foundation especially in waterlogged area.
  2. Using raft foundation mostly in waterlogged area.
  3. proper concrete mix ratio and fine aggregates which helps to make concrete impervious.
  4. Adequate concrete thickness.
  5. Using bitumen on concrete roof surfaces.
  6. Mixing waterproof cement with concrete.
  7. Using breathable paint.
  8. cavity wall construction This is shielding the main wall of the building by an outer skin wall leaving a cavity in between the two. The cavity prevents the moisture from travelling from the outer to the inner walls.

Materials, DPC and Method of Damp proofing

What is Damp proofing Course (DPC)? 

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.

What is 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.

What is Damp proofing in building? 

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.

Damp proofing materials

Materials widely use in damp proofing:

  1. Flexible materials like butyl rubber , hot bitumen , plastic sheets, bituminous felts, sheets of lead, copper, etc.
  2. Semi-rigid materials like mastic asphalt
  3. Rigid materials, like impervious bricks , stones , slates,
  4. cement mortar , or cement concrete painted with bitumen , etc.
  5. Stones
  6. Mortar with waterproofing compounds
  7. Coarse sand layers under floors
  8. Continuous plastic sheets under floors

Methods of damp proofing:

  1. Providing D.P.C.
  2. Providing cavity walls
  3. Surface treatment
  4. Integral treatment
  5. Guniting
  6. Pressure grouting.
  1. 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.
  2. 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.
  3. 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.
  4. 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.
  5. 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.
  6. Pressure grouting: This is the method used to seal cracks in the concrete surfaces. In this method cement grout is forced under pressure.

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