Dampness is a common problem in buildings, which refers to the access and diffusion of moisture content into houses through its walls, floor, roof, etc.
The aim of the construction is to offer an impermeable boundary in order that the capillary action is destroyed. Dampness not only weakens the structure of the building but also harms the health of the inhabitants.
It is crucial to take measures to avoid dampness during the process of constructing the buildings. These measures are known as damp-proofing.
Sources of Dampness
Construction defects: Factors like improper planning of drainage, defective pipe fittings, improperly sealed construction joints, insufficient proper slope in a roof are in charge of dampness.
Condensation: Dampness is also caused because of the condensation of atmospheric moisture, which is stored on walls and ceilings.
Moisture content from the ground: The materials used for the building blocks and floors absorb moisture content from the soil, and spreads up to the top of building by capillary action.
Rain water accumulated on the Rooftop
Splashing of rain: The accumulated water during raining enters the walls and causes dampness.
Exposed top of wall: If the top of the parapet is not supplied with proper damp proofing, then it causes dampness.
Effect of Dampness
The effect of dampness causes the following outcomes:
Rough patches start appearing on the walls and ceiling.
Plaster on the walls weakens and crumbles.
Metal components of the building corrode, and electrical fittings get damaged.
Effect of dampness on the walls
Woodwork decays and the materials used for wall decorations such as paints and wallpapers are damaged.
Stones, bricks and tiles deteriorate due to efflorescence that is the appearance of a white, pale substance that sticks to the stone or concrete walls when water steeps through.
Dampness leads breeding of mosquitoes, growth of termites and germs that carry diseases like tuberculosis and asthma.
Materials for Damp proofing
Flexible materials such as bituminous materials, plastic sheets, metal sheets of copper, lead, etc.
Semi-rigid materials like mastic asphalt and rigid materials like impervious bricks, stones, slates, cement mortar or cement concrete painted with bitumen etc.
Bitumen material for damp proofing course
Mortar and Cement concrete with damp proofing compounds, coarse sand layer and continuous plastic sheets under floors are also used for damp-proofing.
Principles of rising damp
The common principles in damp-proofing are the following:
The damp-proofing course should not be kept open on the top of wall.
The lap should not be less than 100 mm at any point if sheets or mastic asphalt materials are being used for damp proofing.
Damp proofing course should be continuous at joints and corners.
The mortar bed ready to receive a damp-proof course should be levelled on the top.
The damp-proof courses should be continuous at vertical and horizontal junctions, and a cement mortar fillet around 75 mm should cover the joints.
Methods of Damp proofing
There are different types of treatments used to avoid or prevent dampness in different elements of the building, and they are simply mentioned as follows:
Foundations
An air drain of 200 – 300 mm is constructed parallel to the wall to safeguard the foundations of outer walls. Horizontal and vertical damp – proof courses are also directed at foundations, and the drain is covered with RCC slab, and gratings are given at regular intervals.
Damp proofing for Foundations
Treatment for floors
A layer of coarse sand, 75 – 100 mm thick is provided over the complete area under the flooring which serves as DPC. If soil is wet, a membrane DPC is provided over the ground area which bricks are laid and then usual flooring is provided above it.
Damp proofing for Floors
Treatment for walls
Walls should be protected from dampness at plinth level, and also near the top of the parapet. The plinth level should be 450 mm above ground level and shouldn’t be lower than 150 mm at any condition.
Damp proofing for Walls
The top of the parapet should be provided with capping within the DPC over a concrete bed of thickness 100 – 120 mm and also wall needs DPC at the edge of the roof slab.
