2. • Dampness- presence of hygroscopic or gravitational moisture
- gives rise to unhygienic conditions
• Damp Proofing- a provision to prevent the entry of moisture in the
building
Causes of Dampness
• Moisture rising up the walls from ground
If soil is pervious, moisture constantly travels through it
(sometimes in case of impervious soil also). This moisture may rise into
the wall and floor through capillary action. Ground water rise will also
result in moisture entry into the building through walls and floor.
3. • Rain travel from wall tops
If the walls are not properly protected from rain penetration, rain
will enter the wall and will travel down. Leaking roofs will also permit
water to enter.
• Rain beating against external walls
Heavy showers of rain may beat against the external faces of
walls and if the walls are not properly treated, moisture will enter the
wall, causing dampness in the interior.
If balconies and chajja projections do not have proper outward
slope, water will accumulate on these and could enter the walls
through their junction.
• Condensation
Due to condensation of atmospheric moisture, water is
deposited on the walls, floors and ceilings which may cause dampness.
4. • Miscellaneous causes
poor drainage at building site
imperfect orientation i.e. walls getting less sunlight and heavy showers may
remain damp
imperfect roof slope especially in case of flat roofs
defective construction i.e. imperfect wall jointing, joints in roofs, etc
absorption of water from defective rain water pipes
5. Effects of dampness
• Gives rise to breeding of mosquitoes and create unhealthy living
conditions
• Cause unsighty patches
• Cause softening and crumbling of plaster
• Damage of wall decoration i.e. painting etc. which is very difficult and
costly to repair
• Cause efflorescence resulting in disintegration of bricks, stones, tiles
etc. and consequent reduction in strength
• Flooring get loosened because of reduction because of reduction in
adhesion when moisture enters through floor
6. • Deterioration of timber fittings coming in contact with damp walls or
floors because of warping, buckling, , dry rotting etc. of timber
• Deterioration of electrical fittings giving rise to leakage of electricity
and consequent danger of short circuit
• Damage of floor coverings
• Promotes and accelerate growth of termites
• Causes breeding of germs of dangerous diseases like tuberculosis,
neuralgia etc.
• Causes rusting and corrosion of metal fittings attached to damp walls,
floors, ceilings
7. Methods of Damp Proofing
• Membrane damp proofing/ damp proofing course
This method involves the introduction of water repellent membrane or damp-proof
course between the source of dampness and the part of building adjacent to it.
DPC may be of flexible materials like bitumen, polythene sheets, metal sheets, etc.
DPC may be provided either horizontally or vertically in floors, walls, etc.
DPC should cover full thickness of walls.
mortar bed supporting DPC should be levelled and even, and should be free from
projections, so that DPC is not damaged.
horizontal DPC should be laid continuous at junctions and corners of walls.
DPC should not be kept exposed on the wall surface otherwise it may get damaged
during finishing work.
When a horizontal DPC is continued to a vertical face, cement concrete fillet of 7.5
cm radius should be provided at junction.
8. • Integral damp proofing
This method consists of adding certain water proofing compounds of
materials to the concrete mix, so that it becomes impermeable
Water proofing compounds may be in three forms:
1. Compounds made from chalk, talc, fuller earth, which may fill the voids under the
mechanical action principle
2. Compounds like alkaline silicates, aluminum sulphate, calcium chloride which react
chemically with concrete to produce water proof concrete
3. Compounds like soap, petroleum, oils, fatty acid compounds work on water repulsion
principle. When these are mixed with concrete, the concrete becomes water repellent.
• Surface treatment
This method consists of application of layer of water repellent substances or
compounds on the surfaces through which moisture enters.
The use of water repellent soaps such as calcium and aluminum oletes and
stearates are effective against rain water penetration.
This treatment is effective only when moisture is superficial and is not under
pressure.
9. • Cavity wall construction
In this method, the main wall of building is shielded by an outer skin wall,
leaving a cavity between the two.
One of the effective method of damp protection
• Guniting
In this method, an impervious layer of rich cement mortar is deposited over
the exposed surfaces under pressure.
Cement mortar of 1:3 cement sand mix is shot on cleaned surface with the
help of cement gun under a pressure of 2 to 3 kg/cm2.
The nozzle of machine is kept at a distance about 75 to 90 cm from the
surface to be gunited.
The mortar layer should be cured at least for 10 days.
10. • Pressure Grouting
In this method, cement grout is forced, under pressure, into cracks, voids,
fissures present in structural components of the building or in the ground.
The structural components and foundations which are liable to moisture
penetration are consolidated and thus made water- penetration resistant.
This method is quite effective in checking the seepage of raised ground water
through foundations and sub-structure of a building.
Guniting Pressure Grouting
