Dampness and Its Prevention
CAUSES OF DAMPNESS
Dampness may
be caused by:
(a) Ground
water
(b) Rainwater
and
(c) Leakages
from pipes.
(a)
Dampness due to Ground Water: All buildings are founded on soils. Soil
holds water for along time. Sometimes water
level may rise and come in contact with foundation. Due to capillary action
moisture from ground rises into foundation, floor and even in wall.
(b) RainWater: May enter the building components due to
various reasons.
(i) From wall top: If top of wall is not protected with
impervious course like concrete,
water can enter the wall
and keep it damp for a long time.
(ii) From face
of external walls: Splashing of outer wall by rain results into moisture
entering the wall. Poor plaster coat is the main source of this type of
dampness.
(iii) Improper
fixing of downtake pipes: If downtake pipes from roof are not properly
fixed, a thin layer of water
stagnates near the mouth of downtake pipes.
This results into entry of rain water into roof and wall.
(iv)
Improper slopes
to roof: In
flat roofs, many times this is the cause for the dampness of roofs. If slope is
not given properly, water ponds are formed on the flat roof, which results into
entry of water into slab. Once water enters the slab it remains for long time
creating dampness.
(v) Defective
construction: Imperfect
wall joints, improper slopes to chejja,
construction joints in roof etc. cause dampness in buildings.
(c) Leakage
from Pipes: From over head tanks, pipes are taken over roof and along
the wall. From bathrooms, toilets and kitchen water is drained out with
different types of pipes. The pipes are joined to get required length and
turns. Many times water leaks through joints resulting into moisture in
building components.
ILL-EFFECTS
OF DAMPNESS
Ill-effects
of dampness are as listed below:
1. Patches
develop and destroy the appearance of the building.
2. Colour
wash, white wash and paintings are damaged.
3. Plaster
crumbles.
4. Bricks and
stones disintegrate endangering the building.
5. Steel in
the slabs and beam start rusting. It reduces the life of structure.
6. Electric
short circuits may takes place.
7. Flooring
may settle.
8. Floor
covers are damaged.
9. Wooden
components of buildings like door frames, cupboard warp.
10. Dry
rotting of wood takes place.
11. Termite
becomes active and attack wooden articles.
12. Mosquito
breeding takes place.
13. Darkness
along with warmth and darkness breed germs giving rise to many diseases.
REQUIREMENTS
OF AN IDEAL MATERIAL FOR DAMP PROOFING
The
requirements of an ideal materials for damp proofing are:
1. It should
be impervious.
2. It should
be flexible.
3. It should
be easy to carry out leak proofing joints.
4. It should
be stable.
5. It should
be durable. It’s life should be as much as
the life of building itself.
6. It should
resist the load safely.
7. It should
not contain sulphates, chloride and nitrates.
8. It should
be cheap.
MATERIALS
FOR DAMP PROOFING
The materials
used for damp proofing are:
1. Bitumen: In hot condition it is
highly flexible and can be applied with brush to the bedding of concrete or
mortar. Thickness of coat provided is about 3 mm.
2. Mastic
asphalt: It
is a semirigid material. It is obtained by
heating asphalt with sand and mineral fillers. It is perfectly impervious. It
should be laid very carefully.
3. Bituminous
or asphaltic felt: It is a flexible material which is available in rolls. It is
provided on roof slabs and parapet walls with an overlap of 100 mm on sides.
The laps are sealed with bitumen. They do not withstand heavy movements.
4. Bricks: Good bricks with
water absorption less than 5 per cent are sometimes used to make damp proof
courses. The bricks are laid in two to four courses in cement mortar.
5. Stones: Stones like
granite, trap and slates may be laid over wall to its full width as damp-proof
course.
6.
Mortar: Cement
mortar of proportion 1 : 3 with small
quantity of lime and water proofing agents are used to make a water proofing
course to foundations, ground floor slabs, top of parapet walls etc. It may be
used for plastering external walls.
7.
Concrete: To
check the rise of water into walls a course of 75 mm to 100 mm cement concrete
1 : 1x1/2 : 3 or 1 : 2 : 4 is provided before starting constructing walls.
These courses may be provided with hot bitumen paint as an additional
precaution.
8. Metal
sheets: Aluminium,
copper or lead sheets are provided to seal the construction joints. Over these
sheets bituminous seal is provided.
9. Plastic
sheets: Plastic
sheets are very good course for damp proofing. They are made up of black
polythene of thickness 1 mm.
METHODS
OF DAMP PROOFING
Various
methods of damp proofing are as given below:
1. Providing
D.P.C. course
2. Providing
cavity walls
3. Surface
treatment
4. Integral
treatment
5. Guniting and
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, cementconcrete, 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.