Definition of damp
proofing
One of the essential requirements of a building is that it should be dry.
Dampness in building may occur due to bad design, faulty construction and use
of poor quality of materials. Dampness not only affects the life of building
adversely, but also creates unhygienic condition for the occupants. The
treatment given to prevent leakage of water from roof is generally termed as
waterproofing, where as the treatment given to keep the walls, floors and
basement dry is termed as damp proofing.
A damp proof course (DPC) is a physical barrier inserted into the fabric of
a building to stop water passing from one place to another. This can be on a
horizontal plane, stopping water rising up from the ground by being sucked up
by the dry masonry above, or vertically to stop water passing from the outside
of a building, though the masonry, to the inside. DPC's have taken many forms
through the ages and one of the earliest forms was to use a layer of slate in
the construction. Slate is still used but the less expensive plastic version
(below right) is now more widely used.
Horizontal
dpc
Causes of Dampness:
The dampness in building is a universal problem and the various causes,
which are responsible for the entry of dampness in a structure, are as follow.
Rising of moisture from ground
The ground on which the building is construction may be made of soil, which
easily allows the water to pass. Usually the building material used for the
foundations, absorb moisture by capillary action. Thus the dampness finds its
way to the floor through the sub structure.
Rising of grond water level
Action of rain
If the faces of
wall, exposed to heavy showers of rain, are not suitable is protected, the
become sources of dampness in the structure. Similarly the leaking root also
permits the rainwater to enter a structure.
Exposed of top
wall
The parapet wall
and compound wall also should be providing with a damp proof course on the
exposed tops. Otherwise the dampness entering thought these exposed tops of
such walls may lead to serious result.
Condensation
The process of condensation takes place when warm humid air is cooled. This
is due to the fact that cool air can contain less invisible water vapour than
warm air. The moisture deposits on the walls, floors and ceiling. This is the
main causes in badly designed kitchen.
There are various causes of dampness as mention below
1. If the site located on a site, which cannot be easily drained off, the
dampness will be interring in structure.
2. The orientation of a building is also an important factor, the wall obtaining
less sunrise and heavy shower of rain are liable to become damp.
3. The new constructed walls remains damp for short duration.
4. Very flat slope of a roof may also lead the penetration of rain water
which is temporary store on roof.
5. The dampness also caused due to bad workmanship in construction
Such as defective joints in the roofs, improper connection of wall.
Effect of dampness
The building material such as bricks, timbers, concrete etc, has moisture
content, which is not harmful under normal condition. The rise in moisture
content of these materials beyond the certain level from where it come visible
or when it deterioration leads to the real dampness. If absolute terms, the
moisture content of different materials may be same, but the acceptable limit
differs from material to material. For instance, the presence of 10 per cent by
weight in timber is not harmful. But the same level could saturate a brick or
cause deterioration of plaster.
The structure is badly affected by dampness. The prominent effect of
dampness is as follow.
·
A damp building
gives rise to breeding of mosquitoes and creates unhealthy condition for those
who occupy it.
·
The metals used
in the construction of material are corroded.
·
The decay of
timber takes place rapidly due to dry-rot in a damp atmosphere.
·
The unsightly
patches are formed on the wall surface and ceiling.
·
The materials
used as floor covering are serious damaged.
·
It results in
softening and crumbing of the plaster.
·
The materials
used for wall decoration are damaged and it leads to difficult and costly
repairs.
·
The flooring get
loosened because of reduction in the adhesion when moisture enters through the
floor.
Methods of damp proofing
Following methods are used for prevent the defect of dampness in structure
·
Membrane
damp-proofing
·
Integral
damp-proofing
·
Surface
treatment
·
Guniting
·
Cavity wall
construction
Membrane
damp-proofing
This consists in proving layer or membrane of water repellent material
between the source of dampness and the part of the structure adjacent to it.
This type of layer is commonly known as damp-proof course and it may comprise
of material like bituminous felts, mastic asphalt, silicon, epoxy, polymers,
plastic or polythene sheets, cement concrete etc depending upon the source of
dampness, d.p.c may be provided horizontally or vertically in floor, walls etc.
provision of d.p.c in basement is normally term as tanking.
Membrane damp proofing
General
Principles to be observed while laying d.p.c are as under
·
The d.p.c should
cover full thickness of wall excluding rendering.
·
The mortar bed upon
which the d.p.c is to be laid should be made leveled, even and free
projections. Uneven base is likely to cause damage to d.p.c.
·
When a
horizontal d.p.c is to be continued to a vertical face, a cement concrete
fillet 75 mm in radius should be provided at the junction, prior to the
treatment.
·
Each d.p.c
should be placed in correct relation to other d.p.c, so as to ensure a complete
and continuous barrier to the passage of water from floors, walls or roofs.
Integral damp proofing
This consists in adding certain water-proofing compound with the concrete
mix to increase its impermeability. Such compounds are available in market in
powdered as well as liquid form. The compounds made from clay, sand or lime
help to fill the voids in concrete and make it water proof.
Another form of compound like alkaline silicate, aluminum sulphates,
calcium chloride etc. react chemically when mixed in concrete to produce water
proof concrete.
Pudlo, permo, impermo etc are some of the many commercially made
preparations of water-proofing compound commonly used. The quantity of water
proofing compound to be added to cement depends upon the manufacture
recommendations. In general, one kg of water proofing compound is added with
one bag of cement to render the mortar or concrete water-proofing.
Surface treatment
The moisture finds its way through the pores of material used in finishing.
In order to check the entry of the moisture into the pores, they must be filled
up. Surface treatment consists in filling up the pores of the surface subjected
to dampness. The use of water repellent metallic soaps such as calcium and
aluminium oleates and stearates is much effective in protecting the building
against the ravage of heavy rain. Bituminous solution, cement coating,
transparent coatings, paints and varnishes fall under this category. In
addition to other surface treatment given to walls, the one commonly used in
lime cement plaster. The walls plastered with cement, lime and sand mixed in
proportions of 1:1:6 is found to serve the purpose of preventing dampness in
wall due to rain effectively.
Surface treatment
Guniting
This consists in deposing an impervious layer of rich cement mortar over
the surface to be water proofed. The operation is carried out by use of a
machine known as cementgun. The assembly broadly consists of a machine having
arrangement for forcing the mixture under pressure through a 50 mm dia flexible
hosepipe. The hosepipe has nozzle at its free end to which water is supplied
under pressure through a separate connection.
The surface to be treated is first thoroughly cleaned of dirt, dust, grease
or loose particles and wetted properly. Cement and sand usually taken in
proportion of 1:3 to 1:4 are then fed into the machine. This mixture finally
shot on the prepared surface under a pressure of 2 to 3 kg/cm2 by holding the
nozzle of the cement gun at a distance of 75 to 90 cm from the working face.
The quantity of water in the mix can be controlled by means of regulating value
provided in the water supply hose attachment. Since the material is applied
under pressure it ensures dense compaction and better adhesion of the rich
cement mortar and hence the treated surface becomes waterproof.
Guniting
Cavity wall
construction
This consists in 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
traveling from outer to the inner wall.
Cavity wall construction
