2. Dampness a common
problem in buildings.
It refers to access and
penetration of moisture
content
into buildings through its
walls,
floors, roof etc.
It is important to take measures to prevent dampness.
Such measures is called damp proofing.
Water proofing is a treatment of the surface or structure in a building to
prevent leakage.
3. Moisturefromground:-Thematerials usedfor thefoundationand floorsabsorbmoisture
fromthesoil andit rises up the surfaceof the building,
Splashingof rain:-Whenrainsplashes on external walls dampness may enter the interior.
Exposedtop wall:-dampnessenters fromthe top if the topsof parapet walls are not given
sufficient dampproofingcourse.
Condensation: dampnessis causeddue to condensationof atmospheric moisture, deposited
on wallsand ceilings.
Constructiondefects:-
Improperplanning,
lackof proper slope in roof,
defective pipefittings,
improperlysealedconstructionjoints
are constructive defects.
4. Ugly patches on walls and ceilings.
Plaster softens and crumbles.
Materials used for wall decorations are damaged.
Stones ,bricks and tiles disintegrate due to efflorescence.
Floor finish may be damaged
Woodworks decays due to dry rot.
Metal components of building corrodes.
Electrical fittings are damaged,
Dampness leads to
breeding of mosquitoes, growth of
termites and germs carrying
diseases such as tuberculosis,
it also aggravates asthma.
6. Hot bitumen :-hot bitumen,3mm thick may be applied on
bedding of mortar or concrete.
Mastic asphalt:-semi rigid material obtained by heating asphalt
with sand and mineral fillers. It is laid on mortar or concrete
bed.
Bituminous felt:-flexible material available in rolls. It is laid on
flat mortar finished surfaces.
Metal sheets:-sheets of lead, copper and aluminum may be
used membranes in damp proofing. Lead is the most ideally
suited material.
7. Combination of sheets and felts:-economical and drable damp
proofing sheet is obtained by sandwiching a lead sheet and
bituminous felt.
plastic sheets:-a relatively cheap method
of damp proofing is by laying 0.5-1.0mm
thick plastic sheets made of black
polythene. This is not a permanent method.
Bricks:-quality bricks absorbing water less than 4.5% of their
weight may be used for damp proofing. These bricks are laid in 2-
4 courses in cement mortar.
Mortar:-cement mortar in the ratio 1:3 is used for bedding layers
over damp proofing course. It may be mixed with slaked lime to
improve its workability.
Cement concrete course:-a cement concrete course of proportion
1:2:4 and thickness 75-150mm is laid on masonry at plinth level.
8. General principles to be followed in damp proofing
are:-
Mortarbedpreparedto receivedamp-proof courseshouldbe leveled.
Thehorizontaldamp proofing courseshould coverthe fullwidthof wallexcluding
rendering.
If sheetsor masticasphaltare used, the gap shouldnot be lessthan100mmat any point.
At jointsand corners. Damp proof courseshould be continuous.
Dampproofingcourse shouldnot be kept exposedon the wall surface.
At verticaland horizontaljunctions, damp proof courses shouldbe continuousand a
cement mortarfillet of about 75mm shouldcover joints.
9. Different types of treatments are used for preventing dampness in diff
parts of the building:-
Foundations:-this is method of protecting foundations of
outer walls. An air drain is constructed parallel to the
wall.
The drain is covered with
RCC slab, and gratings are
provided at regular intervals,
horizontal and vertical damp
proof courses are also provided.
10. Treatment for floors:-
if there is no damp soil, a layer of coarse sand,75-100mm
thick is provided over entire area under the flooring. Then
1:4:8 concrete of 100mm thickness is laid. This layer serves
as DPC. the usual flooring is provided over this,
If soil is wet, a membrane DPC is provided over the floor
area, over
which
a layer of flat bricks
is laid.
The usual flooring is
then provided.
11. Treatment for walls:
the plinth level should preferably be 450mm above ground
level.DPC should be provided over a concrete bed of thickness
100-200mm.the top of the parapet should be provided with
capping over the DPC. the wall also needs DPC at the edge of
the roof slab.
12. Providing foundation drains and DPC:-
to release hydrostatic pressure,trenches are made all around the
building and filled with gravels etc. such trenches may also be required
in buildings if the water table is at a higher level. The trenches lead the
water to a catch drain.Horizontal and
vertical DPCs are provided in
the walls and foundation concrete.
13. Providing RCC raft and wall slab:-
if the water pressureis high, providinga drainagesystemwill not solvethe problemeffectively. In suchcasesthe
floorslabandwall may be preparedright throughthe RCC structure and DPCis appliedon it.
14. Asphalt tanking:-
also known as membrane waterproofing.
Construction of horizontal layers :a leveled course of mass
concrete is laid for the flooring area ,over which a 30 mm
thick DPC in form of asphaltic layer is provided a protective
layer of cement screed, concrete or a layer of brick work is
laid over the asphaltic
layer, after which the
flooring is prepared.
15. constructionofverticalface:-
A vertical DPC is provided on the external face of
the wall. The DPC consist of an asphalt layer of about 20mm built in
three coats. This is then protected with a wall of ½ brick thickness.
16. Lime concrete terracing:-
The RCC roof is cleaned thoroughly and a
bitumen primer is applied ,3 coats of hot blown asphalt is then applied over which a specially
prepared lime concrete bed of 100mmthickness is provided. The surface of bedding is covered
with flat tiles. a convex corner
joint is made at the junction
with the parapet wall.
17. Membrane water proofing:-
water proofing membrane may be prepared with mastic asphalt or plastic
sheet. It is provided in a number of layers from 2-7.in this method a layer
of hot mastic asphalt is applied on the clean roof surface. This is
covered by jute cloth and another layer of mastic asphalt is laid.
In case of plastic membranes, hot coating is applied with blown bitumen
between each layer. The top is usually finished with a course of flat
tiles.
At the junction is properly sealed with the parapet. The membrane
should extend up to parapet or lead sheets should be inserted.
18. Water proofing compounds may be grouped to 2:-
Waterproofing admixtures:-these admixtures are in powder or liquid
form. About 2% of powders are mixed while making cement mortar.
when the finishing coat of mortar is provided, these compounds seal
the pores in the slab and make
them watertight.
19. Waterproofing membrane system:-these
materials are available in the form of paints,
they may epoxy or elastomeric and may be
applied to roof slabs with rollers ,brush or
spray. a minimum of 2 coats are applied to
get desired waterproofing.
20. Sloped RCC roofs are provided with tiles for purpose of weather proofing. It is
preferable to use flat tiles fixed to roof.
If Mangalore tiles are used care should be taken. continuous motor bands should not
be provided as reapers because in case rainwater entering through broken tiles
stagnates on the mortar bands, leakage will occur. Hence mortar bands supporting
Mangalore tiles should be discontinuous. before laying the tiles, the possible leakage
points should be checked and identified.
