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Good Construction Practices Part II
This report is solely for the internal use. No part of it may be
circulated, quoted, or reproduced for distribution outside the
company organization without prior written
approval from ACC Limited. This material was used during an oral
presentation; it is not a complete record of the discussion.
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Very necessary for strength and durability of concrete
structure
Do not start plastering before completion of Brickwork
curing.
Curing
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By Hessian Clothes for columns & sides of beams
Ponding on flat horizontal surface.
Curing
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Curing
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Strength and Curing
moist cured entire time
in air after 3 days
in air after 7 days
Strength
100%
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time
in air entire time
in air after 3 days
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All bricks should be of same size and color Bricks should be
properly baked. If a brick is dropped from a height of 1 m, it
should not break.
How to choose Bricks?
Brickwork
Correct Practice:
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Bricks should be immersed in water at least two hours before
use. Cement to sand proportion should be 1:5. Use the Mixed
material within half n hour of mixing, otherwise it start loosing
strength. Maximum 1 m work should be done in a day. All joints
should be raked properly.
Correct Practice:
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Mortar and Plaster
Even though mortar makes up as little as 7% of the total volume
of a masonry wall, it plays a crucial role in the performance of
the structure.
It not only bonds the individual units together, but it also
seals the building against moisture and air penetration. It can be
used to bond to anchors, ties or reinforcing.
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The mortar is literally the glue that holds the wall system
together.
The primary ingredient in mortar is Portland cement. Since
Portland cement is also used in concrete, we need to make a few
distinctions here.
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Mortar
Concrete is formulated to become a solid monolithic wall system
by itself.
The most important characteristic of concrete is compressive
strength.
Mortar, on the other hand, is formulated to bind masonry
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Mortar, on the other hand, is formulated to bind masonry units
together.
There are several properties of mortar that can influence bond
strength and durability.
The most important qualities of mortar are bond strength and
durability.
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Requirements of mortar
The single most important property of mortar is bond
strength,.
It is critical that this bond be complete, strong, and
durable.
The mechanical bond between individual bricks, blocks, or stones
unifies the wall as a system, provides resistance to tensile
stress, and seals against the penetration of
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tensile stress, and seals against the penetration of
moisture.
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Factors affecting mortar properties
The strength and extent of the bond are affected by many
variables of material and workmanship.
Complete and intimate contact between the mortar and the unit is
essential,
Workability influences the ease with which the mortar spreads
and covers the surfaces.
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spreads and covers the surfaces.
Rough units have a very porous surface that is highly receptive
to the wet mortar and increases adhesion
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Factors affecting mortar properties
The moisture content and suction of the units, the
water retention of the mortar.
Curing conditions such as temperature, relative
humidity, and wind combine to influence the
completeness and integrity of the mechanical and
chemical bond.
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Voids at the mortar-to-unit interface offer little
resistance to water infiltration and facilitate
subsequent disintegration
In aligning the masonry, laboratory tests show that
tapping the unit to level will increase bond strength
50 to 100% over hand pressure alone
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Factors affecting mortar properties
Often overlooked is the size/shape of mortar joints in
that the ultimate compressive load capacity of a typical
3/8 in. bed joint will probably be well over twice the
value obtained when the mortar is tested as a 2 in.
(50.8 mm) cube.
Mortars should typically be weaker than the masonry
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Mortars should typically be weaker than the masonry
units, so that any cracks will occur in the mortar joints
where they can more easily be repaired.
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Factors affecting mortar properties
Compressive strength of mortar increases with an increase in
cement content and decreases with an increase lime, sand, water or
air content.
Retempering is associated with a decrease in mortar compressive
strength.
The amount of the reduction increases with water addition and
time between mixing and retempering.
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and time between mixing and retempering.
It is frequently desirable to sacrifice some compressive
strength of the mortar in favor of improved bond, consequently
retempering within reasonable time limits is recommended to improve
bond.
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RCC Band at 1 m height which should be of 4 thick with two bars
of minimum 8 mm
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Avoid corner windows in Load bearing structures
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Surface Preparation
Before plastering concrete surface should be hacked properly (
Minimum 50 per sq.ft.)
It is advisable to apply a base coat of cement paste on concrete
surface, and cure it for three days to have a better bonding .
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days to have a better bonding .
A brick wall should be made wet a day before plastering
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The surface to be plastered should be accurately positioned
overall and zones should not deviate excessively from a plane (or
curved) surface.
Ideally, the substrate should be rough; absorbent to a limited
extent; strong; and clean, i.e. free of any film, such as dust, oil
or paint, that could impair bond between plaster and
substrate..
Roughness improves adhesion by providing a positive
Surface Properties required
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Roughness improves adhesion by providing a positive key for
plaster to grip. Absorption removes the water film, between
substrate and plaster, that would tend to weaken adhesion.
Excessive absorption will however dry out the
The strength of the substrate material should be greater than,
or equal to, that of the hardened plaster.
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Surface Preparation
Background surfaces should ideally be at least as rough as
coarse sandpaper or rough-sawn timber.
Surface roughness can be achieved in one of the following
ways:
Using formwork with a rough surface,
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Using formwork with a rough surface, Stripping formwork early
and wire brushing concrete
Hacking Abrasive blasting (e.g. sand blasting) Applying a
spatter dash layer
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Surface Preparation
Spatter dash is a mixture of one part of cement to one and a
half parts of coarse sand with enough water for sluggishly pourable
consistence.
The mixture is thrown forcibly on to the wall, using a scoop or
a brush with long, stiff bristles. (The impact drives out the water
film at the interface between spatterdash and substrate and hence
improves adhesion.)
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The Spatterdash should cover the substrate surface completely
and form a rough texture with nodules about5 mm high.
Spatterdash must not be allowed to dry out for at least three
days.
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Absorption
Assess absorptiveness by throwing about a cupful of water
against the surface.
The surface will fall into one of the three categories:
No water is absorbed. Some water is absorbed but most runs off.
Most of the water is absorbed.
First type of surfaces, include hard-burnt clay face bricks,
glazed bricks and very dense high-strength concrete,
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glazed bricks and very dense high-strength concrete, should be
prepared by applying a spatter dash
Second type of surfaces should not require any treatment to
control suction.
Third type of surfaces should be wetted thoroughly and then
allowed to become surface dry before the plaster is applied.
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Surface - Monolithic concrete.
Provide a rough surface by using rough-textured formwork, early
stripping of formwork and wire brushing the concrete,
hacking or abrasive blasting. (If none of these is practicable,
apply a spatter dash coat after ensuring that the surface is
clean.)
Ensure that no form-release oil is left on the surface to be
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Ensure that no form-release oil is left on the surface to be
plastered. Clean down by water jetting or vacuuming.
Conventional structural concrete should not require wetting to
control suction. High-strength concrete may require the application
of a spatter dash coat.
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Surface - Brickwork
Burnt clay brickwork
If the surface is dusty, clean by brushing, water jetting Burnt
clay stock bricks normally have a very high suction; pre-wet the
wall and allow it to become surface dry before applying the
plaster.
Sun dried or poorly burnt soft clay brickwork
This type of walling may be found in very old buildings,
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This type of walling may be found in very old buildings, usually
when restoration or repairs are being done.
Care should be taken when removing the old plaster so as not to
damage the bricks. Protect the wall from rain water once the bricks
are exposed.
Rake out the joints about 10 mm deep (the mortar is normally
very soft).
Brush down the wall to remove any loosely adhering material.
Lightly dampen the wall and apply a spatter dash coat that
improve adhesion.
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Very Smooth Surface Result in to Poor Bonding.
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Use Bonding agent Or Hack the surface at close spacing
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Surface making.
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