MORTAR as Building Material

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The term mortar is used to indicate a paste prepared by adding
required quantity of water to a mixture of binding material like cement or
Lime and fine aggregates like sand. The two components of mortar
namely the binding material and fine aggregates are some times referred
to as matrix the durability, quality and strength of mortar will mainly
depends on quantity and quality of the matrix. The combined effect of
the two components of mortar is that the mass is able to bind the bricks
or stones firmly

Properties – Uses:
The important properties of a good mortar mix are
mobility, placeability and water retention. The mobility is used to
indicate the consistency of mortar mix, which may range from
stiff to fluid
The mobility of mortar depends upon composition of
mortar and mortar mixes to be used for masonry work, finishing
works, etc are made sufficiently mobile.
The placeability or the ease with which the mortar mix
can be placed with minimum cost in a thin and uniform layer
over the surface depends on the mobility of mortar. The
placeablity of mortar mix should be such that a strong bond is
developed with the surface of the bed.

A good mortar mix should posses the ability if retaining
adequate humidity during the transportation and laying over the
porous bed.
If water retention power of mortar mix is low it separates
into layers during transportation and when it comes contact with
the porous bed like brick, wood, etc, it gives away its water to
that surface. Thus the mortar becomes poor in a amount of water
and remaining water proves to be insufficient for its hardening.
Hence required strength of mortar will not be achieved with such
a mortar mix will.

Properties of good mortar

  1. It should be capable of developing good adhesion with the
    building units such as bricks, stones etc.
  2. It should be capable of developing the designed stresses.
  3. It should be capable of resisting penetration of rainwater.
  4. It should be cheap.
  5. It should be durable.
  6. It should be easily workable.
  7. It should not affect the durability of materials with which it
    comes into contact.

Uses:

  1. To bind the building units such as bricks, stones etc.
  2. To carry out painting and plaster works on exposed surfaces
    of masonry
  3. To form an even bedding layer for building units
  4. To form joints of pipes
  5. To improve the appearance of structure.

Types of Mortar
The mortar are classified on the bases of the following

  1. Bulk density
  2. Kinds of binding material
  3. Nature of application
  4. Special mortars

Bulk density:
According to bulk density of mortar in dry state, the mortars are
two types
a. Heavy mortars bulk density is more than 1500kg/m3 and
prepared from heavy quartz
b. Lightweight mortars – bulk density is less than 1500/mg3
and prepared from light porous sands.

Kinds of binding Material
According to the kinds of binding material, several factors
such as expected working conditions, hardening temperature,
moisture conditions, etc should be considered. The mortars are
classified into four categories.
a. Lime Mortar – in this motor, lime is used as binding material.
Lime may be fate lime or Hydraulic lime. Fat lime mortar 1:2 to
1:3 and hydraulic lime mortarmay be1:2 by VOLUME.

b. Cement mortar: In this mortar, cement is used as binding
material. Depending upon the strength required and importance
of work, the proportion of cement to sand varies from 1:2 to 1:6
or more.
c. Gauged Mortar or composite mortar:
The process of adding cement to lime mortar to improve the
quality of lime mortar is known as gauging. It makes lime mortar
economical, strong and dense. The usual proportion of cement to
lime by volume is about 1:6 to 1:8
d. Gypsum mortar:
These mortars are prepared from gypsum binding material such
as building gypsum and anhydrite binding materials.

Nature of Application:
According to the nature of application, the mortars are
classified into two categories.
A. Brick laying mortars: Mortars for brick laying are intended to
be used for brick works and walls. Depending up on the working
conditions and type of construction, the composition of masonry
mortars with respect to the kind of binding materials is decided.
B. Finishing Mortars: these mortars include common plastering
work and mortars for developing architectural or ornamental
effects. Generally cement or lime is used as binding material.

Special Mortars:
A. Fire resistant mortar– This mortar is prepared by adding 1:2
ratio of aluminous cement with crushed powder of fire bricks
used for fire brick lining furnaces, fire places, ovens etc.
B. Light weight mortar – This mortar is prepared by adding
sawdust, wood powder to lime or cement mortar for sound
proof and heat proof construction
C. Packing Mortar – To pack of oil wells, special mortars
possessing the properties of high homogeneity, water
resistance, predetermined setting time, ability to form solid
water proof plugs in cracks and voids of rocks, resistance to
subsoil water pressure etc. have to be formed with cement
sand, cement loam and cement sand loam mortars.
D. Sound absorbing mortars: To reduce the noise level, sound
absorbing mortars with Portland cement, lime, gypsum, slag
Portland cement etc as the binding materials employed in its
composition. The aggregates re selected from lightweight
porous material such as pumice, cinders etc.
E. X-ray shielding mortar: This type of mortar is used for
providing the plastering coat to walls and celling of x-ray
cabinets. This is heavy mortar with bulk density over
2200kg/m3 is used. The aggregates are obtained from heavy
rock and suitable admixture are added to enhance protective
property of such a mortar.

Preparation of cement mortar
For preparing mortar, water is added to intimate mixtures
of binding material and sand. The water to be used for this
purpose should be free from clay, earth and other impurities.
Water which is fit for drinking should only be used for preparing
mortar.
Cement mortar may be prepared by manual mixing or by
mechanical mixing. Mechanical mixing is preferred when mortar
is required in large quantities to be used in continuous order.
a. Mixing in mechanical mixer: In this case, cement and
sand in desired proportion are fed in the mixer and mixed
dry. Water is then added gradually and the wet mixing a
continued for at least one minute to obtain the mortar of
desired consistency. It is necessary to ensure that only the
quantity of mortar which can be used within half an hour of
its mixing should be prepared at a time. This is essential as
after 30 minutes the mortar begins to set.
b. Manual mixing: In this case, specified quantity of sand is
spread and leveled on clean dry masonry platform.
Required quantity of cement bags are emptied over the sand
layer. The ingredients are then mixed thoroughly by turning
them over the sand layer. The ingredients are then mixed
thoroughly by turning them over and over. Backward and
forward several times with the help of spade. Dry mixing is continued till the mix have attains a uniform colour. A batch of dry mix is then put in the shallow masonry tank and just sufficient quantity of water is added to bring the mortar to the consistency of a paste. The quantity of dry
mix taken in each batch should be such the mortar formed
each time is consumed within half an hour.

Precautions in using mortar

  1. Consumption of mortar – the consumption of mortar
    should be as early as possible
    Line mortar – with in 36 hours after its
    preparation
    Cement mortar – within 30 minutes
    Gaged mortar – within 2 hours.
  2. Frost action – Setting action of mortar is affected by the presence
    of frost and not advisable in frosty weather.
  3. Soaking of building units: Building units should not be soaked
    before application of mortar. If this precaution is not taken, water
    of mortar will be absorbed by the building units and mortar will
    become weak.
  4. Sprinkling of water: The construction work carried out by
    mortar should be kept dam or wet by sprinkling water for about 7
    to 10 days to avoid rapid drying of mortar.
  5. Workability: Mortar should not contain excess water and it
    should be stiff as can be conveniently used. Joints should be well
    formed and excess mortar from joints should be neatly taken off
    by a trowel. Surface formed by mortar for building units to rest
    should be even.

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