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Types of Mortar as Binding Material

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The different type of mortars used in the construction as binding material are lime mortar, surkhi mortar, cement mortar, gauged mortar and gypsum mortar. The selection of type of mortar depends on the factors such as working conditions, hardening temperature, moisture conditions, etc. In this article we study about different type of mortars that are used as binding material in construction.

Types of Mortar as Binding Material

Based on the major ingredient of mortar, they are divided as follows,

1. Lime Mortar

In this type of mortar, the lime is used as binding material. The lime may be fat lime or hydraulic lime. The fat lime shrinks to a great extent and hence it requires about 2 to 3 times its volume of sand. The lime should be slaked before use.

Fig 1: Lime Mortar.

This mortar is unsuitable for water-logged areas or in damp situations. It possesses good  cohesiveness with other surfaces and shrinks very little. It is sufficiently durable, but it hardens slowly. It is generally used for lightly loaded above-ground parts of buildings.

Types of Lime Mortar

  1. Hydraulic lime sets by hydration (the addition of water).
  2. Non-hydraulic lime sets by carbonation (through exposure to the air)

Uses of Lime Mortar with Cement

  1. Increased flexural bond strength.
  2. Prevents water leakage
  3. High durability
  4. More compressive strength
  5. Uniformity

2. Surkhi Mortar

This type of mortar is prepared by using fully surkhi instead of sand or by replacing half of sand in case of fat lime mortar. The powder of surkhi should be fine enough to pass BIS No. 9 sieve and the residue should not be more than 10% by weight.

Fig 2: Surkhi Mortar

The surkhi mortar is used for ordinary masonry work of all kinds in foundation and superstructure. But it cannot be used for plastering or pointing since surkhi is likely to disintegrate after some time".

3. Cement Mortar

In this type of mortar, the cement is used as binding material. Depending upon the strength required and importance of work, the proportion of cement to sand by volume varies from 1:2 to 1:6 or more. It should be noted that surkhi and cinder are not chemically inert substances and hence they cannot be used as adulterants with matrix as cement.

Fig 3: Cement Mortar

Thus the sand only can be used to form cement mortar. The proportion of cement with respect to sand should be determined with due regard to the specified durability and working conditions. The cement mortar is used where a mortar of high strength and water-resisting properties is required such as underground constructions, water saturated soils, etc.

Types of Cement Mortar

As per ASTM Specification C-270 , cement mortars are divided into 3 types,
  1. Type N Cement Mortar
  2. Type S Cement Mortar
  3. Type M Cement Mortar
Table 1: Recommended Guide for Selection of Mortar Type as per ASTM Specification C-270
Building Segment Mortar Type
Exterior, above grade,
  load-bearing N or S or M
  non load-bearing N
  parapet wall N or S
Exterior, at or below grade S or M
Interior
  load-bearing N or S
  non load-bearing N

 Desirable properties of good cement mortar

  1. Mortar should possess is adhesion. Good mortar should provide good adhesion to building units (bricks, Stones etc).
  2. Mortar should be water resistant. It should have the capability of resisting the penetration of water.
  3. Deformability of mortar should be low.
  4. Mortar should be easily workable in the site condition.
  5. The mobility of mortar should be good. It helps the mortar to be paved thinly and evenly.
  6. It should possess high durability.
  7. To improve the speed of construction, good mortar should set quickly.
  8. Cracks should not be developed in the joint formed by mortar. It is desirable to last for long period of time without losing the appearance.

4. Gauged Mortar

To improve the quality of lime mortar and to achieve early strength, the cement is sometimes added to it. This process is known as the 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. It is also known as the composite mortar or lime-cement mortar and it can also be formed by the combination of cement and clay. This mortar may be used for bedding and for thick brick walls.

5. Gypsum Mortar

These mortars are prepared from gypsum binding materials such as building gypsum and anhydrite binding materials.

Fig 4: Gypsum Mortar

Read More : 20 Types of Mortar Used in Masonry Construction
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