TYPES OF MORTARS AND THEIR USES

Mortars using different binding materials have been used for various purposes. These are discussed below.

Lime Mortar

It is the mortar wherein fat lime or hydraulic lime is used as the binding material. The lime should be slaked before use. If fat lime is used, 2–3 times the volume of sand has to be used as it shrinks to a great extent. This lime mortar is not suitable for water-logged areas or in damp situations.

It is easy to handle and is highly plastic in nature. It has high cohesiveness and adheres to the surface and undergoes less shrinking. Although it is sufficiently durable, it hardens slowly. It is suitable for light-loaded structures and is used for construction purposes above the ground.

Surkhi Mortar

It is prepared using lime and surkhi instead of sand. In case of fat lime mortar only 50% needs to be replaced by surkhi. Surkhi should be powdered well.

Surkhi mortar is used for ordinary masonry work. It can not be used for pointing works and for plastering as the surkhi is likely to disintegrate.

7.7.3 Cement Mortar

It is obtained by using cement as the binding material. Cement mortars are assigned certain grades based on their minimum compressive strength at 28 days curing and mix proportion by volume. Some of the grades that are frequently used are given in Table 7.1.

Table 7.1 Cement mortar mix and strength

Note: MM denotes Masonry Cement Mortar.

The recommended cement mortar mix for different purposes are as follows:

1. MM 2 – For external works with protection and foundation masonry in very wet soil.
2. > MM 2 – For external walls without protection.
3. MM 3 – For foundation masonry in soil with saturated water and for masonry subjected to vibrations.
4. MM 5 to MM 7.5 – For plastering.
5. MM 7.5 – For floor finishes and damp-proof courses.

Cement mortar is used for the following purposes:

1. In brick and stone masonry.
2. For plastering of surfaces of structures like walls, beams, columns, etc.
3. For floor finishes.
4. As binding material for decorative and aesthetic works.
5. For pointing of stone or brick masonry works.
6. For irregular surfaces of stone masonry to distribute the load uniformly on the bed.
7. For underground construction purposes, water-saturated soils, etc.

Lime–Cement Mortar

This type of mortar is also called Gauged Mortar or Composite Mortar. It is the one wherein the quality of lime mortar is improved by adding cement to get early strength. This makes lime mortar economical, strong and dense. The general proportion of cement to lime by volume is about 1:6–1.8. This mortar is useful for purposes like bedding and for thick brick walls.

Mud Mortar

Cohesive clay is puddled or pugged with water till the required consistency is attained. In order to prevent shrinkage and cracks, certain fibrous materials are also added. All the ingredients are mixed thoroughly. The life of mud mortar varies from 5–15 years depending on its water-proofing treatment and weather conditions.

Mud mortar has been in use in ancient days and mostly in villages. This can be used for brickwork of ordinary buildings. It is also used for surface floors and plastering internal walls and to some extent external walls also. In order to protect the exposed wall to rain, the mud plaster surface may be sprayed or painted with bituminous material. Instead the bituminous material is mixed in the preparation stage itself so as to add weather-proof properties to the mud mortar.

Fire-resistant Mortar

It is obtained by adding aluminuous cement to the finely ground powder of fire bricks. This is fire-resistant mortar, which can be used with fire bricks for furnace lining, fire places, etc.

Light-weight Mortar

It is obtained by mixing materials like saw dust, wood powder, asbestos fibres, jute fibres, etc., to the lime mortar or cement mortar. This type of mortar is used for sound-proof and heat-proof construction.

7.7.8 Packing Mortar

It is a special type of mortar possessing properties of high homogeneity, water resistance, predetermined setting time and the ability to form solid and water-proof plugs. This property of the mortar is useful for plugging cracks or voids of rocks, resistance to subsoil water pressure, etc., in oil wells. Different kinds of packing mortars are cement–sand, cement–loam and cement–sand–loam.

Sound-absorbing Mortar

This type of mortar is formed by compositioning Portland Cement, lime, gypsum, slag, etc. The crushed aggregates are selected from light-weight porous materials such as pumice, cinders, etc.

X-Ray Shielding Mortar

It is a heavy type of mortar, which is obtained from crushed heavy rocks, and suitable admixtures are added to get the required property. A plastering coat of this mortar is applied to the walls and ceiling of X-ray cabinets.