Types of of Mortar as binding material:
The kind of binding material for a mortar is selected by keeping in mind several factors such as expected working conditions, hardening temperature, moisture conditions, etc. According to the kind of binding material, the mortars are classified into the following five categories:
i. Lime mortar
ii. Surkhi mortar
iii. Cement mortar
iv. Gauged mortar
v. Gypsum mortar.
i. 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. 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.
ii. 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. 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".
iii. 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. 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.
iv. 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.
v. Gypsum mortar:
These mortars are prepared from gypsum binding materials such as building gypsum and anhydrite binding materials.