Definition:
Mortar is a paste prepared by adding required quan- tity of water to a mixture of binding material like cement or lime with sand. The binding material and sand or fine aggregate are, sometimes referred as matrix and adulter- ant. The durability strength and quality of mortar mainly depend on the quantity and quality of the matrix. The combined effect of the two components of mortar is able to bind the bricks or stone family.
Properties of Mortar:
1. It should have good adhesion with bricks, stones etc.
2. It should be in a position to develop the desired stresses in it.
3. It should offer good resistance to the penetration of rain water.
4. It should be cheap and durable.
5. It should be in position to maintain its original appearance for sufficiently long periods.
6. It should be easily workable.
7. It should not adversely affect the building on which it is to be used.
8. It should set and harden quickly, so that speed of constmetion work may be maintained.
9. It should not crack in joints
Types of Mortar:
The kind of binding material for amortar is selected by keeping in mind several factors such as expected work- ing conditions, hardening temperature, moisture condi- tions, etc. According to the kind of binding material, the mortars are classified into the following categories:
● Surkhi mortar
●Cement mortar
●Gauged mortar
●Gypsum mortar.
● Surkhi mortar: using fully surkhi instead of sand or by replacing half of sand in case off. mortar. The powder of surkhi should be fine enough to IS Sieve No. 9 and the residue should not be more than 10% by weight.The surkhi mortar is used for ordinary masonry work of all in foundation and superstructure.
● Cement mortar: In this type of mortar, the cement act as binding material. Depending upon the strength required and importance of work, the pro- portion of cement to sand by volume varies from 1:2 to 1: 6ormore. It should be noted that surkhi and Lime mortar are not chemically insert substances and hence they cannot be used as adult with matrix as cement.The proportion of cement with respect to sand should be determined with due regard to the specified dura- bility and working condition. Cement mortar is used where a mortar of high strength and water-resisting properties is required such as underground construc- tions and water salt soils, etc.
● Gauged mortar. To improve the quality of lime mortar to achieve early strength, the cement is some- times added to it This is known as the gauging. It makes lime mortar economical and strong dense. The usual proportion of cement to lime by volume is about 1:6 to 1:8. Itis also known as the composite mortar or lime-cement and it can also be formed by the combination of cement and clay mortar may be used for bedding and for thick brick walls.
Preparation of Cement Mortar
This mortar does not require pounding or grinding. The The cement and sand are mixed in required proportions in mixing in dry state is done twice or thrice. The water is then added and the ingredients are again thoroughly mixed.
Uses of Mortar :
1. In masonry for binding, the stones or bricks together.
2. To provide a hard, smooth covering surface for wall and floors etc.
3. To form an even bed for the stones or bricks or bro- ken stones in a structure and thus to distribute the super incumbent weight uniformly.
4. Used to joint the pipes.
5. To conceal the defective workmanship and also to till up the joints and cavities and thus to make the wall weather tight.
6. As a matrix in concrete for holding the broken stones together and to form into a solid mass.
7. To improve the appearance of a structure in general.
Precautions in using Mortar
Following precautions are to be taken while making use of mortar:
1. After preparation, the mortar should be consumed as early as possible. The cement mortar should be con- sumed within 30 minutes after adding water and for this reason, it is advisable to prepare cement mortar of one bag of cement at a time.
2. The setting action of mortar is affected by the pres- b ence of frost.
3. The presence of water in mortar is essential to cause its setting action.
4. The construction work carried out by mortar should C be kept damp or wet by sprinkling water to avoid rapid drying of mortar.
5. The mortar should not contain excess water and it should be as stiff as can be conveniently used.
