1 Introduction
It is a well known fact ‘A Chain is As Strong As The Weakest Link’. So is the case with the brick masonry or stone masonry which comprises of two units one building blocks such as bricks, blocks etc and other being the mortar or some kind of the binding material. Since, these collectively form the masonry so the selection of the mortar is equally important as the selection of the building block such as brick, AAC blocks etc.
As per CPWD Specifications 2019 Volume1 different types of cement shall not be mixed together. In case more than one type of cement is used in any work, a record shall be kept showing the location and the types of cement used.
2 Selection of Mortar
As per CPWD Specifications 2019 Volume1 the selection of masonry mortars from durability consideration will have to cover both the loading and exposure condition of the masonry. The masonry mortar shall generally be selected as specified below:-
- In case of masonry exposed frequent to rain and where there is further protection by way of plastering or rendering or other finishes, the grade of mortar shall not be less than MM 0.7 but shall preferably be of grade MM 2. Where no protection is provided, the grade of mortar for external wall shall not be less than MM 2.
- In case of load bearing internal walls, the grade of mortar shall preferably be MM 0.702 or more for high durability but in no case less than MM 0.5.
- In the case of masonry work in foundations laid below damp proof course, the grade of mortar for use in masonry shall be as specified below.
- Where soil has little moisture, masonry mortar of grade not less than MM 0.7 shall be used.
- Where soil is very damp, masonry mortar of grade preferably MM 2 or more shall be used. But in no case shall the grade of mortar be less than MM 2.
- For masonry in building subject to vibration of machinery, the grade of mortar shall not be less than MM 3.
- For parapets, where the height is greater than thrice the thickness, the grade of masonry mortar shall not be less than MM 3. In case of low parapets the grade of mortar shall be the same as used in the wall masonry.
- The grade of mortar for bedding joints in masonry with large concrete blocks shall not be less than MM 3.
- While mixing the pozzolanic material like fly ash in mortars Ordinary Portland cement only shall be use.
3 Recommendations on Selection of Mortar
| S.No. | Nature of Work | Type of Mortar |
|---|---|---|
| 1 | Construction work in water logged areas and exposed positions | Cement or lime mortar prop. 1:3 lime being eminently hydraulic lime |
| 2 | Damp-proof courses and cement concrete roads | Cement Mortar prop. 1:2 |
| 3 | General R.C.C. work such as lintels, columns, slabs, stairs etc. | Cement mortar prop. 1:3, the concrete mix being 1:2:4 |
| 4 | Internal walls and surfaces of less importance | Lime cinder mortar prop. 1:3. Sand is replaced by ashes or cinder |
| 5 | Mortar for laying fire-bricks | Fire-resisting mortar consisting of 1 part of aluminous cement to 2 parts of finely crushed powder of fire-bricks. |
| 6 | Partition walls and parapet walls | Cement mortar prop. 1:3 Lime mortar prop. 1:1. Lime should be moderately hydraulic lime. |
| 7 | Plaster work | Cement Mortar prop. 1:3 to 1:4. Lime Mortar prop. 1:2 |
| 8 | Pointing work | Cement mortar prop. 1:1 to 1:2 |
| 9 | Reinforced brickwork | Cement mortar prop. 1:3 |
| 10 | Stone masonry with best varieties of stones | Lime mortar prop. 1:2. Lime being eminently hydraulic lime. |
| 11 | Stone masonry with ordinary stones, brickwork, foundations etc. | Cement mortar prop. 1:6. Lime mortar prop.1:2 Lime should be eminently hydraulic lime or moderately hydraulic lime. |
| 12 | Thin joints in brickwork | Lime mortar prop. 1:3. Lime being fat lime. |
4 References
- IS 2250-1981 Code of Practice for Preparation and Use of Masonry Mortars
- CPWD Specifications 2019 Volume1
- ‘Engineering Materials‘ by Rangwala, Charotar Publications
- ‘Building Materials‘ by S.K.Duggal, New Age International Publishers
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