INTRODUCTION

The cementing materials discussed in the previous chapters can not be used directly as a construction material unless they are combined with some other inert material like aggregates. Thus, a combined material formed by mixing intimately a binding material (cement or lime) with a fine aggregate (sand or surkhi) in a certain proportion and with an adequate quantity of water is called mortar. Here lime or cement enables a proper bond to be developed among the particles, and sand adds mechanical strength to the mortar.

The properties of binding materials, lime and cement, have been discussed at length in the previous chapters. Hence, it is necessary to know more about the fine aggregate and water to be used to get the best mortar.

Properties of mortar and their kinds along with the quality of sand and water to be added are discussed in the following sections.

7.2 QUALITIES OF SAND FOR MORTAR

Sand particles are small soil grains of silica. As per the Indian Soil Classification, particles of diameter greater than 0.075 mm and less that 4.75 mm are categorized as sand.

Sand is naturally available and may be classified as (i) pit sand, (ii) river sand and (iii) sea sand. Sea sand is not suitable for mortar.

For the purposes of mortar, sand is classified as fine, coarse and gravelly sand. Fine sand is one that passes through a screen with clear openings of 1.59 mm, coarse sand passes through a screen with clear openings of 3.18 mm and gravelly sand passes through a screen with clear openings of 7.62 mm. Fine sand is used for plastering, and coarse sand is used for masonry work.

The properties of sand required for mortar are as follows:

1. It should be free from any organic matter.
2. It should be chemically inert.
3. It should be well graded.
4. The fineness modulus of sand should be between 2 and 3.
5. It should be sharp, angular, coarse and clean.