Sand in mortar serves the following purpose:
1. Sand in mortar increase the bulk of the mix and hence reduce the cost
2. Sand in mortar prevents excessive shrinkage of the mortar in the course of drying and prevents the cracking of the mortar during its setting.
3. The strength of the proportion with cement or lime can be varied by adjusting the sand.
4. The sand increase the resistance of mortar against crushing.
5. The sand increases the surface area while spreading.
6. The sand improves the setting power.