What are the properties of good mortar?
Adhesion or Bond: It should be capable of developing good adhesion with the building units such as bricks, stones etc.
Durability: It should be able to resist freeze thaw and other environmental conditions.
Resisting penetration of rainwater: The porosity should be tight enough to resist wind driven rains and not shrink allowing the bond between the mortar and masonry unit to separate.
Workability: It should spread easily without the addition of too much water and retain the water to allow for a good bond.