Even though mortar makes up as little as 7% of the total volume of a masonry wall, it plays a crucial role in the performance of the structure. It not only bonds the individual units together, but it also seals the building against moisture and air penetration. It can be used to bond to anchors, ties or reinforcing. The mortar is literally the glue that holds the wall system together.
The primary ingredient in mortar is portland cement. Since portland cement is also used in concrete, we need to make a few distinctions here. Concrete is formulated to become a solid monolithic wall system aby itself. The most important characteristic of concrete is compressive strength. Mortar, on the other hand, is formulated to bind masonry units together. The most important qualities of mortar are bond strength and durability. There are several properties of mortar that can influence bond strength and durabilty.

Properties of Mortar:
   Plastic (wet) mortar
       Workability
       Water retentivity and flow
   Hardened mortar
       Bond strength
       Compressive strength