The primary purposes of wall rendering mortar was probably to seal walls and provide protection against weathering erosion to maximize durability as well as to provide an aesthetically pleasing appearance. In some cases, a wall rendering mortar must also be able to resist mechanical stress, chemically aggressive environment and extremely heavy moisture loads.
The most importance factor in the fresh mortar mix is to have a superior adhesion property so that when the mix is applied onto the wall, it would not easily drop off from wall onto the floor. Another equally important property is its workability characteristic. Too much water in the fresh mix would give superior workability but would on the other hand affect its adhesion property. Superior workability and adhesion properties are pre-requisites to allow an experienced mason to complete his task faster, easier, getting better coverage for given rendering materials and of course to yield for a better finishing.