Workability is the important property of mortar cement.
Mortar cement is the bonding material commonly used for masonry buildings. The quality of its mixing is crucial to its workability. Mortar is comprised of varying proportions of cement, lime, sand and water with optional aggregates such as grit or gravel. A thorough mixing of these ingredients is necessary. A rotating drum-type machine can mix industrial-size amounts of mortar. For hand-mixing, the amount of mortar used should be no greater than the capacity of an average wheelbarrow.
Portland Cement
Portland cement is the most important component of mortar. Its basic composition is limestone and clay that have been ground down to powdered mixture, dried and then.heated in a kiln to between 2,550 and 2,990 degrees. The final product is called clinker and mostly is the compound calcium silicate. This is ground down again and blended with small amounts of gypsum, a form of calcium sulfate. Portland cement hardens when water is added.
Lime
The addition of lime to cement makes it more workable. Lime helps minimize the cracking of set mortar while increasing the strength of its bonding to brick or stone units. The addition of lime also decreases the amount of water required. Minor cracks in lime mortar can seal themselves. Mildly acidic rainwater dissolves some of the lime in the cement and evaporates leaving a calcium carbonate residue. This residue adds to the strength of the mortar and minimizes the amount of moisture that can infiltrate between the mortar and brick joint.
Sand
Sand in mortar cement creates the greater part of the final volume. The air space between sand grains in the mortar creates one third of the final mortar volume. The sand should be clean, free from salts and vegetable matter and evenly graded. The optimal grain size should be like beach sand. A smaller grain size introduces clay grains into the mortar mixture. The clay expands in water giving it a "fatty" effect. This yields mortar that sets slowly, has a low strength and a tendency to crack.
Polymers
Acrylic polymer additions to the cement and sand mixture can be substituted for lime. Polymers improve the workability of the mortar and provide waterproofing. They are more adaptable in domestic applications than lime, and are frequently used as grout and for repairs.
Water
The quantity of water required for a mortar mix depends on the proportions of sand, cement and lime. Increased amounts of sand require increased amounts of water, though in a lower proportion. The water should come from the water main and be free of vegetable matter. Some cement compositions enable seawater to be used. The final mortar mixture should have a workable consistency.
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