Masonry cements are hydraulic cements designed for use in mortar for masonry construction. They are composed of one or more of the following: Portland cement, Portland cement – pozzolan cement, Portland blast – furnace slag cement, hydraulic lime, and natural cement. In addition, usually contain materials such as hydrated lime, limestone, chalk, calcareous shell, talc, slag, or clay.

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Materials are selected for their ability to impart workability, plasticity, and water retention to masonry mortars. Masonry cements meet the requirements of ASTM C-91, which classifies masonry cements as Type N, Type S, and Type M. A brief description of each type follows;

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Type N masonry cement is used in ASTM C-270 Type N and Type O mortars. It may also be used with Portland or blended cements to produce Type S and Type M mortars.

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Type S masonry cement is used in ASTM C-270 Type S mortar. It may also be used with portland or blended cements to produce Type M mortar.
 

Type M masonry cement is used in ASTM C-270 Type M mortar without the addition of other cements or hydrated lime. The workability, strength, and color of masonry cements stay at a uniform level because of manufacturing controls. In addition to mortar for masonry
construction, masonry cements are used for parging and plaster (stucco); they must never be used for making concrete.