Portland cement mortar is unnecessarily strong and concentrates any differential movement within brick -work or blockwork into a few large cracks, which are unsightly and may increase the risk of rain penetration.
Masonry cement produces a weaker mortar, which accommodates some differential movement, and ensures a distribution of hairline cracks within joints, thus preserving the integrity of the bricks and blocks . Masonry cements contain water-retaining mineral constituents, usually ground limestone or hydrated lime, and air-entraining agents to give a higher work -ability than unblended Portland cement. They should not normally be blended with further admixtures but mixed with building sand in ratios between 1 : 2.5 and 1 : 6.5, depending on the type of mineral constituent
and on the degree of exposure of the brick or blockwork.
The air entrained during mixing increases the durability and frost resistance of the hardened mortar. Masonry cement is also appro priate for use in renderings but not for floor screeds or concreting. It is therefore generally used as an alternative to Portland cement plus hydrated lime or plasticiser. Inorganic pigments, except for those containing carbon black,
may be incorporated for visual effect. The strength classes for masonry cements conforming to BS EN 413–1: 2011 .