Water and aggregate for the mortar of above-ground unreinforced masonry, nominally reinforced masonry where vertical joints in adjacent courses are aligned [see Article 9.20.9.1.], loadbearing masonry of buildings of more than one storey in regions where the spectral response acceleration S_a(0.2) is greater than 0.55 that are reinforced in accordance with Sentence 9.20.1.2.(1), and loadbearing masonry of 3-storey buildings in regions where the spectral response acceleration S_a(0.2) is greater than 0.35 and less than or equal to 0.55 that are reinforced in accordance with Sentence 9.20.1.2.(2), used in the construction of buildings to which Part 9 applies [see Sentence 1.3.3.3.(1) of Division A for application of Part 9]:

• where the wall height above the foundation wall does not exceed 11 m, and
• in which the roof or floor system above the first storey is not of concrete construction.

Exceptions: 

To limit the probability of inadequate compressive or bond strength, which could lead to cracking at mortar joints and inadequate bonding to masonry units.

This is to limit the probability of:

• compromised structural integrity of masonry construction,
• where masonry construction is part of an environmental separator, the displacement or failure of required environmental separation elements, which could lead to deterioration, or
• in assemblies exposed to moisture or the exterior, damage and deterioration.

For floors and elements supporting floors, this is to limit the probability of excessive movement, deflection or vibration, which could lead to negative effects on the psychological well-being of persons.