Clay masonry units are specified in accordance with the required appearance and durability (refer to the summary table at the end of this section).
The required appearance determines whether the units need to conform to C62 or to C216. Under C216, the required dimensional tolerances determine the Type (FBS or FBX).
The required durability and freeze-thaw resistance determine whether the units need to conform to Grade NW, MW, or SW. The required durability and freeze-thaw resistance depend on the weathering index (product of the average annual number of freezing cycle days and the average annual winter rainfall in inches), defined in detail in ASTM C62 and depicted in Fig. 2.4. Negligible weathering regions have weathering indices of less than 50; moderate weathering regions have weathering indices between 50 and 500; and severe weathering regions have weathering indices in excess of 500.
Under ASTM C62 (Building Brick), Grade NW brick are recommended for interior use only. Grade MW brick are permitted for use in severe weathering regions. Grade SW brick are recommended for use in severe weathering regions, and whenever brick are in contact with the ground, or laid in horizontal surfaces, or likely to be permeated with water. Under ASTM C216 (Facing Brick), there are no Grade NW brick. Grade MW brick are permitted for use in severe weathering regions. Grade SW brick are required for use whenever the weathering index is greater than or equal to 500, and whenever brick in other than vertical surfaces are in contact with soil. Requirements of ASTM C62 and C216 for clay units are summarized in Table 2.9.
