As an architect, should I specify Grade SW Type FBX clay masonry units to get the most durable units available?
The durability of a clay masonry unit is related to its grade. The grade and type of clay masonry units are defined in ASTM C 62, C 216, and C 652. Grade SW (or severe weathering) is the most durable classification of brick. Grade MW units are less durable and can be used for face brick in parts of the country where the weathering index is not as severe. Grade NW brick are the least durable and they generally are used only on interior work. Type FBX has nothing to do with the unit's durability. Type is an indication of a unit's mechanical tolerances. Type FBX allows a very narrow color range and only minimal size variations. These units are used where a very uniform appearance is desired. Type FBS units are more common. These units offer a wider range of color and size variations. Type FBA units are used to create special architectural effects. These units have no limits for size and color variations.