A glazed brick consists of a clay body, coated with a ceramic material that fuses to the clay when fired at high temperature. The glaze may be clear, translucent, or opaque; glossy or matte; and almost any color. Glazed brick extends the already broad aesthetic range of brick masonry, but it has to be specified and installed with extra care. The glazed finish can chip, crack, or spall; and unless glazed brick masonry is detailed and built properly, it can exacerbate problems associated with water penetration. INTERIOR APPLICATIONS When using glazed brick for interior walls that won't be exposed to the weather, your only real limits are imagination and budget. ASTM C 126 is the standard specification for glazed brick. It defines Grades S and SS, based on permissible variations in face dimensions, and Types I and II for single- or two-faced units. It also sets requirements for compressive strength, dimensional tolerances, and various properties of the finish--imperviousness; opacity; surface burning characteristics; and resistance to fading, crazing, and abrasion. EXTERIOR APPLICATIONS Specifying glazed brick for exterior use involves a number of additional factors because the masonry is exposed to the weather. You need to consider the durability of the brick itself and the weather-resistance of the wall system as a whole. So for exterior walls, you should specify glazed brick that also meet the applicable requirements of ASTM C 216. Because glazed surfaces are particularly vulnerable to freeze-thaw damage, you should always specify brick that meets the durability requirements of Grade SW (severe weathering).