ASTRA-GLAZE-SW® + units have been used to construct interior and exterior walls of buildings in almost every part of the continental United States for more than ten (10) years with excellent results. Important Note: As with any building material, it is important that the building design and workmanship be correct. For example, if the units are laid in the wall such that the concrete block substrate is continually saturated with moisture (in the winter months in northern climates) due to inadequate flashing or coping, poor mortar joints, leaking water pipes, etc., then the constant freezing and thawing action can eventually cause crazing. Of course cracking, due to settling or wall movement can also allow large amounts of moisture to enter and saturate the concrete blocks, causing the same problem. Good masonry building practices and workmanship (including well tooled joints) should be specified and enforced.