The proposed Standard Practice provides construction tolerance requirements for the appearance of unit masonry. This practice includes three categories of construction tolerance requirements (Categories S, X, and N). These categories are based solely on the desired appearance of masonry exposed to view and the maximum dimensional tolerances of the units used in constructing the masonry. The categories of construction tolerance requirements are appearance requirements that are not intended to be associated with durability or resistance to water penetration. Category S construction tolerances are the set of requirements intended for standard masonry construction. These construction tolerances are appropriate for use with units having dimensional tolerances suitable for Categories S. Category S construction tolerances include variations typical in masonry and are intended to provide an assembly with a handcrafted character that is historically associated with masonry. Category X construction tolerances are the set of requirements intended for precision masonry construction. These construction tolerances are appropriate for use with units having dimensional tolerances suitable for Categories X. Category X construction tolerances include smaller variations for the purpose of achieving an assembly with an aesthetic appearance that is more rigid and uniform than standard construction tolerances. Category N construction tolerances are the set of requirements intended to produce characteristic aesthetic effects. These construction tolerances are greater than Category S construction tolerances either because the maximum permissible dimensional tolerances of the units exceed the maximum variations for Category S or greater dimensional tolerances are desired for aesthetic effects.
Architects, Engineers, and Specifiers typically include requirements for construction tolerance of unit masonry for appearance in their project documents. The tolerance requirements included in many architectural specifications are taken from Master Spec and other specification references. Often, these requirements are too tight to be achieved in actual construction either because the specified tolerances exceed the tolerances of the units themselves or they are not practical to be met by the mason. This can result in unrealistic expectations that may lead to rejection of completed masonry or litigation. This standard is being developed to provide a reasonable, consensus document (based on input from mason contractors, the International Masonry Institute, designers, and several industry associations) that can serve as a reference for architects, engineers, and specifiers. Although there are construction tolerances contained within the MSJC document, these tolerances are generally limited to items that affect the structural performance of masonry rather than appearance. As a result, they include some tolerances that do not affect appearance and omit other tolerance requirements that should be included.
Keywordsconstruction tolerance; dimensional tolerance; masonry; masonry units; mortar joints; non-uniform; precision; standard
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