SYSTEMS/MASONRY
Materials
The materials of masonry construction have been studied for many years, and the properties
necessary for good performance are well established (see BIA Technical Note 21, NCMA-TEK
No.85 and the PCA Concrete Masonry Handbook for more information). Quality materials are
necessary to achieve good performance, and even the best design and construction will be
compromised by poor materials. The materials of concern include the masonry units, mortar,
coatings, ties and anchors, flashing, shelf angles, and joint materials. Specifications for many of
these materials have been developed by ASTM and other organizations. Masonry unit
specifications include strength, durability and water absorption, and provide guidance on the
selection of units based on climate and anticipated loads. Specifications for masonry units are
provided in ASTM C 55 (concrete building brick), C 90 (hollow load-bearing concrete masonry), C
129 (non-load-bearing concrete masonry) and C 145 (solid load-bearing concrete masonry). The
important material properties of mortars include workability, water retentivity, strength, adhesion
and durability. The various types of mortars and their properties are described in ASTM C270 and
C476 for nonreinforced and reinforced masonry respectively. Additional material requirements
exist for clear or opaque coatings used to provide watertightness or water resistance. The
materials properties of ties, anchors, shelf angles, flashing and joint materials relate to strength,
durability and corrosion resistance.
Crack Control
Cracking of masonry walls obviously impacts water and air leakage, and can lead to more serious
problems of structural integrity for facades or whole walls. Grimm published a literature review of
masonry cracking in 1986; the issue is also covered in BIA Technical Note 18 and NCMA TEK No.3
and No.53. Cracking occurs when the inevitable movement of building materials is restrained by
the material itself or by adjacent elements. Such movement is caused by a variety of forces
including temperature expansion and contraction, changes in moisture content, and structural
loads. The differential movement of building components can be anticipated and must be
accommodated for in design, otherwise cracking will result. Cracking can be controlled by the
specification of materials that limit moisture-induced movement, the use of reinforcement such as
bond beams, and the use of control joints or other devices to accommodate movement. In masonry
veneer walls, the design of shelf angles that can accommodate movement is of particular
importance and is described in Grimm and elsewhere. Crack control must be a part of the design of
masonry walls, otherwise cracks will develop and both water leakage and air leakage will increase.
As discussed in the section on water leakage, some fine cracking is inevitable, e.g. at mortar-unit
interfaces, and adequate means must be provided for the drainage of the water that leaks through
these cracks.
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