Masonry Magazine May 1972 Page. 15
quacy is achieved by application of the same design and construction criteria used with standard masonry units. Provision to accommodate differential movement needs consideration because wall cracking due to thermal or moisture movement, while it may not be structurally serious, would be detrimental to the appearance and possibly weathertightness. Wall movement is controlled by horizontal reinforcing steel and/or control joints. Horizontal steel, either in bond beams or as joint reinforcement increases the tensile resistance of the wall. Control joints reduce restraint by accommodating movement. They are vertical separations built into the wall where cracking may occur due to excessive horizontal stress. Location and spacing of control joints will depend upon length and height of wall, amount of horizontal reinforcement, and extent and location of sections of stress concentrations such as windows, doors, and chases. Table 1 presents recommended spacing for control joints in walls with no openings, taking into consideration length and height of wall panel and amount of horizontal reinforcement. Other locations for control joints include (1) Changes in wall height or thickness, (2) at construction joints in foundation, roof and floors, (3) at chases, recesses and columns, (4) at return angles in "L", "T", and "U" shaped structures, and (5) at one or both sides of wall openings. A typical control joint for use with customized unit is illustrated in Figure 2.
Another important detail involves controlling or excluding moisture from the masonry wall. Proper installation of a permanent flashing material is recommended at points where the masonry wall is vulnerable to moisture penetration. Wall flashing is installed to collect moisture that may penetrate the wall and divert it to the exterior, generally through weep holes. Points where masonry walls are vulnerable to moisture are at grade line, sills and heads of openings, spandrel beams and at parapet walls. Requirements will vary for areas of different rainfall and wind pressures; and where exposure is slight, internal flashing, such as lintel or sill flashing may be eliminated. Typical flashing details are shown in Figure 3.
Staining, particularly on light-colored surfaces, can destroy the appearance of an otherwise attractive structure. In some buildings staining can be noticed below sills where concentrations of dirty water, washed from windows and wall areas above is deposited. Other sources of staining include rust deposits where metal brackets, vents, railings, etc. are attached to the wall. Staining of the type described above can be prevented by considering a few simple details. Sills and other projections should be carried out at least 1" from the face of the wall and should be provided with a drip notch or groove on the underside to keep the water from running back under the sill and down the face of the wall. Metal devices
Recommended Spacing of Control Joints
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Vertical Spacing of Joint Reinforcement
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