What are the industry recommendations for banding dissimilar masonry veneer materials?

ANSWER: 

Often, clay masonry is incorporated into exterior concrete masonry veneer, or concrete masonry is used in clay brick veneer as accent bands. The bands add architectural interest to the wall and can help hide horizontal elements such as flashing and expansion joints. However, combining these two materials within one wythe of masonry requires special detailing due to the different material properties.

When a band of concrete masonry is located within a clay brick veneer, one method of detailing is to place horizontal joint reinforcement in the mortar joints immediately above and below the band. The veneer should be anchored to the backing within 12 inches above and below the band.  Also, anchors should be installed within the band whenever the band consists of more than one course. For bands higher than two courses, joint reinforcement should also be placed within the band itself at a spacing of 16 in. (406 mm) on center vertically. Ideally, the joint reinforcement and ties should be placed in alternate joints so that one does not interfere with placement of the other. Some designers, however, prefer placing joint reinforcement in every bed joint in the concrete masonry band. In this case, a tie that accommodates both tie and wire in the same mortar joint should be used, such as a seismic clip type wall tie. (Refer to Figure 1a in NCMA TEK 05-02A.)

Alternatively, a slip plane can be incorporated into the interfaces between the concrete masonry courses and clay masonry courses to allow unrestrained longitudinal movement between the two materials. This can be accomplished by placing building paper, polyethylene, flashing or a similar material in the horizontal bed joints above and below the band. When hollow masonry units are used for the band, the slip plane below the band should incorporate flashing, so that water draining down the cores of the band can be directed out of the wall at the flashing. When slip planes are used, joint reinforcement should be incorporated into the concrete masonry band in the veneer. The exposed mortar joint at the top and bottom of the band should be raked back and sealed with an appropriate sealant to prevent water penetration at these joints.  If the bottom joint incorporates flashing, however, sealant should not be installed so as to cover the edge of the flashing or the weeps.

When slip planes are used, the veneer should be anchored to the backing within 12 inches above and below the isolated band.  Also, anchors should be installed within the band whenever the band consists of more than one course.  In addition to incorporating joint reinforcement in the concrete masonry, expansion joint spacing should be decreased to reduce the potential for masonry cracking. Experience has shown that vertical expansion joints in the clay masonry veneer should extend through the concrete masonry band as well, and be placed at a maximum of 20 ft (6.1 m) along the length of the wall. Local experience may require reducing the expansion joint spacing from 20 ft to 16 ft.  Although concrete masonry construction typically requires control joints rather than expansion joints, control joints should not be used in the concrete masonry band at the expansion joint locations.  (Refer to Figure 1b in NCMA TEK 05-02A.)ncma-tek-5-2a-fig1.original

The recommendations to control differential movement for clay brick masonry bands in a concrete masonry wythe are very similar to those for a concrete masonry band in clay brick veneer: joint reinforcement above and below the band,  wall ties within the band and wall ties within 12 inches above and below the band. Seismic clip-type wall ties are recommended, as they provide an adjustable wall tie and joint reinforcement in one assembly.  With this construction, it is imperative that the concrete masonry veneer control joints not contain mortar where they extend through the clay brick band, because that would restrict brick expansion.

Cast stone is another material that may be used in feature bands within clay masonry veneer, or vice versa.  When the cast stone units are hand held units that are bedded in mortar, banding of cast stone in clay masonry and banding of clay masonry within cast stone masonry should be treated the same as if the cast stone was concrete masonry.  When large cast stone units are installed with gravity support anchors rather than mortar bedding, the cast stone masonry should be isolated from the clay masonry.

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