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Lapping and sealing. At the base of the wall, through-wall flashing must be uninterrupted. At the joints and corners of a house, the flashing should be lapped at least 6 inches and sealed. This is easily done if you're using self-adhesive rubberized asphalt flashing. Otherwise, consult the flashing manufacturer for recommendations regarding the proper mastic or lap cement (Figure 6).

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Figure 6. If the flexible flashing is not one of the self-adhering types, use mastic to seal any overlaps.

Note that some flashings react with certain mastics, drastically affecting the performance of the flashings. Extend the flashing at least to the front face of the brick. Although the BIA recommends that the flashing should extend 1/4 inch beyond the brick face and turn down to form a drip, some of the flexible flashing materials can deteriorate when exposed to the weather. One solution with self-adhesive flashing is to install a metal drip in conjunction with the flexible flashing. If the flashing is installed sloppily - short of the face of the brick - then the collected water won't be delivered to the exterior. Remember, the core holes are typically only 3/4 inch back from the face. Even if care is taken to ensure that the flashing projects no less than 1/2 inch from the face of the wall, the flashing can scoot back when mortar and brick are laid over it, allowing water to enter the cores of the brick (Figure 7). Image

Figure 7.

This flashing has been installed incorrectly, since it does not extend all the way to the front face of the brick. Any water is directed into the core holes of the brick instead of to the exterior. Because of these problems, many installers extend the flashing well past the face of the brick until the wall is complete, then cut the flashing flush with the face of the masonry. According to the BIA, this practice is acceptable, although it is not recommended.