Masonry Magazine October 2006 Page. 23
Brick Industry Association
FLASHING
FLUE LINER
BACKER ROD
AND SEALANT
CONCRETE CROWN
liner and extended down the outside to lap the first piece of flashing, as shown in Figure 3. For further information on chimney crown flashing, refer to Brick Brief "Proper Chimney Crowns."
OPTIONAL ANCHOR
BRICK CHIMNEY
Figure 3-Flashing at Chimney Crown
Flashing Materials
The use of quality flashing materials cannot be overemphasized. The initial cost is money well spent to avoid costly future repairs. For flashing chimneys, metal flashings are recommended because of their resistance to high temperatures and exterior exposure. The Brick Brief "Through Wall Flashing provides more detalled information on flashing materials.
Copper
Copper is durable, able to withstand elevated temperatures in the chimney, available in special performed shapes, and is an excellent moisture barrier. Copper can be safely embedded in fresh mortar and will not deteriorate in continuously saturated, hardened mortar unless excessive chlorides are present. Copper flashing may stain the concrete crown or brick masonry.
Stainless Steel
Stainless steel is an excellent flashing material. It provides a good water barrier, high-temperature resistance, and has excellent chemical resistance. ASTM A 240, Type 304 should be specified. The minimum thickness used should be 0.01 inch (0.25 mm).
Galvanized Steel
The life of galvanized steel flashing depends on the thickness of the zinc coating, However, thicker coatings may crack when folding the flashing. Galvanized steel is not recommended.
Aluminum
The alkalis present in fresh mortar will attack aluminum. Thus, aluminum should not be used as a flashing material in brick masonry.
Flashing Details and Installation
While flashing is essential to good performance of brick masonry, proper detailing and construction is of the utmost importance. Flashing that stops short of extending through a wall is little better than no flashing at all. It is important that flashing penetrating a wythe of brick extend fully to the outside and form a drip. Flashing and counter flashing must be adequately lapped such that water cannot get behind the inner layer to enter the interior of the structure. Furthermore, flashing must be continuous. Any bends or breaks must be completely sealed. Special, pre-formed shapes that minimize the cutting necessary are available for problem areas such as outside corners.
The Brick Industry Association's "Brick Briefs are short discussions of a particular topic. The information contained herein is based on the experience of Brick Industry Association technical staff and must be used with good technical judgment. Final decisions on the use of this information must rest with the project designer and owner. For more information, please visit www.gobrick.com.
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October 2006
Masonry 21