Masonry Magazine March 2012 Page. 32
MOISTURE MANAGEMENT
tight joints. Also, sheet metal is not flexible. Fishmouths often occur at top vertical edges of the metal if the substrate is not perfectly straight. Additionally, lengths of sheet metal are often limited to sections that can be placed on a truck and delivered to the project site, therefore, more joints are usually required.
Copper fabric flashing
THESE ARE composite products where thin (3-, 5-, or 7-oz) copper sheets are laminated within bituminous products, paper facers, or other proprietary fabrics. They provide many of the benefits of sheet metal as stated above. The bituminous versions can be directly adhered to a variety of substrates in compatible mastic. Joints in the material can easily be formed, lapped, and sealed in mastic. Copper fabric is also flexible enough to conform to irregular substrates.
The bituminous versions cannot be exposed to direct sunlight, so the material cannot extend past the face of the masonry and form a drip. Therefore, a separate sheet metal drip is required.
Rubberized asphalt membranes
THESE SELF-ADHERING "peel-and-stick" membrane sheets are usually 40 mils thick and consist of rubberized asphalt bonded to a polyethylene film. A disposable release liner is provided on the exposed portion of the rubberized asphalt and is removed just prior to adhering the membrane. These membranes are flexible and can be formed around many penetrations. Cutback mastics and asphalt-blended polyurethane liquid membranes are used to seal penetrations. Masonry and wood substrates must be primed and the material should be installed wrinkle-free. Membranes designed for use in wall systems should be specified. Membranes designed for use as waterproofing materials can have asphalts with lower softening points, and the asphalt can flow off the backing film in the hot environment within an exterior wall.
Flexible composite flashing
THESE ARE COMBINATIONS OF various materials and are relatively new to the market. The compositions are similar to copper fabric flashing in that they exploit the advantages of each material. Many composite flexible flashings are sold in rolls of various widths between 12 and 48 inches. Roll lengths can be up to 300 feet. The variety of dimensions allows the material to be unrolled along the length of shelf angles and other long flashings, avoiding laps and joints in the flashing materials.
One such flexible composite flashing system is a combination of a proprietary ketone ethylene ester (KEE) polymer membrane with a pressure-sensitive adhesive. The 40-mil composite membrane has a release paper and is installed in the same manner as a self-adhered flashing. Another product is a vinyl ethylene film bonded to fiberglass reinforcement. This material is most often used with separate metal drip edges and is typically loose-laid and mechanically fastened to the substrate or set in mortar joints of the backup masonry. Special tapes and mastics are used to seal terminations and penetrations.
Typical Flashing Locations
FLASHINGS are more common in drainage cavity and single-wythe walls. However, in the author's opinion, they can be just as important in thicker walls. The following descriptions and figures are generic in nature and should be modified and adapted for use in each particular building by a qualified design professional.
Base of walls
THIS IS PROBABLY the most common location that blocks the downward flow of water within a masonry wall. Locations where rising walls are constructed directly over occupied portions of a building are particularly vulnerable to water infiltration.