Question: I would like the projecting end of through-wall masonry flashing to match the color of my aluminum curtain-wall system. Can prefinished aluminum flashing with a Kynar 500 finish be used in masonry walls?
- In most cases, there should not be a problem. The Brick Institute of America in Technical Notes 7A warns against the use of aluminum flashing. It states that the high pH of fresh unhardened mortar will attack the aluminum. This usually is not a problem with prefinished aluminum flashing more than 0.040-inch thick. The Kynar 500 finish will resist the caustic alkalies present in the mortar. Also, in many applications, masonry is laid directly on the flashing without mortar beneath the units. Thus the mortar only contacts the flashing at head joints. Even if small scratches occur in the finish, the chemical corrosion will occur only where bare aluminum contacts wet uncarbonated mortar. Mortar generally carbonates very quickly at such an interface. If there will be limited contact with mortar and if a durable and alkali-resistant coating like Kynar 500 is used, there should be no problem with using aluminum flashing in masonry walls.Where there will be substantial mortar contact, use a two-piece flashing as shown in the figure. Bonding a flexible flashing to the surface creates an additional separation between the wet mortar and the aluminum.Where aluminum flashing is used at shelf angles or above other metals, coat the bottom or otherwise separate it to prevent galvanic corrosion.