I want to use 3-ounce copper flashing with asphalt-impregnated paper bonded to both sides. Several sources recommend that the flashing be extended out past the face of the wall with sealant between the bottom of the flashing and the top of the brick wall below. What sealant can I use to bond to the asphalt-impregnated paper?
Through-wall masonry flashing should always project beyond the face of the masonry, so that water reaching the flashing can exit the wall. When this flashing occurs at a shelf angle with a soft joint beneath, sealant should be applied between the bottom of the flashing and the top of the brick wall below. I know of no sealant, however, that will bond to the asphalt-impregnated paper and still provide adequate movement capabilities. Even if bond is achieved, movement can cause the paper to delaminate. The same problems exist when using copper flashing with polyethylene or kraft paper bonded to it. I recommend using a metal edge strip. The flashing can be bonded to the top surface of the metal edge strip. Sealant can be applied between the metal edge strip and the top of the brick below. In this way adequate bond can be achieved. There is a second advantage with using this detail. In the future when the sealant must be cut out and replaced, the metal edge strip prevents the knife from cutting the flashing. The metal edge also is more durable when exposed to weather than many of the laminated flashings.