Q. Which flashing is best?

A. We like to give generic advice whenever possible but I do have some preferences. Do NOT use any flashing with vinyl in it. The high pH of wet mortar eats holes in vinyl. This eliminates any PVC flashing products from my recommended list. According to Architectural Graphics Standards, mortar is also corrosive to pure aluminum and pure zinc. Alloys with these materials do not seem to have trouble with corrosion. I recommend metal flashings only for the longest lasting buildings (like cathedrals and university buildings). Although the metal flashing is slightly more expensive than flexible flashings, the time required to cut it, fold it and weld it accounts for the real price jump between flexible flashings and metal ones. Flexible bitumen flashings are my personal favorite for Colorado’s climate. The material is cost effective, easy to
work with, long lasting and tolerant of the high pH of mortar. The tar coating will
even self-heal small holes and cracks once the sun comes out and heats the wall.
The manufacturers tell you to peel off the backing and install the flashing sticky-side down on a clean, dry substrate. You must also hold the flashing back 1/2” from the face of the wall so that the sun doesn’t melt the tar and have it drip down the face
of the building. If you want the flashing to continue to the face of the wall, you can either pair the bitumen flashing with a 1” wide galvanized metal drip edge or you can use Hyload flexible flashing, a bitumen-based flexible flashing system that comes with an integral drip edge. Go to their web site at www.hyloadflashing.com to see more.