Why Flashing Matters
Water is masonry’s greatest enemy—and flashing is one of the most important defenses. A well-detailed flashing system directs water out of the cavity and away from the face of the wall, protecting the structural elements, and keep the veneer looking good for decades.
When flashing is missing, poorly installed, or chosen incorrectly, problems multiply quickly: leaks around windows and doors, stained brick, at the bottom of door and window jambs and the callbacks no contractor wants. In short, flashing may be one of the least expensive parts of a project, but it has an outsized impact on long-term performance.
Choosing the Right Flashing Material
Different jobs require different solutions, and flashing materials aren’t one-size-fits-all. Today, flashing membranes provide masons with reliable, easy-to-install options. MortarFlash® from Mortar Net Solutions (the masonry division of Keene Building Products) offers a full line, including each of the following:
- Peel-and-stick membranes – Easy to apply and self-sealing, good for irregular surfaces. Substrate preparation is critical. Peel-and-stick membraned comprise three groups, they are as follows:
- Rubberized asphalt – Flexible and reliable, rubberized asphalt has many advantages and a cost that is typically very economical.
- Non-asphaltic membranes –reliable and easy to work with. This product is stable under UV and temperature extremes. Sealant compatibility should be matched to the specific product to ensure adhesion.
- EPDM flashings – Cost-effective for concealed locations, Very easy to use Ethylene Propylene Diene Monomer (EPDM) is flexible under all working temperatures and is easy to install on irregular surfaces. Typically, EPDM is sealed using butyl, non-curing synthetic rubber BTL-1.
- Metals (stainless steel, copper, galvanized steel) – Extremely durable with puncture resistant facers typically used on long lasting projects.
Pro tip: Match flashing type to exposure, budget, and substrate. Saving a few dollars per foot on material often costs thousands in repairs later.
Windows and Doors: Common Trouble Spots
Openings in veneer walls are the number-one place for leaks.
Sill flashing should be placed one to two courses below the sill to prevent veneer cracking. WeepVents or CellVents should be placed in the veneer flashing under the sill. It is important to always use end dams bonded into the head joint of your veneer. Always include a drip edge.
- Head flashing above windows should be placed and bonded to the structural lintel. End dams and CellVent or WeepVents should be placed at 16-inch increments.
- Jambs should be protected with transition membrane. Placement of the tape should begin at the bottom of the wall and shingled at the seams.
- Terminations Bars should be mechanically secured with termination bars and sealed. Using TEK screws tightened snug to the substrate.
Field reminder: Flashing must integrate with air and vapor barriers. A perfect piece of flashing doesn’t work if water can sneak behind it.
Mortar Shelf Flashing and Weep Holes
Cavity walls are designed to drain. For that to happen, the mortar shelf flashing (base flashing) and weep holes must work together.
Mortar droppings can clog the base of the cavity above flashings. Devices like MortarNet™ with Insect Barrier suspend mortar droppings above flashing, keeping drainage paths open while blocking pests.
Getting Transitions Right
Flashing is best when the proper components are consistently used. Components found at the termination of flashings are very important to install correctly.
- End dams and corner boots prevent water from running off the end of flashing.
- Roof-to-wall intersections need counter-flashing and sealed overlaps.
- Foundation-to-wall areas should include base flashing and proper grading to slope water away.
- Parapets and coping details should use durable, UV-resistant flashings with secure terminations.
Pro tip: Always inspect flashing before covering it. Once the brick is laid, mistakes are sealed in.
Common Mistakes to Avoid
- Choosing the wrong flashing for exposure conditions.
- Omitting end dams or corner components.
- Reverse laps that drive water inward.
- Applying material to a dirty or wet substrates that prevent adhesion.
- Weep holes placed incorrectly spaced or omitted.
These aren’t design flaws, they’re field mistakes. Careful installation practices and on-site quality control make the difference.
Pro Tip: Always slope flashing outward. If water can’t drain away, it will find a way in.
Conclusion
Flashing is a small detail that carries big responsibility. Flashing may be one of the least expensive parts of a wall, but it’s the single most important detail for keeping masonry dry.It keeps water where it belongs—outside the building—and protects the structure for decades.
Whether you’re using stainless steel, peel-and-stick membranes, or a PVC option, the keys are always the same: slope outward, extend beyond the veneer, integrate with barriers, and inspect before covering. Products like MortarFlash® give masons reliable tools, but success depends on execution in the field.
For masons and contractors, mastering flashing isn’t optional; it’s essential to delivering durable, watertight masonry that stands the test of time.
