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Sealing the Contemporary Wall Top

Protecting the top of masonry walls is an important design consideration when detailing masonry buildings. If water is allowed to penetrate the top of exterior walls, the entire wall system can be compromised, leading to efflorescence, deterioration, and eventually, its destruction.

Many types of masonry walls require proper capping, which can extend the life of the wall, minimize maintenance, and contribute to sustainability.

The components of a well-detailed and well-built top of wall are:

  • Stone wall cap with overhang and drip: The cap or coping should be of dense precast concrete, casts tone, or natural stone cap. Brick or any masonry material that requires many individual horizontal joints should not be used as a wall cap. The joints will absorb water and can be subject to the effects from freeze-thaw conditions or simple deterioration from excessive exposure to water saturation. The cap's width should extend beyond the wall about 1½ inches with a formed drip. The cap should also be sloped to allow water to easily flow off the top surface.
  • Metal flashing: Use a strong and durable sheets metal flashing below the cap. The flashing should also have a drip at each end to deflect water away from the wall. Some details call for a less expensive membrane flashing with metal drip edges at the ends of the wall. This detail can lead to problems, as additional lap conditions are required within the wall cap.
  • Anchors s sealed through the flashing: The anchors that secure the stone should be capped and sealed to the surface of the flashing.
  • A solid bearing surface below the cap.
  • A vented air space.
  • Sealant joints: One of the most important elements of a cap detail is the exposed joints. All joints (top surface joints between stone and the horizontal joints between stone cap and flashing) should be filled with mortar, compressed, and then raked back to leave room for a sealant joint. Experience and history have proven that exposed mortar joints will crack and fail, yet designers still insist on specifying mortar joints.
  • Two examples
    Wall caps are needed on exterior walls that end in a parapet above a roof (Figure 1). This detail might be used for an insulated masonry drainage wall ending just above a roof in which the vented air/drainage space is maintained. There are three important points to make. First, the stone coping cap has an overhang of about 1 ½ inches. Second, the coping cap is anchored in a mortar fill that is supported by a mesh restraint. And third, a continuous metal flashing extends the entire assemblage. Figure 2 shows the detail in three dimensions.

    Figure 1 Top of Wall – Stone Cap with Overhang
    Figure 1 Top of Wall – Stone Cap with Overhang

    Figure 2 Top of Wall – Stone Cap with Overhang
    Figure 2 Top of Wall – Stone Cap with Overhang

    Wall caps also protect a simple site wall with an exposed veneer on two sides from potential moisture damage. Air and drainage space is essential in preventing efflorescence, keeping the wall dry and preventing deterioration. As with the vented air wall, it is important to keep a solid filled masonry unit or solid filled grout space beneath the stone cap for support and to provide a surface for a “full” mortar bed.

    Richard Filloramo is Area Director of Market Development and Technical Services for the International Masonry Institute, New England Region's Connecticut office. With more than 35 years of experience, he has been involved with the design, construction, and inspection of more than 5000 building projects. He has created and presented several seminars on masonry.


    You can find more information on these top of wall details on the International Masonry Institute's Web site, IMI is updating and expanding its Masonry Detailing Series to include 2-D CAD details, 3-D animated details, actual jobsite and build photos, and a brief description and live video of the details being constructed. IMI also provides technical representatives to answer questions on these details at 800-464-0988.