The term “brick masonry” can conjure up different images depending on one’s experience: perhaps the yellow brick road in “The Wizard of Oz” or the third little pig’s robust brick masonry home that withstood the Big Bad Wolf’s huffing and puffing. But when managing facilities with brick masonry construction, an understanding of the particular masonry is needed to select appropriate repair and maintenance procedures.

Brick masonry in its simplest form is brick units joined together with mortar. The properties of both the brick units and the mortar can vary for different eras and applications, but it is generally accepted that standard brick units are made from clay, and mortar is made from a combination of cement, water and sand. Therefore, brick masonry is porous and expected to absorb water.

This image shows through wall flashing with weeps, but no end dams at the limits of the flashing. You can tell vertical end dams were not provided as the flashing ends in the middle of a brick unit not at a mortar joint.Knowing the difference

There are two main types of brick masonry walls: cavity walls and mass masonry walls. A cavity brick masonry wall has an outer wythe (a vertical section of masonry one unit thick) of brick masonry serving as the exterior wall, an interior wall constructed of brick, CMU, metal studs or another material, and (as the name suggests) a cavity between the two that may or may not be insulated. Masonry ties are used to link the sections together into one wall system, though whether the outer wythe resists loading or transfers loads back to a structural inner wythe depends on the specific wall’s design. A multi-wythe or mass masonry wall, conversely, is comprised of multiple wythes of brick masonry tied together with “header” bricks, which are brick units that have been rotated perpendicular to the plane of the wall. These header bricks span between wythes while being incorporated into each to interlock them together into a wall system.

These wall types differ greatly in how they process water. A cavity wall allows bulk water to run down its face. If water is absorbed into or otherwise infiltrates the exterior wythe, the wall system relies on the cavity to manage moisture. The cavity, when sized appropriately, can limit the transfer of moisture to the interior wall as it encourages infiltrating water to fall to the base of the cavity where flashings and weeps direct it out of the wall system. Waterproofing is installed on the outer face of the interior wall so water that does reach this point will run down the face of the waterproofing to the base of the cavity where flashings and weeps direct it out of the wall system.

Mass masonry walls allow bulk water to run down the face of the wall and some water to be absorbed through the face of the outer wythe of brick masonry into the masonry itself. The masonry then “dries out” after the precipitation event by returning this moisture to the air. The thickness of the multi-wythe masonry wall is what limits the potential for water to be transferred through the full depth of the wall into the interior of the building.

It’s what’s on the inside that counts

Whether cavity or mass masonry construction, almost all walls have penetrations that will need to be considered as part of the water management system. Windows, doors, pipe penetrations, expansion joints and the like provide openings in the wall system, and as such, provide potential paths for moisture infiltration. Perimeter sealants and through wall flashings with weeps can help manage potential moisture infiltration at penetrations.

Through wall flashings require thoughtful design and installation to serve their intended purpose. If the flashing is laid flat instead of slightly sloped to direct water out of the wall system, standing water can collect on top of the flashing and potentially reach a depth that can flow over the vertical leg of the flashing and back into the wall. If weeps are not provided or are not spaced close enough to serve as a path for moisture to be expelled, similar standing water can result.

If end dams are not provided at the horizontal limits of the flashing, then moisture captured on this flashing plane can move laterally into the wall beyond the limits of the flashing. If flashing seams are not lapped and sealed, then water can work its way between adjacent sections and travel into the wall below the flashing. If the through wall flashing does not extend beyond the exterior vertical plane of the wall with a drip edge to direct water expelled from the flashing away from the wall, the flashing can accelerate deterioration of the masonry directly below it. This is because without extension of the flashing beyond the wall any water expelled from the flashing will run down the face of the masonry below, exposing this area to more bulk water than the rest of the wall. Excess water draining directly onto the masonry below also has the potential to be absorbed back into the wall or, under certain conditions, to result in staining of the lower masonry.

Selecting sealants

Sealants within a masonry wall must also be thoughtfully selected, properly installed and regularly maintained. A backer material should be installed in the joint prior to sealant installation. Depending on the joint configuration this backer material could be a backer rod, which is a foam rod sized to be in compression when installed within a joint, or a bond breaker tape adhered to the substrates. In either case, the intent of the backer material is to avoid three-sided adhesion of the sealant as this can result in premature failure when tensile and/or compressive forces acting on it from multiple directions overstress the sealant. The sealant itself is then installed over the backer material. During initial design/installation, urethane or specific silicone sealants are frequently used in masonry joints. However, during repairs/renovations, if silicone sealant is removed from the joint, it should be replaced with new silicone sealant to encourage proper adhesion. ASTM C920 – Standard Specification for Elastomeric Joint Sealants provides several different classifications for joint sealants to assist with material selection. Sealants can be single component (type S) or multi-component (type M). They can also be classified as non-shrink (grade NS), and given a class (class 100/50, 50, 35, 25, etc.) depending on the capacity for cyclic expansion and contraction. Different uses are provided to identify where a sealant is suitable. For example, for areas with pedestrian and vehicular traffic uses, T1 and T2 are selected depending on the desired hardness, whereas use NT is suitable for nontraffic areas. And depending on the substrate(s) to which the sealant is designed to adhere, the designer would choose a particular use (use M for mortar, G for glass, A for aluminum and O for other). Sealants suitable for multiple substrates will have multiple uses listed, which can be helpful for conditions such as a window perimeter where sealant would need to adhere to both the window frame and the surrounding masonry. Sealants should be reviewed regularly and replaced when adhesive or cohesive failures are identified as failed sealant joints provide a path for bulk water infiltration. In addition to sealants, as part of ongoing maintenance the brick masonry units, mortar joints and flashing weeps within a masonry wall system should be regularly monitored and repaired as needed.

Weeps should be kept clear of debris or replaced if they become too obstructed. to the untrained eye, weep openings meant to expel water from the wall can look like openings through which water can enter the wall system. Consequently, with the best of intentions, these are often sealed/infilled with sealant, spray foam or whatever else is on hand to try to limit moisture infiltration. Instead of preventing water infiltration, however, sealing weeps can trap moisture within the wall, which may eventually find its way into the building interior.

A word on masonry

Recommended maintenance of the brick masonry and mortar includes replacing cracked or spalled brick units, repointing deteriorated or open mortar joints, rebuilding step cracked masonry, and repairing any other masonry deficiencies as these defects can provide paths for moisture infiltration. It is important to perform repairs regularly as deteriorated masonry is susceptible to cyclic freeze-thaw, which can then further accelerate deterioration of the wall. One must select a suitable mortar type for the wall for rebuilding or repointing. Often mortar in older buildings is softer than modern-day mortar. In brick masonry the mortar is typically considered the “sacrificial” part of the wall system, meaning it is eventually expected to fail and to require repointing while the brick masonry units remain. However, if too strong of a mortar is selected for the given brick units, it can result in premature failure of the brick units themselves. A petrographic analysis can be performed on an existing mortar sample to provide more information about its makeup (cementitious materials vs. aggregate) and likely strength properties. ASTM C270 – Standard Specification for Mortar for Unit Masonry provides information to assist in specifying an appropriate mortar. The relative strengths of these mortar types can easily be remembered with “MaSoN wOrK,” where Type M is a high-strength mortar (28-day minimum compression strength of 2500 psi) that can be used in below-grade construction; Type S is a fairly high-strength mortar (28-day minimum compression strength of 1800 psi) with good flexural strength that can also be used in below-grade construction; Type N is a general purpose mortar (28-day minimum compression strength of 750 psi); Type O is a lower-strength mortar (28-day minimum compression strength of 350 psi) not suitable for environments susceptible to freezing; and Type K is a lower-strength mortar associated with historic masonry (though no longer included in ASTM C270).

The various brick masonry units available also have a range of properties. Clay masonry unit compressive strengths can range from 3,000 lbf/in2 to 20,000 lbf/in2. ASTM C216 – Standard Specification for Facing Brick (Solid Masonry Units Made from Clay or Shale) classifies brick masonry units as either Grade SW (3000 psi minimum compressive strength) for severe weathering resistance or MW (2500 psi minimum compressive strength) for moderate weathering resistance. The masonry is also classified as Type FBS or FBX depending on the precision desired for the unit size. FBS is used in general masonry while FBX is more precise. FBX units are also held to a higher standard for the maximum permissible chipped units in the wall.

Beyond choosing an appropriate brick unit and mortar, existing brick masonry walls may have been previously painted or coated with unknown materials adding another element to consider for masonry repairs. Masonry coatings can be clear or colored. A clear coating may go unnoticed, but often the texture of the wall can be indicative of a previous coating application. Colored coatings, as the name suggests, change the color of the brick and mortar, making their presence readily known. It is generally considered good practice to maintain a coating on the brick wall if it has been coated previously, but it can be difficult to select an appropriate coating during repairs if the original coating material is unidentified; not to mention, the wrong coating can do more harm than good. The water vapor transmission rate of the coating should be considered as this will impact the brick masonry’s ability to absorb and evaporate moisture from its face. If the masonry is unable to evaporate water from its face it becomes more susceptible to accelerated deterioration, including from cyclic freeze-thaw. The Brick Industry Association (BIA) provides technical information and guidance on when to apply a brick masonry coating in their Technical Note 6A from August 2008. And building enclosure consultants are available to help facility managers navigate through challenges and many other issues specific to a building’s brick masonry.