Building with Brick and Masonry

August 11, 2010

Building with Brick and Masonry (Continued from p. 52 of the August 2008 issue of BD+C)

Mortars and Mortar Joints. Mortar is yet another factor greatly influencing the aesthetics of brickwork. Mortar comes in many different colors and textures. According to the BIA, mortar’s four basic roles are:

                    
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Reed Business Information is a Registered Provider with the American Institute of Architects Continuing Education Systems. Credit earned on completion of this program will be reported to CES Records for AIA members. Certificates of Completion for non-AIA members are available on request.
       This program is registered with the AIA/CES for continuing professional education. As such, it does not include content that may be deemed or construed to be an approval or endorsement by the AIA of any material of construction or any method or manner of handling, using, distributing, or dealing in any material or product. Questions related to specific materials, methods, and services will be addressed at the conclusion of this presentation. 
   

1. Bonding the brick units together and sealing the spaces between.
2. Compensating for minor dimensional variations in the units.
3. Bonding to steel anchors and ties, connecting the brick wythe to other wythes or structural backup.
4. Providing a decorative effect on the wall surface by creating shadow lines, colors, and textures.

Mortars may be successfully tinted to enhance the patterns in brick, although the pigments used for tinting must be fine enough to disperse evenly throughout the mix. The pigments and additives should also be compatible with the mortar mix—and they should be tested for color matching. The BIA and many masonry contractors recommend using cement and coloring agents premixed in large, controlled quantities. 

“Premixing large quantities will assure a more uniform color than can be obtained by mixing smaller batches at the job,” notes the BIA.

There are numerous kinds of mortar joints as well. Those that most effectively resist rain penetration include concave, V-shaped, and grapevine joints. Troweled joints include the weathered joint, which also resists water penetration well. For situations where water penetration is not a major concern, there are also beaded, struck, raked, and flush or roughcut joints.

Given all these choices and techniques, brick and mortar have proven to be the building blocks of creative design. Besides joint and mortar treatment, the key elements of brick expression include positioning, bond patterns, façade textures, accent pieces, bands, arches, corbelling, and recesses and projections.

Sustainability and Brick
Is brick green? Not surprisingly, this ancient material serves the environment almost as well as it serves Building Teams.
 

                   
    Clicks and Bricks
While the challenge is certainly not unique to brick construction, the team coordination required for brick structures raises questions about accuracy and completeness. First, there is the task of quantity estimating. Even if that is right, on a project with three types of brick, for example, someone may change a product or mortar type and tell the detailers and contractors, but forget to tell other team members.

Further, Building Teams can’t always automatically be sure which objects in a brick assembly are being counted in a cost estimate, as opposed to what’s described in specifications and drawings, contends Susan McClendon, executive vice president of Building Systems Design, Atlanta. The CAD environment provides information on the wall’s dimensions, while the specifications focus on its physical properties.

What’s the solution? McClendon describes the need for a standard taxonomy across various software applications to “premap” the data.

A similar solution is to make better use of CAD and building information modeling (BIM) tools, which can be especially helpful tools when designing with brick, says M. Teresa Hurd, AIA, LEED AP, a senior vice president with HKS, Dallas. “Three-dimensional CAD techniques can be very useful in figuring out the geometry of intersections and corners and depicting it accurately for the contractor to understand the design intent as well as how to build it,” she says.

Professionals like McClendon and Hurd recognize, however, that a lack of standardization and interoperability is currently inhibiting the potential for CAD and BIM to help automate the brick construction process.
                          

According to many life cycle analysis (LCA) calculations, the embodied energy of brick—that is, the energy required for raw material extraction, manufacturing, and transportation—is generally much lower than that for most other building materials, including concrete, glass, steel, and fiber-cement. In addition, brick structures can earn points toward the U.S. Green Building Council’s LEED rating system in a number of categories, including points for storm water management, energy performance, reuse and waste management, use of regional materials, and reduction of heat island effect.

“When it comes to pairing brick masonry with LEED, brick’s life cycle expectancy, local or regional manufacturing, and thermal mass make this construction medium a perfect fit for sustainable construction,” said the MCAA’s Jennie Farnsworth, editor of the group’s publication, Masonry. In terms of reuse and waste management, brick creates little waste in its manufacturing process: according to an expert in brick making, mining one pound of clay produces nearly one pound of brick, with only a slight loss of moisture and mineral content. Compare that to steel, which loses about 70% of the mass of the iron ore it consumes in manufacture, or aluminum, which demands about 88% loss of materials from the original bauxite ore.

As for energy efficiency, Patricia Hohmann, AIA, LEED AP, and principal with Hohmann & Barnard, Hauppauge, N.Y., adds that bricks “can also be used in passive solar construction by utilizing their heat capacity and thermal lag to reduce peak energy loads, thus decreasing the size of the building HVAC system.” Light-colored bricks and pavers can contribute to reducing energy needs and heat island effect. The use of permeable pavers also helps control stormwater runoff.

On the job site, brick brings other green advantages. For example, due to brick’s small, modular shape, on-site construction waste is minimal. Scrap brick can be used as fill, whole or crushed. “Brick and other masonry are among the most commonly salvaged building materials,” says Hohmann. Bricks also often contain recycled materials such as sawdust and manganese, while mortar can be manufactured with fly ash, a residue from the combustion of coal.

According to the BIA article “Brick for Sustainable and Green Building Design,” the following benefits of a single brick wythe contribute to sustainability and energy efficiency:
• Serving as a load-bearing structural element that also provides impact resistance from wind-borne debris or projectiles.
• Providing acoustic comfort with a sound transmission class (STC) rating of 45 or greater.
• Regulating indoor temperatures as a result of thermal mass, and serving as a heat-storing element in a passive solar design.
• Providing fire resistance, with a nominal four-inch brick wall offering a one-hour fire rating.
• Improving indoor air quality by eliminating the need for paint and coatings—as well as being inorganic and therefore not a food source for mold.

Moisture Control for Brick Enclosures
Although the humble brick’s aesthetics, environmental footprint, and functionality are impressive, one thing to keep in mind is the fact that brickwork will not stop water. Unless properly addressed, water penetration can be a serious issue. “Protecting the wall against water infiltration is probably the most important aspect of brick detailing. If water is not allowed to weep out of the wall, it can cause problems with freezing in the winter and mold growth in the summer,” cautions HOK’s Romano.

To call attention to this issue, Naperville, Ill.-based Packer Engineering recently tested a 12-square-foot brick façade against simulated wind-driven rain. In the end, the test revealed that a brick wall can leak as much as one gallon of water per hour. 
 

     
   
Upgrading to Brick Veneer
When it comes to renovating an existing wall with brick veneer, most exterior walls—including wood, steel, and masonry walls in commercial construction—are strong enough to serve as the backing for anchored brick veneer or to carry the weight of thin brick adhered veneer. The weight of anchored veneer can be carried by the foundation or the structural frame.

The brick veneer must be securely attached to the existing construction throughout its height to transfer wind load. The type of anchor system and fastener will depend on the construction of the existing wall that will become the backing. Properly detailed, the veneer shouldn’t affect the wall’s ability to resist wind pressures.

Just as important to the renovation is a water-resistive barrier. Even if an existing building façade is sufficiently strong to hold up the veneer, uncontrolled moisture intrusion will dramatically shorten the life of the new enclosure.

The benefits of cladding an existing wall go far beyond aesthetics, too: The new layer of brick veneer will serve as added thermal insulation, acoustical isolation, and even protection from wind-borne debris.
     

“The most important thing is remembering that brickwork is not weatherproof by itself,” emphasizes Hurd of HKS. “It requires a consistent barrier system behind it, including sheathing with either a vapor barrier or an air barrier depending on climate, and flashing with end dams at each termination. Also, openings, corners, and transitions to other materials require special attention to ensure that the consistency of the flashing system is maintained.”

Choices for flashing materials include plastic, copper, and stainless and galvanized steel—materials that are “impervious to water, tough enough to withstand construction abuse, and yet flexible enough to conform to the desired shape, and not deteriorate while in service. It should also not react with mortar or corrode and should be compatible with joint sealants,” according to a BIA technical white paper. 

Location of the flashing in critical areas prone to water intrusion is also crucial, says Richard Applebaum, P.E., SECB, president of Klepper Hahn & Hyatt, Syracuse, N.Y. “It is very common for water to leak through the head joints between coping sections and deteriorate the wall below.” he explains. “Consequently, you want to place flashing below the coping to protect the wall below.”

Joints, Sealants, and Barriers. Also pertinent to water management are drainage planes and weeps to direct water away from the building envelope, especially above all door and window penetrations, below window sills, and above the ground at the base of the wall. According to the BIA, in a drainage wall, water travels down the backside of the brick in the air space and is then channeled out with flashing sloped toward the face of the wall and through weeps spaced every few bricks at the mortar joints. Just as important, contractors need to be aware of mortar droppings behind the wall, which occur when bricks are pressed into place. The excess mortar can easily clog up weeps, rendering them ineffective. Consequently, experts recommend utilizing a mortar collection device to ensure that the droppings are kept out of the way.

Yet another key detail is the sealant joint, considered to be the primary defense against the ingress of air and water where doors and window penetrations interface with the masonry. “Sealant joints should be designed, detailed, and installed with the same care as other building components, not applied as an afterthought,” explains the BIA in its Technical Note 21B – Brick Masonry Cavity Walls – Detailing. “Too frequently, sealants are used to correct or hide poor workmanship, rather than being included as an integral part of the construction.”

Air barriers are also a critical component of many brick building envelope systems. Where brick walls are detailed with air barrier systems, the air barriers must be installed in a continuous manner with all penetrations and seams sealed, explains Kami Farahmandpour, P.E., founder and principal, Building Technology Consultants, Arlington Heights, Ill. “If an air barrier also is used as a weather-resistive barrier, all penetrations through it have to be sealed and properly flashed to resist water penetration,” he adds. “In addition, air barriers will have to be designed and installed to resist wind loads.” 

Farahmandpour explains that while it may be impractical to completely eliminate moisture condensation within wall assemblies, brick enclosure designs—like any other envelope type—should prevent moisture accumulation as much as possible. If any short-term exposure to moisture occurs, the wall design should ensure that the moisture effects will not impact wall components adversely.

Brick and Mortar Restoration
Although brick and mortar’s longevity and durability are among its outstanding attributes, it does need to occasionally be restored, particularly in historic structures. However, matching the existing materials may take considerable time and effort. “Making an addition blend seamlessly with existing walls can be challenging,” says Perkins+Will’s Turckes.

Robert C. Mack, FAIA, principal, MacDonald & Mack Architects, Minneapolis, and John P. Speweik, CSI, Toledo, principal, U.S. Heritage Group, Chicago, have studied historic renovations of brick structures on behalf of the National Park Service’s Department of Technical Preservation Services. In one of their reports, Mack and Speweik warned, “Even with the best efforts at matching the existing mortar color, texture, and materials, there will usually be a visible difference between the old and new work, partly because the new mortar has been matched to the unweathered portions of the historic mortar.”

In addition, Klepper Hahn & Hyatt’s Applebaum calls attention to the fact that today’s mortar is not often compatible with historic mortar as it is made of different ingredients. “Modern portland mortars are much stronger and less permeable than historic lime mortars,” he explains. “If you cap soft lime mortars with portland cement by repointing, you trap moisture within the lime mortar, which deteriorates through freeze-thaw action in winter climates, and by plant and mold growth in warmer climates.” To counter this, Applebaum recommends restoring solid masonry walls with mortar that is weaker and more permeable than the brick. This way a path is left for moisture to drain from the wall. 

That still leaves the challenge of matching mortar. Some Building Teams have used laboratory analysis, especially for important historical projects, to evaluate the ingredients of the original mortars employed. However, Mack and Speweik contend that the exact physical and chemical properties of the historic mortar are not critical as long as the new mortar conforms to the following criteria:
• The new mortar must match the historic mortar in color, texture, and tooling.
• The sand must match the original sand in the historic mortar.
Mack and Speweik emphasize that the color and texture of a new mortar will usually work well if the sand is matched successfully. However, Applebaum adds an important caveat:
• The new mortar must have greater vapor permeability and be softer than the masonry units.

Even where these conditions are met, it can be still be difficult to find an ideal matching formula for the original mortars. That may mean that spot repointing—the preferred approach for historic facilities operated by the National Park Service—may not be the best path if the color difference between old and new mortars is too extreme. In these cases, Mack and Speweik recommend repointing an entire area of a wall, or an entire feature such as a bay, to minimize the difference between the old and the new mortars.

Even though staining is one way to achieve a better color match, it’s generally not recommended. “Although staining may provide an initial match, the old and new mortars may weather at different rates, leading to visual differences after a few seasons. In addition, the mixtures used to stain the mortar may be harmful to the masonry; for example, they may introduce salts into the masonry which can lead to efflorescence,” according to Mack and Speweik. (Efflorescence is a chemical process resulting in salt being brought to the surface by water moving through the brickwork and evaporating, leaving behind a white deposit which adversely affects the masonry veneer.)

Caps and Coping
Another key design detail for brick structures is the detailing of copings—the covering at the top of the brick wall, often made of brick—and caps—protective units covering areas within the height of a wall, usually where there is a change in the wall thickness.

The primary function of caps and copings is to channel water away from the building, according to the BIA, which notes that the most critical consideration in the design of the coverings is the performance of the element in service. In other words, “The designer must take into consideration the movement of the element, differential movement between the element and the wall, joint configuration and material, connection of the element to the wall, and type and location of flashings,” according to the BIA’s Technical Note 36A on Brick Masonry Details, Caps and Copings, Corbels and Racking.

The cap or coping may be a single unit or multiple units, with the tops of the elements sloping in one or both directions. The units may also be made of several different materials, including pre-cast or cast-in-place concrete, stone, terra cotta, or metal—brick may match, but it is not preferred. According to the BIA, “brick is not well-suited to such extreme exposure, and brick caps and copings require more joints than do those made of other materials.”

As with any other building material, tradeoffs in aesthetic value and performance will affect the use of brick in building projects. Yet brick often brings a double benefit of beauty and functionality in a range of applications. Thanks to its many redeeming qualities such as sustainability, longevity, and design versatility, the simple and ancient method of stacking bricks and mortar will remain among the most prominent building blocks in the industry. As HKS designer Rupert Brown says, “The proven historical acceptance of brick reinforces it popularity as one of the most widely used materials today.”

As the MCAA puts it: “Masonry’s adaptability to design forms, richness in texture, its modern adaptation for structural requirements, minimum maintenance, and cost-competitiveness with other materials make it the preferred material for today’s buildings.”

About the authors
C.C. Sullivan is a communications consultant and author specializing in architecture and construction. Barbara Horwitz-Bennett is a writer and contributor to construction industry publications.

Take the AIA Exam  (one-time registration required)

This BD+C continuing education program qualifies for 1 AIA HSW learning unit.

Reed Business Information is a Registered Provider with the American Institute of Architects Continuing Education Systems. Credit earned on completion of this program will be reported to CES Records for AIA members. Certificates of Completion for non-AIA members are available on request.
       This program is registered with the AIA/CES for continuing professional education. As such, it does not include content that may be deemed or construed to be an approval or endorsement by the AIA of any material of construction or any method or manner of handling, using, distributing, or dealing in any material or product. Questions related to specific materials, methods, and services will be addressed at the conclusion of this presentation.

         
 

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