Chapter 4: Special Design Considerations

Table of Contents

Chapter 1: Introduction

Chapter 2: Masonry Systems

Chapter 3: The Building Enclosure

Chapter 5: Quality Control & Assurance

Chapter 7: Single-Wythe CMU Systems

Chapter 8: Thermal Performance & Energy Code Compliance

Appendix A:

Thermal Modeling

Glossary of Terms

Terms

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This chapter focuses on masonry wall design elements and construction considerations. Specific design elements include masonry flashings, movement joints, penetration detailing, and surface-applied and integral water repellents. Good design and sound construction practices will minimize the risk of water ingress, freeze-thaw decay, and efflorescence, resulting in the long-term durability and performance of masonry cladding.

Masonry Flashings

Flashing components are used in both rainscreen and mass wall systems to divert or deflect liquid water away from the masonry wall system, to provide a capillary break between masonry and other materials, and/or to protect less-robust underlying materials such as flexible membranes.

In masonry wall systems, flashings may be:

Formed from flexible membranes with or without an adhesive backing.
Formed from sheet metal.
Integral to masonry or precast concrete elements.
A combination of any of the above.

Common locations for masonry flashings are identified in Fig. 4-2.

Effective flashings are durable and waterproof materials that can be manipulated or formed to provide a continuous water-shedding surface or be integrated with the water-resistive barrier to provide water control and a continuous drainage plane.

Flexible membrane flashings are concealed by the masonry cladding or sheet-metal flashing elements and are typically found at floor line transitions, at parapet caps, within rough openings, and around wall penetrations. Where flexible flashing materials are used, it is important to consider the materials’ ability to withstand ultraviolet (UV) exposure. Materials sensitive to UV exposure are typically concealed with additional flashing materials such as sheet-metal drip plates or counterflashings for protection. Fire propagation concerns may also need to be addressed for some asphalt-backed flexible flashing materials; refer to the local building code for requirements.

Sheet-metal flashings may be either exposed or concealed within the assembly. Often, sheet-metal flashings—particularly stainless-steel—are thermally less conductive than other metal types. Stainless steel is relatively inert to the corrosiveness of mortar and provides a similar level of durability and longevity as the masonry veneer. Prefinished galvanized sheet-metal products may be used in masonry veneer applications; however, they may have a shorter service life and require replacement before the masonry veneer. The Architectural Sheet Metal Manual¹ published by the Sheet Metal and Air Conditioning Contractors’ National Association has additional discussion on the design and installation of sheet-metal components including for masonry systems.

Above and below wall penetrations (e.g., head, jamb, and sill flashings at windows, doors, and service penetrations).
At perpendicular wall interfaces (e.g., parapet-to-wall or roof-to-wall saddle flashings).
At parapet tops and roof or balcony edges (e.g., parapet copings and edge flashings).
At floor lines (e.g., cross-cavity sheet-metal flashing at anchored masonry veneer wall ledger locations).
At vertical support elements (e.g., base-of-wall flashings).

Cross-cavity flashings, such as those that occur at floor line transitions of anchored masonry veneer wall systems and through-wall flashing are commonly used interchangeably; however, there is a technical difference: a cross-cavity flashing is integrated with the WRB system and extends through the air cavity of an anchored masonry veneer while a through-wall flashing extends through the entire depth of the wall, such as one might see at the base of a single-wythe CMU wall system.

Flashing components that are integral to the masonry include sloped masonry elements—such as a sloped precast concrete window sill or cornice projecting beyond the cladding plane—and form a drip to encourage water shed.

Consider the following design characteristics to improve the ability of the flashing to enhance the long-term performance of the building’s façade:

Slope. Slope flashings to drain away from the building or material transitions.
Drip edges. Form drip edges to shed water away from the building face. Drip edges may include hemmed sheet-metal edges or drip kerfs in the underside of precast concrete components.
Continuity. Require continuous flashing materials. Specify minimum lap dimensions as recommended by the flexible membrane manufacturer or industry-standard resources for sheet metal. Continuity can be achieved by fully adhering or sealing the laps of flexible membranes or sheet-metal flashings. Typically, sheet-metal flashings are sealed with high-quality silicone or butyl-based sealant, or they may be soldered. Continuity of precast concrete components typically includes an elastomeric sealant joint with an appropriate backer material.
End dams. Provide end dams where flashing materials terminate, such as at the jambs of fenestration products to divert water away from the veneer wall air cavity or penetrations within the masonry wall system. End dams are typically shop- or field-formed from flexible and sheetmetal flashing products and are an integral element of precast concrete components such as window sills. 9 Back dams. Provide back dams on flashing materials. This may include vertical back legs on flexible or sheet-metal flashing components (typically 4 inches or greater) or stepped profiles on precast concrete elements.

Movement accommodation. Position flashing components such that anticipated building movement will not disrupt the flashing’s long-term performance. Fig. 4-3 describes an example of building movement adversely affecting the sheet-metal flashing profile and function.
Integration into the water-resistive barrier. Shingle-lap flashing components into the water-resistive barrier where the flashing is intended to drain the water control layer of a rainscreen wall system (e.g., anchored masonry veneer systems).
Counterflashing. Counterflash wall components with a flashing material (typically an adhered flexible flashing membrane concealed by a sheet-metal flashing) to provide a continuous water-shedding surface such as at a parapet cap.
Thermal performance. Stainless steel has a lower thermal conductivity than galvanized steel; thus, sheet-metal flashings formed of stainless steel are expected to contribute to less heat loss where the flashing bridges insulation layers. Self-adhered sheet flashings create even less of a thermal bridge where bridging insulation layers.

This guide recommends clearly depicting the above characteristics throughout construction drawings and describing them in project specifications.

Movement in Masonry Systems

Over time, volumetric changes will occur within any above-grade wall system and can result from temperature changes, moisture, elastic deformation, settlement, and creep. The amount of movement that occurs will depend on the building materials used within the wall system and on the intensity of the influencing mechanism (e.g., temperature change). In general, wood frame members, CMU, and stone will shrink, whereas clay masonry will expand. If steel stud framing or a CMU backup wall are used and are properly protected, minimal volume change is expected, except where specifically designed for.

Different materials within each wall system may move differently in relation to one another. If not properly designed for, differential movement can cause unwanted cracking, spalling, buckling, settlement, or separation within the building structure or veneer. Differential movement can also cause damage to other enclosure components such as the water-shedding surface, as demonstrated by the example in Fig. 4-3.

In this guide, the discussion and design of movement joints is considered in relation to differential movement between the veneer and wall structure, including control and expansion joints within the masonry veneer. A discussion of where to locate and how to size building-specific expansion joints that occur within the wall structure is beyond the scope of this guide and must be appropriately designed for and integrated into the abovegrade wall system where they occur. The discussion provided for locating movement joints within the masonry system is for general reference only; the Designer of Record is responsible for appropriately designing for all building movement.

Locating Movement Joints

General rules for locating movement (i.e., expansion or control) joints as they relate to the wall systems in this guide are:

For anchored clay masonry veneer, provide expansion joints such that long wall sections do not exceed 25 feet at occupied space and 15 feet at parapet conditions. At wall sections that have openings, joint locations may be reduced to 20 feet apart. Additional guidance on brick veneer expansion joints may be referenced from BIA Technical Notes 18² and 18A.³
For anchored concrete masonry veneer, provide control joints such that long wall sections do not exceed a length-to-height ratio of 1 1⁄2. The maximum wall length between control joints is 20 feet. Additional guidance on concrete masonry veneer control joints may be referenced from NCMA Tek 10-4 Crack Control for Concrete Brick and Other Concrete Masonry Veneers. ⁴
For CMU wall structures, provide control joints such that long wall sections do not exceed a length-to-height ratio of 1 1⁄2. The maximum wall length between control joints is 25 feet. Additional guidance on control joints may be referenced from the NCMA Tek 10-2C Control Joints for Concrete Masonry Walls – Empirical Method. ⁵

There is no single set of recommendations for the placement and design of movement joints that will work for all projects. In some cases, joints may be added more frequently than needed for aesthetic purposes. In general, the following locations for movement joints are recommended within a masonry veneer or structure in addition to the above. Fig. 4-4 demonstrates an example of these locations.

Joint Placement – Vertical

Throughout long walls with no openings, as described in the previous section
At wall offsets and setbacks
Within 10 feet of corners
Around openings such as windows and doors
At intersections and junctions (at intersections of walls that serve different functions or are different heights/thicknesses or cladding types)
At parapets, aligned with joint placement at the wall area below
Where framing methods or materials change (e.g., where a concrete backup wall meets a framed backup wall)

Joint Placement – Horizontal

At floor lines, typically aligned with the top-of-wall and floor interface.
Below structural support elements such as shelf angles
Between cladding material changes

Horizontal joints are also recommended at various locations on a veneer wall system to allow for cavity drainage and building movement. This includes accommodating movement around penetrations affixed to or penetrating through the backup wall, in addition to the veneer.

The location of joints, to accommodate movement, drainage, and/or veneer air cavity ventilation, is further discussed and identified within Chapter 6 for anchored masonry veneer and Chapter 7 for single-wythe CMU; chapter details identify these locations with an asterisk (*).

Joint Design

Joints that accommodate movement in anchored masonry veneer and single-wythe CMU wall systems typically include a backer rod and sealant joint. Movement joints are typically designed and constructed to accommodate 3 to 4 times the anticipated movement and are no narrower than 3⁄8 of an inch. Movement joints should allow for unobstructed movement and also be free of debris, reinforcing, or other elements that may inhibit movement over the life of the building.

Joint sealants are a critical component of a movement joint and allow the joint to open and close mostly uninhibited while providing a continuous water-shedding surface. Sealant products ideal for use at masonry movement joints have these properties:

Movement Capabilities: The sealant selected should allow for expansion or compression of the sealant joint without permanent deformation. The recommended sealant product is classified as a Class 100/50 sealant per ASTM C920.⁶ This sealant has joint movement capabilities of a minimum 100% extension and 50% compression when tested to ASTM C719.⁷
Adhesion to Substrate: The sealant selected should demonstrate adhesion to porous substrates such as masonry and concrete. Where differing substrates occur at either side of the movement joint (e.g., at metal panel-to-masonry veneer interfaces), the sealant should have acceptable adhesion to both substrates. Sealant adhesion testing prior to and during field installation is highly recommended and should result in cohesive failure (rather than adhesive failure).
Durability: Movement joints at cladding should be UV-stable as well as durable when exposed to moisture and temperature fluctuations.

Longevity: The longevity of the sealant joint should be as great as possible to match the durability of the masonry. Masonry is a long-lasting cladding option and will likely outlive the sealant joint; however, to reduce the replacement frequency of the joint, this guide recommends a quality silicone sealant. When properly installed and maintained as needed, neutral cure silicone sealants can exhibit 20+ years of acceptable performance. Other sealant options such as hybrid or polyurethane sealants may perform acceptably for 10+ years before replacement is required.

Substrate (masonry or other)
Clean substrate per sealant manufacturer’s instructions, primed as needed for adhesion
Foam backer rod with bond breaker jacket, oversize rod 25% larger than width of joint to achieve hourglass profile after tooling.
Tooled sealant, sand joint surface where desired

Best Practices

These joint design best practices will promote long-term performance of a movement joint:

Select a quality sealant based on the criteria described in the Joint Design section of this guide.
Follow industry-standard best practices for sealant joint installation. This includes joint design and substrate cleaning and priming. As a useful resource, refer to the Dow Corning Americas Technical Manual⁸ as well as the joint dimensioning described in Fig. 4-5.

Architectural Considerations

Where there is a desire to minimize the visual appearance of movement joints, consider the following:

Select a sealant color similar to the mortar color.
Choose a sanded joint (a joint that has mason’s sand bed into the sealant following tooling) such as that shown in Fig. 4-6.
Consider details that minimize the visible area of the joint while still accommodating movement, such as the anchored masonry veneer floor line detail alternatives in Chapter 6 on page 63.
Include a provision in the project specifications for field mock-ups of typical horizontal and vertical movement joints. Review the mock-ups for joint installation quality, adhesion, and appearance.
Hide movement joints at inside building corners.

Cleaners, Repellents, and Coatings

In Colorado and southern Wyoming, surface-applied clear water repellents are not commonly applied to the masonry veneer wall systems in Chapter 6 of this guide. Surface-applied clear water repellents are commonly applied to the single-wythe CMU wall systems in Chapter 7 or an elastomeric coating may be used in targeted applications. An alternative to using surface treatments for CMU wall systems is integral water repellents, which are incorporated into the masonry block prior to construction and added to the mortar mix at the construction site. The success of a clear water repellent, integral water repellent, or elastomeric coating is reliant on appropriate product selection, cleaning procedures, and application methods. Although these products have several functions, as described below, their use does not compensate for poor masonry workmanship or detailing. This section covers cleaning methods and best practices for selection and application of clear water repellents, integral water repellents, and elastomeric coatings.

Cleaning Methods

Cleaning mortar or grout smears, construction dirt, staining, contaminants, and efflorescence from the wall during the construction phase is required prior to applying clear water-repellent coatings. When masonry surfaces will have an opaque coating, cleaning is only necessary to provide adequate adhesion between the coating and the masonry.

Several cleaning methods are available including hand, water, chemical, and abrasive. Cleaning procedures are selected based on masonry unit and mortar colors, texture, and the type of existing debris or contaminants. In general, select the least-aggressive cleaning method necessary to remove debris and contaminates and to effectively clean the wall. Over-cleaning masonry products or using excessive abrasion can alter the appearance of the masonry veneer or CMU and can lead to premature weathering. Using a lower-strength mortar type, where acceptable for structural considerations, can also minimize the intensity of cleaning required; for example, using a Type S mortar when a Type N mortar is sufficient for the project application may require additional cleaning effort.

For all cleaning methods, test-clean an inconspicuous area of the wall to confirm the effectiveness and acceptability of the cleaning method. Only water-clean when surface and ambient temperatures exceed 40˚F; applications of cleaning products that rely on a chemical reaction to be effective may require even warmer temperatures.

ASTM D57039 and BIA Technical Note 20¹⁰ are helpful resources for determining appropriate cleaning procedures for clay masonry units, whereas NCMA TEK 8-4A¹¹ provides helpful discussion on cleaning CMU block of various types and finishes. Also consult the masonry unit manufacturer and cleaning product manufacturer guidance documents (where applicable) prior to cleaning.

Surface-Applied Water Repellents

Surface-applied clear water repellents may be considered for unglazed anchored veneer or for exterior-exposed single-wythe CMU systems. Application of a clear water repellent can reduce water absorption of the veneer and CMU, as demonstrated in Fig. 4-7, while preserving or enhancing natural appearance and minimizing the need for cleaning frequency. By reducing how much water the masonry cladding absorbs, less frequent wetting-drying and freeze-thaw cycles are expected to occur, reducing the likelihood of premature weathering and water-related damage and staining.

There are two primary types of repellents: penetrating or film-forming.

Penetrating repellents penetrate the pores of the masonry while still allowing water vapor to diffuse through the masonry veneer. Common penetrating repellents include silicone resins, silanes, and siloxanes.
Film-forming repellents, such as acrylics, stearates, and urethanes, form a thin film on the surface of the masonry face and across smaller pores. As a result, film-forming repellents can reduce the drying ability of the masonry cladding.

Of the two repellent types, penetrating repellents—specifically silane/siloxane blend clear water repellents—are common; silanes penetrate deep into the pores of clay masonry, while siloxanes are deposited closer to the masonry surface. Both silanes and siloxanes chemically bond to clay masonry, CMU, and mortar in the presence of moisture and alkalinity; as a result, silane/siloxane-based repellents can provide 5 or more years of protection, making such blends a durable and relatively longer-lasting water repellent option.

Clear water repellent application to glazed masonry veneers is not recommended. Glazed surfaces reduce the penetrating ability of clear water repellent products, limiting the effectiveness of the application. When selecting a clear water repellent, the following characteristics/properties are desirable for long-term performance:

When selecting a clear water repellent, the following characteristics/properties are desirable for long-term performance:

Suitability for Substrate/Finish: Products selected are suitable for vertical above-grade wall applications and project-specific masonry cladding types. Manufacturer-published literature should indicate that the product is acceptable for the type of masonry substrate and finish (e.g., split-faced CMU, fired clay brick, etc.).
High Vapor Permeance: Water repellence test results indicate approximately 90% or more of the untreated masonry product vapor permeance is retained when tested to ASTM E96.¹² Effective Water Penetration Resistance: ASTM E514¹³ results indicate a minimum 85% reduction in maximum leakage rate when compared to an untreated wall.
Block and Mortar Water-Repellent Admixture Compatibility: Where a clear water repellent is applied over CMU and mortar containing a water-repellent admixture, use a clear water repellent that is compatible with the admixture. Incompatible repellents may be less durable.

Where antigraffiti repellent properties are desired, consider using a vapor-permeable silicone-based or fluorosiloxane-based water repellent with penetrating properties that is also marketed as an antigraffiti repellent. The antigraffiti repellent should provide similar water penetration resistance and vapor permeance to the characteristics/properties listed above. The effectiveness of antigraffiti properties is demonstrated through ASTM D7089¹⁴ results, which may be used to compare the ease of graffiti removal.

Clear water repellents do not function as a water-resistive barrier or air barrier within a masonry system. Water repellents are also not effective at bridging cracks or filling voids that result from poor joint design/installation or from long-term building movement. Although clear water repellents will increase the masonry’s ability to shed water, a repellent will not prevent efflorescence resulting from water intrusion behind a masonry veneer and will require reapplication to be effective over the long-term service life of the building.

Best Practices

These general procedures and considerations are best practice for clear water repellent application:

Complete the cladding sealant joints (e.g., around window and door perimeters and at expansion/control joints) prior to application. Sealant joints should be fully cured (typically 14 to 21 days) prior to cleaning and application.
Clean masonry substrates to remove debris and surface contaminants prior to water repellent application.
Protect areas not to receive water repellent.
Prevent contact between clear water repellents and non-masonry products such as asphalt-based products, glazing and glass products, and landscaping.
Avoid applying sealant when rain threatens, when windy, and when minimum water repellent application temperatures are not met.
Perform a mock-up to demonstrate protection, cleaning, and water repellent application procedures and to review final masonry appearance.
Plan application extents to determine start and stop application locations; avoid overlap.
Apply water repellent in accordance with the repellent manufacturer’s installation instructions, including the application rate. General application requirements may include:

Beginning water repellent application on a dry substrate at lower surfaces, working upward as shown in Fig. 4-8. Fully saturate brushes and rollers, and provide a continuous stream for spray application. Brush away drips and runs
Where wet-on-wet application is required by the manufacturer, allow individual coats to penetrate for a minimum of 5 to15 minutes prior to reapplication.
Schedule reapplication of clear water repellent as prescribed by the manufacturer. Perform reapplication with the same or similarly formulated clear water repellent.

Integral Water Repellents

Integral water repellents are primarily used for weather-exposed single-wythe CMU systems and are incorporated in both CMU block and mortar. Repellents reduce the absorption and liquid water storage capacity of the masonry block and mortar and thus reduce the risk of efflorescence or staining. However, this reduced storage capacity requires even more care to ensure a continuous water-shedding surface at the block wall face, transitions, and penetrations.

Integral water repellents alone do not singularly manage the water penetration resistance performance of a CMU wall system and have little impact on resisting water ingress at cracks or voids within the field of the wall. For these reasons, the integration of water-shedding measures such as flashing systems, weeps, vents, and control joints are critical to prevent moisture penetration in block walls. Proper design and quality workmanship are also critical to achieve a watertight system. This guide recommends that mortar joints be tooled with a concave or V-shaped profile to mitigate the risk of poor compaction and bond strength, especially when using integral water repellents in the mortar mix. Other joint profiles, such as raked, extruded, beaded, struck, or flush can create ledges to hold water and are not recommended.¹⁵

Integral water repellents can improve the long-term color retention of colored block, such as that commonly used for split-face block applications. Integral water repellents do not alter the finished appearance of the masonry walls (i.e., texture or color) and are a permanent part of the system; therefore, they do not require reapplication after a certain period to maintain the system’s water repellency. Surface-applied products may be used with integral water repellents for added water penetration resistance at the surface; however, they will require reapplication for long-term performance. ¹⁶

For CMU block, the water-repellent admixture is added into the concrete mix during the manufacturing process of the concrete masonry units and becomes evenly distributed throughout each block. For mortar, a compatible admixture product is incorporated into the mortar as it is mixed on-site. Integral water-repellent admixtures for preblended mortar products are typically powders added to the mortar mix during the manufacturing process. ¹⁷ Site-mixed water repellents are typically liquid admixtures.

It is critical that all CMU block and mortar, including other masonry components such as precast sills and lintels, contain the same or compatible integral water-repellent products and that those water-repellent products are compatible with other admixtures. The bond strength between mortar and CMU units may be compromised if incompatible products are used. ¹⁵ An adequate bond allows for continuity of the water control layer and water-shedding surface, especially at joint interfaces.

Clean CMU wall systems that include integral water repellents in accordance with the manufacturer’s instructions. Avoid high-pressure water cleaning; it can reduce the effectiveness of the integral water repellent.¹⁸

Best Practices

These general application procedures and considerations are best practices for integral water repellent selection and application:

Confirm the compatibility of the integral water repellent used both in the CMU blocks and in the mortar with the wall system grout or surface-applied repellents and coatings.
If site-mixed integral water repellents are selected, incorporate the proper dosage of water-repellent admixture. Incorrect dosage can influence the workability of the mortar for masons and the performance of the repellent.
Avoid the installation of integral water-repellent block and mortar in locations where the wall may be immersed in water over time, i.e., in below-grade applications.
Specify concave or V-shaped mortar joint profiles to encourage water to run off the wall face.
Clean the masonry wall in accordance with the integral water repellent manufacturer’s instructions.

Elastomeric Coatings

Elastomeric coatings reduce the amount of water absorbed by masonry substrates and provide crack-bridging properties that help reduce water leaks. Elastomeric coatings are typically installed where additional water penetration resistance is desired and where a painted surface is visually acceptable. Elastomeric coatings are most commonly used on CMU wall systems. An example of an elastomeric-coated CMU wall is shown in Fig. 4-9. Elastomeric coatings may serve as a water-shedding surface, water-resistive barrier, and air barrier on the exterior face of a masonry substrate when a UV-stable coating is used and installed at the required thickness. It should be noted, however, that elastomeric coatings sacrifice the visible benefits of the masonry surface and can be prone to discoloration, abrasion, and other damages.

This guide recommends a vapor-permeable silicone or acrylic elastomeric coating with UV resistance and high elongation properties to achieve a good coating. A vapor-permeable coating allows the masonry substrate to dry and reduces the likelihood of salt buildup and bubbling or blistering of the coating.

When selecting an elastomeric coating, these characteristics/ properties are desirable for long-term performance:

Product Suitability: Products suited for vertical abovegrade wall applications with UV resistance.
Water Penetration Resistance: No leaks at the field of wall area when tested to ASTM D6904.¹⁹
Vapor Permeance: A minimum vapor permeance of 8 perms when measured per ASTM E9612 wet cup method at the manufacturer-recommended dry film thickness.
High Elongation Properties: Elongation properties that exceed 300% when tested per ASTM D412.²⁰
Crack-Bridging Ability: No cracking when tested to ASTM C1305.²¹
Validation: Products that include an “SWR Institute Validation Program” label on the product data sheet.²² This label validates performance properties and can be helpful for comparing product options with the program label.

Elastomeric coatings can exhibit staining and may be difficult to clean. Surface staining is largely attributed to surface wetting from runoff below horizontal or sloped surfaces and penetrations including flashings, windows, and parapets. Staining can largely be reduced by reducing the amount of water that runs onto the wall from these dirt-collecting surfaces. This guide recommends using sheet-metal drip edges (such as at window and door sills) to deflect water away from the surface of the masonry coating to help reduce staining

Best Practices

These general application procedures and considerations are best practices for elastomeric coating application:

Include consideration for water shedding and deflection in above-grade wall design. Use minimum 1⁄2-inch projected drip edges to minimize coating staining and runoff.
Provide a minimum 28-day cure for masonry mortars and adjacent concrete surfaces prior to application.
Seal all cracks and cladding joints as recommended by the coating manufacturer, with the exception of intentional drainage gaps and weeps. Use appropriate joint design and backing at movement joints. Typically, cracks or holes 1⁄16-inch wide or greater require treatment.
Use block filler on CMU walls when required by the manufacturer. Some manufacturers may allow an additional application of coating in lieu of block filler.
Test the coating adhesion to confirm cleaning procedures and priming requirements to the masonry substrate and joint sealants. Use a mock-up for coating review prior to full-scale application.

Long-Term Cladding Performance

The long-term durability and performance (including aesthetic performance) of masonry cladding starts with good design, is implemented with sound construction practices, and is preserved with regular maintenance over the service life of the building.

This section addresses how good design can extend the masonry cladding service life and minimize the risk of efflorescence and the risk posed by freeze-thaw cycles in masonry cladding.

Extending Cladding Service Life

The following can help achieve average or greater service life of the masonry systems discussed in this guide:

Develop a building form with features that provide a continuous water-shedding surface and promote deflection of water away from the building, particularly at details and interfaces (see page 18). Ensure that water-shedding elements are constructed as continuous in the field.
Design and construct continuous water and air control layers (see page 21). Use a moisture-tolerant and durable water-resistive barrier system, air barrier system, and insulation materials within the drained and vented (where applicable) air space behind the cladding.
During design, select cladding attachment materials such as ties, girts, and fasteners and metal components such as sheet-metal trim and counterflashing elements whose service lives are similar to that of the cladding material. For example, stainless-steel components parallel the expected longevity of masonry wall systems. See Chapters 6 and 7 for discussion on Corrosion Resistance.
Specify masonry units appropriate for the project application and location of installation. See Chapters 6 and 7 for discussion on unit selection.
Implement a comprehensive maintenance program specific to the building. The following outline recommends frequencies for maintenance events:
- Immediately: Correct water diversion mechanisms that may have disconnected or failed, such as scuppers, gutters, or downspouts. –
- As needed: Repair localized cladding and cladding component damage or failure.
- Every 2 to 5 years: Review cladding for signs of distress or wear such as cracks/spalling, efflorescence, organic growth, or sealant joint failures, and repair or clean as needed. Repair moisture sources that may be causing or contributing to efflorescence.
- Every 5 to 10 years: Review the condition of mortar in masonry veneer walls. Repoint mortar as necessary.
- Every 5 to 10 years: Perform a comprehensive condition assessment of cladding and cladding components including sheet-metal flashing and copings, sealant joints, weeps, etc.
- Every 5 to 20 years: Reapply masonry sealers based upon intervals recommended by the sealer manufacturer.

Freeze-Thaw Cycles

Freeze-thaw cycles can be described as repeated freezing and thawing of moisture within masonry pores due to temperature fluctuations. Masonry decays with freeze-thaw cycles only if the moisture conditions are above a material-specific critical level. Reducing the moisture source, encouraging drying, or avoiding freezing temperatures can reduce the risk of freeze-thaw damage. An example of decay resulting from freeze-thaw cycles is shown in Fig. 4-10. The factors affecting both the occurrence of freeze-thaw cycles and the likelihood of resulting damage include climate, material properties, and building-specific design features and are described in the following sections.

Climate

Wet climates prone to rapid temperature swings and freezing temperatures have a greater risk of freeze-thaw occurrence. Freeze-thaw decay can occur anywhere in Colorado and southern Wyoming; however, it is more likely to occur in areas that experience colder freezing temperatures and greater precipitation, including snowfall and building areas subjected to splashback.

Climate is a factor beyond the control of the designer and mason contractor; thus, building materials and building-specific design are of greater focus for minimizing freeze-thaw damage in higher-risk areas of Colorado and southern Wyoming.

Material Properties

Porosity, pore structure/size, material strength, and saturation coefficient of the masonry material all affect the occurrence of and subsequent damage due to freeze-thaw cycles. While the direct relationships between these material properties and freeze-thaw occurrence are not described here, each chapter provides recommendations for specifying masonry components that are appropriate for exterior application and that limit the risk of freeze-thaw damage.

Most freeze-thaw damage seen on new buildings is seen on clay brick and natural stone façades. ASTM standards are available for various natural stone products, which require similar repeated freeze-thaw testing at moisture contents close the material’s saturation level during extended rain exposure events. These standards may be conservative for some applications where the façade has limited rain exposure.

In most new building projects, manufactured clay brick must meet criteria established by ASTM International in the United States. ASTM Standard C62²³ and ASTM Standard C216²⁴ grade brick based on its resistance to frost damage as severe weathering (SW), moderate weathering (MW), or negligible weathering (NW). Clay bricks in Colorado construction are required to be of the severe weathering grade.

The ASTM specifications prescribe only that a brick needs to either meet the maximum saturation coefficient or the cold water absorption criterion; it need not meet both. Alternatively, similar testing as that for natural stones can be performed to show compliance.

Note that the procedures used for clay brick in calculating the values of acceptance criteria are contained in a separate standard: ASTM Standard C67.²⁵ The acceptance criteria used by ASTM were selected under the assumption that adequate open-pore space should be provided to accommodate expansion of water as it freezes;²⁶ however, a significant fraction of bricks that pass the ASTM criteria subsequently fail in service, while other bricks that fail the standard have been proven durable in practice.²⁷ Hence, new clay bricks should be expected to have some vulnerability to freeze-thaw decay. Furthermore, Appendix X4 of ASTM C216-07a includes the disclaimer that “in severe exposures, even Grade SW brick may spall under certain conditions of moisture infiltration, chemical actions, or salt crystallization.”²⁴ For building designers using clay brick, the moisture management approaches provided in this guide will help the façades avoid saturation above critical levels for most building applications. Cold climate façades with direct exposure to lake or sea spray or severe driving rain should consider criteria beyond these ASTM standards to ensure the durability of clay brick products for those specific applications.

Building-Specific Design

Building-specific design concepts of masonry systems are within the control of the designer and can greatly reduce freeze-thaw occurrence and related damage. These building-specific design concepts are important to consider, especially within higher-risk areas of Colorado and southern Wyoming:

Building-specific form and features that reduce the cladding exposure to liquid water and snow accumulation. See Chapter 3 for more discussion.
Site design that locates water sources such as irrigation and outdoor water features away from the building enclosure.
Drainage behind the masonry veneer (such as that shown in the systems in Chapter 6), which minimizes water buildup behind the masonry cladding; venting/ventilating behind the veneer, which encourages drying to remove moisture within the veneer.
Appropriate selection of air barrier materials and design of air barrier transition details as discussed throughout all chapters of this guide. Excessive pressurization of humidified buildings should also be avoided. Excessive air leakage condensation on masonry materials can increase the moisture within the masonry and thus also increase the freeze-thaw risk.

Note that many of the building-specific design concepts beneficial for ensuring the long-term durability of the masonry wall or veneer are also beneficial for the long-term performance of the system as a whole. The above concepts also reduce the likelihood of water leaks and heat loss/energy consumption and can improve the long-term durability of the structure and masonry cladding.

Efflorescence

Efflorescence, as shown in Fig. 4-11, occurs when water-soluble alkali salts within the masonry unit, mortar, and/or grout are dissolved by water and migrate to the surface of the masonry wall or veneer. Water evaporates when it reaches the exposed surface of the masonry, leaving the salts behind—which typically appear as a white residue. Minimizing wetting of the cladding through good design as discussed throughout this guide, sound construction practices, and regular long-term maintenance can help prevent efflorescence.

It is typical for some efflorescence to form on masonry veneer and walls systems immediately following installation due to moisture within the grout and mortar materials during construction. Should efflorescence be observed following the final cleaning of the masonry veneer after installation, a source of moisture may be present and should be investigated and repaired as needed.

Chapter Reference

Sheet Metal and Air Conditioning Contractors’ National Association, Inc. Architectural Sheet Metal Manual, 7th ed. (Chantily, VA: SMACNA, 2012).
The Brick Industry Association. Technical Note 18 Volume Changes – Analysis and Effects of Movement (Reston, VA: The Brick Industry Association, 2006).
The Brick Industry Association. Technical Note 18A Accommodating Expansion of Brickwork (Reston, VA: The Brick Industry Association, 2008).
National Concrete Masonry Association. TEK 10-4 Crack Control for Concrete Brick and Other Concrete Masonry Veneers (Herndon, VA: National Concrete Masonry Association, 2001).
National Concrete Masonry Association. TEK 10-2C Control Joints for Concrete Masonry Walls – Empirical Method (Herndon, VA: National Concrete Masonry Association, 2010).
ASTM International. ASTM C920-14a Standard Specification for Elastomeric Joint Sealants (West Conshohocken, PA: ASTM International, 2014).
ASTM International. ASTM C719-14 Standard Test Method for Adhesion and Cohesion of Elastomeric Joint Sealants Under Cyclic Movement (Hockman Cycle) (West Conshohocken, PA: ASTM International, 2014).
Dow Corning. Dow Corning Americas Technical Manual (n.p.: The Dow Chemical Company, 2002-2017).
ASTM International. ASTM D5703-95(2013) Standard Practice for Preparatory Surface Cleaning for Clay Brick Masonry (West Conshohocken, PA: ASTM International, 2013).
The Brick Industry Association. Technical Note 20 Cleaning Brickwork (Reston, VA: The Brick Industry Association, 2006).
National Concrete Masonry Association. TEK 8-4A Cleaning Concrete Masonry (Herndon, VA: National Concrete Masonry Association, 2005).
ASTM International. ASTM E96/E96M-16 Standard Test Methods for Water Vapor Transmission of Materials (West Conshohocken, PA: ASTM International, 2016).
ASTM International. ASTM E514/E514M-14a Standard Test Method for Water Penetration and Leakage Through Masonry (West Conshohocken, PA: ASTM International, 2014).
ASTM International. ASTM D7089-06(2014) Standard Practice for Determination of the Effectiveness of AntiGraffiti Coating for Use on Concrete, Masonry and Natural Stone Surfaces by Pressure Washing (West Conshohocken, PA: ASTM International, 2014).
National Concrete Masonry Association. TEK 19-1 Water Repellents for Concrete Masonry Walls (Herndon, VA: National Concrete Masonry Association, 2006).
National Concrete Masonry Association. TEK 19-7 Characteristics of Concrete Masonry Units with Integral Water Repellent (Herndon, VA: National Concrete Masonry Association, 2008).

National Concrete Masonry Association. TEK 19-2A Design for Dry Single-Wythe Concrete Masonry Walls (Herndon, VA: National Concrete Masonry Association, 2004).
Northwest Concrete Masonry Association. Tek Note Rain-Resistant Architectural Concrete Masonry (Mill Creek, WA: Northwest Concrete Masonry Association, 2014).
ASTM International. ASTM D6904-03(2013) Standard Practice for Resistance to Wind-Driven Rain for Exterior Coatings Applied on Masonry (West Conshohocken, PA: ASTM International, 2013).
ASTM International. ASTM D412-16 Standard Test Methods for Vulcanized Rubber and Thermoplastic Elastomers— Tension. (West Conshohocken, PA: ASTM International, 2016).
ASTM International. ASTM C1305 Standard Test Method for Crack Bridging Ability of Liquid Applied Waterproofing Membrane (West Conshohocken, PA: ASTM International, 2016).
Sealant, Waterproofing & Restoration Institute. “SWR Institute Validation Program.” SWR Institute. Accessed January 1, 2018. www.swrionline.org/Validation.
ASTM International. ASTM Standard C62-17, Standard Specification for Building Brick (Solid Masonry Units Made From Clay or Shale). (West Conshohocken, PA: ASTM International, 2017).
ASTM International. ASTM Standard C216-07a, Standard Specification for Facing Brick (Solid Masonry Units Made from Clay or Shale). (West Conshohocken, PA: ASTM International, 2017).
ASTM International. ASTM Standard C67/C67M-18 Standard Test Methods for Sampling and Testing Brick and Structural Clay Tile (West Conshohocken, PA: ASTM International, 2018).
Crawford, C.B. 1984. “Frost durability of clay bricks— Evaluation criteria and quality control.” Proceedings of the CBAC/DBR Manufacturers’ Symposium, 1984. Ottawa, ON: NRCC.
John Straube, Christopher Schumacher, and Peter Mensinga. 2010. “Assessing the freeze-thaw resistance of clay brick for interior insulation retrofit projects.” In Proceedings of the Thermal Performance of the Exterior Envelopes of Whole Buildings XI Conference, Clearwater, FL, December 5-9, 2010, 1-8. Clearwater, FL: American Society of Heating, Refrigerating and Air-Conditioning Engineers.