Choosing between restoring or replacing cracked, spalled, and displaced brick facades

by arslan_ahmed | January 27, 2023 10:00 am

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By Luke Niezelski, PE, and Stephen Holland PE

Restoring brick facades plays an essential role in reusing existing building stock. Every project should answer this question: can the facade be saved or has the brick’s deterioration critically compromised the wall’s stability? Existing brick masonry is often treated as a maintenance item and not much thought is given to whole system performance. Brick and mortar defects can be treated as symptoms, but the overall stability of the assembly is often overlooked.

Conversely, some designers may call for the full replacement
of an assembly, when salvaging and restoration is possible. This article examines damage caused by unrelieved differential movement in brick masonry walls and evaluates criteria for replacing versus restoring existing brick masonry.

Background

The existing brick building stock ranges from pre-20^th century historical landmarks to modern offices, schools, apartments, etc. These buildings have a range of brick construction styles and a range of perceived “value” when preservation is considered.  During the 20^th century, brick construction underwent a metamorphosis as tried-and-true brick mass walls merged with modern steel/concrete construction and a desire to create taller buildings. This metamorphosis divides brick walls into three broad categories.

Mass masonry

Mass masonry includes all exterior wall assemblies that developed air/water/thermal resistance by layering one or more wythes of masonry together. This can include a wide array of walls such as: three to four wythes of masonry, one solid piece of stone or concrete, one wythe of brick mortared onto a wythe of concrete masonry unit (CMU). The walls are intended to bear the weight of the structure, and this also limited building height to a maximum of seven to eight stories.

Transitional masonry

Transitional masonry design utilized steel/concrete frames as the building’s structure but continued to use mass walls as the building enclosure. This style was most commonly found in the 1920s-1950s.

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Cavity wall masonry

Cavity wall masonry includes an exterior wythe of brick/stone/other installed with an air gap, or cavity between the masonry veneer and the backup wall. The brick/stone is generally held in place with masonry ties, and water that infiltrates into the cavity can drain out of the assembly using through-wall flashings and weeps. This style became popular in the 1950s and is roughly the same style used in modern brick construction.

Buildings from all three categories still exist and are a part of our useful building stock. Many have brick deterioration related to masonry growth, and many have been restored including brick/mortar replacement and potentially movement provisions (i.e. movement joints). Depending on the type of damage, they may require basic maintenance, restoration, or a full assembly replacement.

Movement

The volume of a clay brick begins to change from the day it is installed on a building’s exterior. A wall of brick can expand and contract together, creating differential movement with other portions of the building, leading to stressing and then separation. The brick might be moving at a different rate than the adjacent stone masonry pieces, perpendicular to the brick on the other side of a building corner, or in the opposite direction of the structural elements supporting it. This discussion calls for a review of a few of the main sources of movement in masonry structures.

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Thermal expansion

Every material used in construction experiences movement when undergoing temperature change. This movement is persistent throughout the life of the brick masonry and cycles throughout the yearly temperature changes. Brick Industry Association (BIA) Tech Note 18 recommends using a thermal expansion coefficient of 7.2 x 10-6 mm/mm/C (4 x 10-6 in./in./F). For example, a 30.5 m (100 ft) wide wall will grow 12 mm (0.5 in.) when undergoing a 37.8 C (100 F) temperature change.

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Moisture growth

Clay fired brick masonry will never be dryer than the moment it is removed from the kiln. After that moment, the masonry will begin to absorb atmospheric moisture, as well as moisture from weather events until the masonry reaches equilibrium. BIA Tech Note 18 recommends using a moisture expansion coefficient range of between 3 x 10-4 and 5 x 10-4 mm/mm (in./in.), depending on the brick’s porosity.

Concrete shrinkage

Concrete theoretically cures forever; and during this cure process, some water is evaporating from the concrete, while majority of the water is reacting with the cement particles. Both evaporation and reaction cause the concrete to shrink, however, most of the shrinkage occurs within the first year after concrete is placed. This mode of movement is not relevant to mass masonry structures. Transitional and cavity wall masonry buildings with a concrete structure experience movement due to this phenomenon. ACI 209.1-05, Report on Factors Affecting Shrinkage and Creep of Hardened Concrete, gives a shrinkage coefficient range of between 2 x 10-4 and 8 x 10-4 mm/mm (in./in.). The shrinkage will vary based on the concrete mix design and environmental conditions.

There are additional sources of movement that can occur in masonry, most of which can be considered negligible. For the sake of this article, focus on the above three sources.

Table 1 is an example calculation of the possible vertical movement that can occur at a 30.5 m (100 ft) tall masonry veneer clad concrete structure. This fictional masonry was installed at a mean temperature of 26.7 C (80 F). After one year, when the team arrives on site during a sunny day, the masonry is approximately 48.9 C (120 F). What is the net movement at the top of the building?

Thermal

100 ft  ∙  4×(10^(-6)  in./in.)/(°F)   ∙   40 F=0.016 ft (0.192 in.)

30.5 m ∙  7.2 x (10^(6) mm/mm)/(°C)   ∙   22.2 C= 0.0049 m (4.9 mm)

 Moisture

100 ft  ∙  4× 10^(-4)  in./in.  =0.04 ft  (0.48 in.)

30.5 m  ∙  4× 10^(-4)  mm/mm  =0.012 m  (12 mm)

Concrete Shrinkage

100 ft  ∙ -5× 10^(-4)  in./in.  =-0.05 ft (0.6 in.)

30.5 m  ∙ -5× 10^(-4)  mm/mm  =-0.015 m (15 mm)

Table 1 mathematically demonstrates how every brick masonry clad building will move. Fortunately, there are a few typical options to address the movement. In new construction, builders install vertical movement joints in the masonry every 6 to 7.6 m (20 to 25 ft), with additional movement joints at openings in the brick and corners. These joints are typically 8.9 mm to 12.7 mm (0.375 to 0.5 in.) wide and provide space for the brick to expand without affecting the adjacent component. Horizontal control joints are installed at the floor lines, typically every or every other floor line. Engineered movement joints may be applicable when dealing with dynamic movement due to wind or earthquakes. This article will not be exploring movement due to dynamic loading.

Maintenance, restoration, and replacement

Without the movement provisions mentioned in the previous section, the clay masonry can expand and damage itself or other building components. If an existing building has movement related damage, those movement provisions can often be installed as part of the solution. The extent of repairs is determined by the extent of the damage. Repairs can fall into three general categories: maintenance, restoration, and replacement.

Maintenance typically includes repointing of cracked mortar and replacement of a small, discrete number of bricks. If an older building only has mild damage, simple maintenance can be a viable solution. Most of the moisture-related growth has already happened, and the brick only experiences temperature-related movement; therefore, the maintained building will have to contend with less growth than it originally did.

Beyond simple maintenance, restoration may be required and could include future provisions for growth (i.e. control joints) and/or securement of the existing facade (e.g. post-installed masonry anchors). Control joints are an appealing option because they can be easily installed and will relieve the internal stresses in brick facades.

Masonry anchors, such as helical anchors, mechanically engaged anchors, or adhesive anchors, can mitigate future movement and secure problematic areas before they become unstable. Movement joints cannot typically be installed through an entire mass wall without changing the bearing condition and the lateral load resistance. Masonry anchors are typically better suited toward mass walls because veneer walls typically have a concealed water-resistive barrier (WRB) on the backup wall. Masonry anchors would need to puncture this barrier to anchor to the backup wall. This may be an acceptable risk if the cavity wall did not have a WRB to start with, or if the installer can demonstrate that an anchor passing through the WRB does not pose a significant risk.

For extreme conditions, maintenance or restoration may not be sufficient and the brick will have to be replaced. This is necessary when the brick’s bearing or lateral stability is compromised. The following case studies examine situations which call for maintenance, restoration, or a full assembly replacement.

Case study 1: Wear and tear

An elementary school building constructed in multiple phases has a red brick facade. The majority of the facade has little deterioration, except on a mortar joint step crack on one of its abandoned chimneys. The building appears to have adequate movement capabilities for the brick, and the cracking is likely related to the use of the chimney and the furnace-related temperatures it was subjected to. Since the chimney is no longer in use and the rest of the brick is performing well, no other movement provisions are required for this repair. Solely repointing the mortar crack is appropriate for this condition.

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Case study 2: Relieving angle turned into a lintel

A university building was constructed in the mid-1950s with a red brick masonry cavity wall and a concrete superstructure. The cavity wall is typically 13.7 m (45 ft) tall and is dead loaded at the base of the structure (i.e. with no floor line relieving angles). It appears as though lintels existed above windows openings and extended 0-152.4 mm (0 to 6 in.) into the adjacent masonry. Figure 4 shows a typical elevation.

No movement provisions were provided at this building. Experts observed step cracking at window opening corners. They investigated these cracks by making exploratory openings, and what they found shocked them.

The relieving angles were set into shelf angle wedge inserts (Figure 5).

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Some of these lintels also extended up to 152 mm (6 in.) into the adjacent masonry piers. As the masonry grew due to moisture and thermal expansion, and the superstructure shrank due to concrete shrinkage, the masonry began lifting the relieving angle until the relieving angle support bolts hit the top of the wedge insert, turning the renovators’ relieving angle into a lintel. In some cases, the masonry continued to grow, lifting the masonry above the windows so it no longer bore on the newly converted steel angle.

Renovators came up with the following criteria to correct the issue:

• Bearing ≥ 25.4 mm (1 in.)—Do not modify the angle. As long as the bearing condition is greater than 25.4 mm (1 in.), the masonry piers can withstand the load imposed by the lintel.
• 0.0 mm (0.0 in.) < Bearing < 25.4 mm (1 in.)—Remove and replace the angle, provide a bearing of 101.6 mm (4 in.) minimum. If the bearing condition is less than 25.4 mm (1 in.), the masonry is at risk of crushing and spalling. Incidentally, renovators did not observe many of these conditions as the masonry had already spalled.
• Bearing < 0.0 mm (0.0 in.)—Do not modify the angle. If the angle never bears on masonry or if the masonry has spalled and is no longer there to bear on, the angle is simply bearing on the wedge insert and is back to being a reliving angle as the original designers intended.

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In addition to the above criteria, renovators cut new control joints to separate the masonry piers from the masonry above the window openings. They provided a new mortar joint to re-support the masonry assembly above the window openings, where the masonry had lifted. Additional restoration anchors, rust inhibiting paint, and new through wall flashings were also installed.

In retrospect, two design features in the original construction could have prevented this situation.

• The relieving angles should not have extended into the adjacent piers.
• Vertical control joints should have been installed between the masonry piers and the masonry above window openings.

Case study 3: Growing, growing, gone

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Part 1

A university building was constructed in the late 1960s with brick cavity walls and tall, multistory, industrial windows. The windows end beneath the top floor, creating a brick band that spans the entire 48.8 m (160 ft) elevation. No control joints were installed in this brick band at the time when the building was being constructed

Expandable foam and sealant joints were installed at the corners, possibly as an afterthought attempt to provide movement capability. In any case, the foam and sealant at the corner allowed the brick to expand freely past the adjacent corner brick. The 45.7 m (150 ft) length of brick expanded without restraint, and the brick moved almost a full inch past its corners.

While this brick expansion did not damage the adjacent corner brick, it did impact the brick anchors. During the investigation, the brick anchors on the extents of the 48.8 m (160 ft) brick band were found to be bent at almost a 45-degree angle. While the brick anchors were still engaged, they were being stressed to their limits along with typical wear and corrosion for a component of such an age.

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Since the brick ties were bent and overstressed, the lateral stability of the brick assembly was deemed insufficient. Installing new helical masonry anchors through the face of the existing brick assembly into the wall’s substrate was considered, but this would compromise the existing WRB behind the face brick. This left a full-on replacement as the only remaining option. Removing the brick allows an opportunity to install new brick anchors, repair/replace the existing membrane, and install new brick with control joints properly spaced out.

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Part 2

At an adjacent building on the university’s campus, a bump out addition was constructed in the late 1970s. Adjacent to the existing building, the addition’s facade was a 9-m (30-ft)-wide white brick cavity wall with no openings or control joints. At the edge of this wall, the brick wall turned 90 degrees for a short, 0.6 m (2 ft) return near the existing building.

A large vertical crack developed on the facade wall near the corner, and the small return section rotated away from the rest of the wall. The expansion of the 9 m (30 ft) wall had pushed towards the corner, which was resisted by the perpendicular brick creating stress. This stress was only relieved when the brick cracked vertically, effectively separating the corner from the rest of the wall.

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During their investigation, renovators noticed brick anchors were not installed near the corner or on the return wall. The only lateral stability the corner had was provided by the brick’s physical connection to the rest of the wall—with no anchors present and bricks starting to fracture, the wall’s lateral stability was compromised. Similar to Part 1, a replacement of the brick at the corner was the only viable option. Removing the brick allows opportunity to install new brick anchors, touch-up the existing WRB, and install new brick with an additional control joint.

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Conclusion

As seen in the three case studies, a wide range of repairs can be used to address brick movement driven deterioration. This may range from topical repairs to completely removing and reinstalling the masonry. Masonry is a historically proven construction technique able to last more than 100 years. As the industry focuses on sustainability and embodied carbon, building reuse becomes
a critically important topic. The most sustainable building is the one that already exists. Saving an able brick wall is an important concept to defend. Identifying walls that cannot be salvaged will also play a necessary role in building reuse. Brick has always been a popular choice and is engrained in our history and culture. Maintaining those walls creates an aesthetically-pleasing, watertight, and sustainable building.

Authors

Stephen Holland, PE, is an enclosure engineer at LeMessurier Consultants Inc. practicing in the greater Boston area. He has experience in the investigation, rehabilitation, and design of a variety of enclosure systems including roofing, glazing, masonry, cladding, waterproofing, and below-grade systems. He has specialized in the restoration and retrofitting of enclosure systems in existing and historic buildings. He serves as the present chair of the Boston Building Enclosure Council (B-BEC) and is an active member of ACE Mentoring.

Luke Niezelski, PE, joined the building technology division of Simpson Gumpertz & Heger Inc. (SGH) in 2014.  He is licensed as a professional engineer in Massachusetts and is experienced in the investigation/assessment, design, construction administration, monitoring/inspection and field-testing of historic and contemporary building enclosure systems.  He has been involved in various Boston high-rise construction projects and is routinely collaborating with architects, owners, and contractors on complex building enclosure designs.

Source URL: https://www.constructionspecifier.com/choosing-between-restoring-or-replacing-cracked-spalled-and-displaced-brick-facades/

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