Tag Archives: 01 35 91−Historic Treatment Procedures

Preserving 10 Light Street’s Exterior Façade with Restoration

Photos courtesy RMF Engineering

Photos courtesy RMF Engineering

by John Hovermale, PE

One of Baltimore’s most visible and recognizable buildings is located at 10 Light Street, close to the waterfront. The 34-story structure is considered to be the first skyscraper in the city; it has remained its tallest building for nearly 50 years.

The construction of the tower started in July 1928 and was completed in 15 months. This is a remarkable feat given its magnitude—approximately 46,450 m2 (500,000 sf) and standing taller than 152 m (500 ft). The building also showcases a high level of architectural detail on its interior and exterior design. It is one of the historic gems of the Maryland Historic Trust, the City of Baltimore’s Commission for Historic Architectural Preservation (CHAP), and Preservation Maryland.

While the designer, Taylor & Fisher-Smith & May, and the builder, J. Henry Miller, created the iconic tower to last forever, age and natural elements necessitated efforts to reinforce and renew the exterior features so it could remain a prominent fixture in the commercial real estate market.

Baltimore’s skyscraper
The 10 Light Street structure has a steel skeleton frame with masonry wall construction comprising terracotta backup faced with brick and limestone. The floor slabs consist of a terracotta flat arch system common to the period. The structure type is known as a ‘transitional façade,’ which was often seen in the United States from the 1890s to the mid-1950s.

One of the several limestone medallions at the entrance – each medallion has a unique carving.

One of the several limestone medallions at the entrance – each medallion has a unique carving.

When structural steel became a common building material in the early 1900s, it allowed building structures to reach new heights. Transitional structures bridged the gap between those with load-bearing masonry barrier walls that preceded them, and the curtain walls common today. In transitional façades, the floor slabs and masonry walls encase the structural steel at the building’s perimeter. Generally, structural steel buildings, particularly buildings of several stories, tend to be flexible and move when subjected to lateral loading. The steel frame and masonry were not detailed to accommodate the differential movement. Additionally, traditional façades were not always properly designed to resist moisture infiltration.

The owner of 10 Light Street noticed cracks and dislocated masonry in the façade and knew if those issues were not addressed, they could progress, presenting a higher risk to public safety and resulting in expensive future repairs.

Assessing the damage
Baltimore-based RMF Engineering completed a detailed study of the façade to assess the project’s magnitude and set budgets. The condition assessment employed 29 swing stage drops providing close access to the façade for inspection. (Given the vertical nature of the work, ‘drop’ is the term used to describe the wall area accessible from a mast climber or swing stage.)

Not every square foot of the façade was inspected during the study; however, enough drops were completed to provide an assessment at each unique structural and architectural building detail, enabling reliable extrapolation of the data for those areas not inspected during the study.

Detail from the original architectural drawings. Image courtesy Taylor & Fisher-Smith & May

Detail from the original architectural drawings. Image courtesy Taylor & Fisher-Smith & May

RMF provided construction documents for the restoration work and followed through project completion as the construction inspector. More than 325 m2 (3500 sf) of the original Italian marble was replaced. Approximately 122 m (400 ft) of helical joint reinforcement was installed at vertical cracks in the brick, and 6800 helical pins were used to restore the limestone. Further, more than 4645 m2 (50,000 sf) of spot tuck pointing was completed, in addition to brick replacement, relief angle replacement, and structural steel reinforcement. The restoration was successfully completed with more than 35,000 hours of labor and no injuries.

The construction budget was set by the owner based on the condition assessment report. The delivery method was guaranteed maximum price (GMP). Although there was a detailed study, the inherent risks and unknowns related to façade restoration work remained. The GMP approach provided for better cost management where funds can be focused on the most critical repairs, as well as shifting funds from low-to high-priority repairs to address unforeseen conditions. Funds can also be shifted from repairs that were conservatively estimated in the design to other areas. Moreover, the GMP process allows the owner, engineer, and contractor to evaluate the approach to each repair and determine a solution addressing design and constructability.

Throughout the construction of 10 Light Street, RMF inspected each drop with the contractor and reviewed the remedial work required, providing an opportunity to verify what was illustrated on the construction documents and make adjustments where necessary. If conditions varied from the construction documents, the owner was immediately notified and a discussion about costs and procedure followed. After the contractor completed the work on the drop, RMF would punch out the drop and document the findings. Although a final walk-through was performed for the entire project, most of the project was punched out on a drop-per-drop basis as the façade access migrated along the building.

Logistics
Access to perform the repairs was one of the project’s most challenging aspects. The building has a straight vertical face for the bottom 22 floors, accommodating the use of mast-climbers. However, the floor plate diminishes and steps back several times between Floor 22 and the top of the building with a number of small roof levels in the upper section making mast-climbers impossible to use. Individual swing stages of various lengths, including small, single-cable stages called ‘buckets,’ were used. In a few isolated areas, bosun chairs were the only solution. More than 60 drops in all were required.

The building is located in a busy area of the city with a bus stop on one side of the structure and a service entrance on the other—both had to be maintained throughout the construction. Scaffolding with overhead protection was erected over all the sidewalk areas from the face of the building to the curb line of the streets; this also provided a landing level for the mast climbers and swing stages above the sidewalk level.

The design was completed in a phased approach, and the construction documents were separated into three packages:

  • Package 1–Marble Replacement;
  • Package 2–Phase 1, General Repairs; and
  • Package 3–Phase 2, General Repairs.

The Marble Replacement Package was completed first given the replacement stone had a long lead-time. The team determined the stone thickness and the overall quantity the contractor needed to order. While the stone was being quarried, cut into 30-mm (1.18-in.) thick slabs and shipped, the initial mast-climber was being erected at the first drop. This marble removal provided valuable information on the conditions of the existing backup, and also provided insight on the appropriate stone anchorage details subsequently added to the Marble Replacement Package.

A before and after photo of the repair performed at a steel spandrel beam. The moment splice plate behind the screw jacks is needed for the new steel member installation. [CREDIT] Photo courtesy RMF Engineering

A before and after photo of the repair performed at a steel spandrel beam. The moment splice plate behind the screw jacks is needed for the new steel member installation. Photos courtesy RMF Engineering

10light_spandrelbeam_after

Repair plans
The original stone was an Italian marble containing intermixed serpentine, and classified as Soundness Group D by the Marble Institute of America (MIA). Soundness Group D stone is often the most attractive but, it is the least durable of the Groups A through D and contains large portions of natural faults and variations.

Although prized for its rich burgundy color and decorative veining, it is not suitable for exterior exposure in this climate. As a result, all the exterior marble was replaced. This same marble, used extensively inside the building and a few well-protected exterior areas, was in good condition. It maintains its polish and gives credence to the deleterious effects on the marble when exposed to the elements over time. The replacement stone used on the project is not a marble product, but rather a granite quartzite stone from a Brazilian quarry. The granite quartzite is highly durable and an excellent visual match to the original marble.

The stone was mounted in two distinct conditions:

  • recessed into the wall with a limestone surround; and
  • mounted in a steel frame integrated into the window system as a spandrel panel.

The primary methods of attachment for the recessed stone were stainless steel drop pins in the surrounding limestone at the upper section, epoxy-set stainless steel pins at the bottom section, and blind stainless steel Type 31 anchors in the brick backup.

The pin locations had to be carefully placed to logistically allow the stones to be set onto the epoxy pins at the bottom and tilted into place with tight tolerance all around. The recessed stones have unique shapes; this required the stone supplier to field measure and make templates of each individual piece given the tight tolerances. The stone fabrication rate was largely driven by the accessibility to the façade to allow for field measurements and template-making.

This is the original marble in the framed opening. Not only is there a crack in the panel to the right along one of the natural soft veins in the stone, but the marble had also lost its luster and burgundy color.

This is the original marble in the framed opening. Not only is there a crack in the panel to the right along one of the natural soft veins in the stone, but the marble had also lost its luster and burgundy color.

New granite quartzite in framed spandrel panel.

New granite quartzite in framed spandrel panel.

This existing marble at the main entrance was replaced in the ornamental brass framing.

This existing marble at the main entrance was replaced in the ornamental brass framing.

 

 

 

 

 

 

 

 

Additionally, the stone fabrication had to be closely coordinated with the mast-climber and swing-stage sequence. At the spandrel panel installation, the external steel components that held the stone in place were re-installed or replaced with new steel components matching the existing profile to maintain architectural integrity. All steel components were cleaned and painted with a high-performance direct-to-metal acrylic coating. Missing from the original design, a weep system was added directly above the sill frame to prevent water buildup behind the stone. A fluid-applied air barrier membrane was installed on the brick backup in all cases.

The Phase 1 and 2, General Repair Packages included repairs to the limestone and brick with the Phase 1 Package including higher priority repairs. Funds left over after completion of Phase 1 were attributed to the Phase 2 scope of work.

The limestone was on the bottom five floors and the building’s upper portion between Floors 19 and the top of the building. Less than one percent of the ornamental limestone pieces (e.g. medallions, rosettes, and carved lion heads) required patching. The limestone pieces not mechanically anchored to the backup or keyed into the backup or other limestone proved to be an issue—a few of the stones had shifted out of place. After removing the stone for inspection during the report phase, the joint mortar and mortar buttered on the stone’s back were found to be the only mechanisms holding it in place.

Although this performed well for numerous years, the mortar joints were deteriorated and allowed moisture to migrate behind the stone, slowly loosening them. While consideration was given to removing and re-anchoring without impacting the face of the stone, the risk of removing stones of this size on a swing stage, particularly with heights upward of 122 m (400 ft), was too great.

This is one of many limestone lion heads on the 22nd floor.

This is one of many limestone lion heads on the 22nd floor.

The decision was made to keep the stones in place, re-align if necessary, and anchor with helical pins through the stone’s face. The small circular recess left in the face of the stone from the drill at each pin was patched with a mortar specifically designed for a natural stone substrate. The patching product was also tinted to match the limestone color. In addition to the pinning, all of the limestone joints were raked out and repointed. The new mortar was made compatible based on petrographic examinations and chemical analysis on the existing mortar—a critical step in any façade restoration work. The results yielded ASTM C270, Standard Specification for Mortar for Unit Masonry, Type M or S to be suitable. The existing brick mortar was also tested resulting in ASTM C270 Type S.

Given its age, the original brick’s condition and mortar between Floors Five and 22 was good—there were only a few areas where the brick was repaired and re-pointed. The steel lintels at the window openings were also in good condition. In the upper elevations of the building, where the building geometry becomes more complex with the extensive use of limestone, the brick and mortar was more distressed. The abrupt change in the façade condition would suggest the several building setbacks, roof levels, and parapets allowed the building envelope to take on more moisture in the upper elevations which also experienced rust-jacking in some of the steel columns and lintels.1

The façade damage caused by rust-jacking areas was addressed, including remediation of the structural steel. The brick was removed in front of the steel where the rust-jacking occurred to expose the steel for inspection. Although the column steel experienced some section loss, it remained structurally adequate. However, some lintels and spandrel beams needed to be replaced. Switching out the short lintels was straightforward, but the spandrel beam replacement presented challenges in providing temporary support of the wall and roof structure during the beam remediation.

Ultimately, the existing beam stayed in place and a portion of the outboard flanges of the existing beam was removed. A new steel member was installed with a similar depth and narrow profile allowing one wythe of brick to bypass the new steel. Given the existing beam’s condition and selective removal of the flanges, structural calculations were performed at each phase of the construction to verify adequate support of the wall and roof structure throughout the process. The vertical cracks in the brick caused by rust-jacking of the steel columns were repaired using L-shaped helical joint reinforcement recessed into the horizontal mortar joints. The reinforcement was spaced vertically at 0.6 to 1.2 m (2 to 4 ft) on center (oc), and wrapped around the corner to stabilize the brick. The cracked brick was replaced and the area repointed. The limestone integrated into the corner masonry was pinned to the backup.

A falcon head on the 29th floor.

A falcon head on the 29th floor.

Conclusion
Façade issues are frequently left unaddressed until a major disaster occurs, or until the damage is so extensive it becomes cost-prohibitive to repair. The 10 Light Street façade restoration project is an excellent example of proactive façade inspection followed up with repairs in order to successfully preserve an historic structure.

For its first 84 years, the building served primarily as a banking center, and provided retail and office space for thousands of employees, customers, and visitors every day. It is currently under renovation to be repurposed as a residential complex with tenant fit-out and building support functions on the lower three floors. Approximately 460 living spaces will be integrated into 31 floors of the building, ranging in size of approximately 42 m2 (450 sf) for the studio units to 186 m2 (2000 sf) for the multiple bedroom and loft units. These apartments are primarily designed for the student population attending nearby teaching hospitals and universities, and are expected to be ready for occupancy in 2015.

Notes
1 Rust-jacking is the process where steel, in contact with masonry, corrodes then expands pushing the masonry outward to the point where the masonry cracks and can eventually become dislocated. (back to top)

John Hovermale, PE, is a partner in the structural engineering department at the Baltimore branch of RMF Engineering Inc. He has been with RMF for 20 years, and has been involved in façade restoration projects for a decade. Hovermale has a bachelor’s degree in civil /structural engineering from the University of Maryland, College Park. He can be reached via e-mail at john.hovermale@rmf.com.

Putting a Fresh Face on Historical Façades: Project teams

Hallidie Building Project Team
Owners: Edward J. Conner and Herbert P. McLaughlin
Owner’s Representative: The Albert Group Inc.
Architect of Record: McGinnis Chen Associates
Preservation Architect: Page & Turnbull Inc.
General Contractor: Cannon Constructors
Surface Preparation Shop Coatings and Field Applicator: Abrasive Blasting & Coating (ABC) Inc.
Specialty Engineering and Testing: Professional Service Industries Inc.
Coating Consultants: Amos and Associates

ZCMI Project Team
Owner: City Creek Reserve Inc.
Engineer, Surface Preparation, and Primer: Historical Arts & Casting Inc.
Architect: Hobbs & Black
General Contractor: Jacobsen Construction Company Inc.
Field Applicator: Daniels Painting
Coating Consultants: Protective Coatings Intermountain Inc.
Miami County Courthouse Project Team

Owner: Miami County
Architect: John Ruetschle Associates Inc.
Engineer: Historical Arts & Casting Inc.
Construction Management Team: Cast Iron Restoration Management
General Contractor: Shook Construction Company
Shop Applicator: Brian Painting Company
Field Applicator: E.B. Miller Company
Coating Consultants: Ohio Coating Consultants

To read the full article, click here.

Putting a Fresh Face on Historical Façades

Photo courtesy Robert A. Baird/Historical Arts & Casting Inc.

Photo courtesy Robert A. Baird/Historical Arts & Casting Inc.

by Jennifer Gleisberg

Across the country, communities are preserving and restoring historically significant architectural façades recognized for ornamental sheet metal and cast-iron features such as colonnades, domed roofs, cornice sections, dentil blocks, frieze panels, and pendants. Many historical façades dating back to the second half of the 19th century have been neglected and damaged from impacts, moisture intrusion, corrosion, or flawed castings.1

Water intrusion resulting from the absence or failure of adequate waterproofing systems often leads to deterioration of not only the structural steel, but also the clips, brackets, and fasteners used to attach ornamental components. Fissures, or pitting in cast iron or other decorative metal pieces, can also trap moisture and airborne corrosive materials, causing oxidation or rust to occur over time.

Restoring these landmarks to like-new condition requires craftsmanship, technical expertise, and high-performance coating systems that comply with demanding standards for aesthetics, durability, and resistance to corrosion and ultraviolet (UV) light.2 This marriage of skill and technology is especially evident in the three projects highlighted in this article:

  • San Francisco’s Hallidie Building;
  • Zions Cooperative Mercantile Institution (ZCMI) cast-iron storefront in Salt Lake City, Utah; and
  • the cast-iron domed roof façade of the Miami County Courthouse in Troy, Ohio.

The Hallidie Building’s curtain wall
After 2.5 years of remediation work, the iconic Hallidie Building’s main façade was complete. Architects involved with the project were McGinnis Chen Associates and preservation architects, Page & Turnbull. Additional specialists involved with the restoration included a materials scientist, sculptor, testing agency, structural engineers, curtain wall consultant, and coatings consultant.3

Named for Andrew S. Hallidie, the inventor of the cable car and a regent at the University of California, the building was listed in 1971 on the National Registry of Historic Places and the San Francisco Historic Landmarks and Districts. Originally designed by Willis Polk and constructed in 1917–1918 by the University of California, the building is noted for its glass curtain wall façade, which was considered unique for its time, but has now become a common element in modern architecture.4

The building is described in San Francisco: Building the Dream City, in the following passage:

The glass façade was hung, curtain like, away from the actual structural frame of the building, in a separate frame of elaborate cast iron, with ornate fire escapes at either side. The ornamental iron fretwork relieves the cold severity of an all-glass wall, and the result is highly decorative.5

Annie K. Lo, LEED AP, project manager for McGinnis Chen Associates, was responsible for evaluating, labeling, photographing, and documenting each piece of the building’s curtain wall, frieze panels, ornamental balconies, and fire escapes. She explained the uniqueness of the glazed curtain wall at the time of construction is significant. Considering available technology in 1918, Polk was inventing something, rather than using an example to model after.6

Numerous challenges were encountered with the Hallidie Building’s water-damaged structural steel, corroded frieze panels of stamped zinc, and ornamental fire escapes and balconies. At the time of construction, sealants or flashing with adequate waterproofing were not available. Also, the design did not support metal expansion and contraction normally required in a curtain wall.

Phase I of the restoration involved removal, repair, and reinstallation of approximately 735 sheet metal and railing components for the ornamental balconies and fire escapes, along with 360 windows around the perimeter of the curtain wall façade. Phase II of the project, completed April, involved the removal, repair, and reinstallation of the remaining 153 windows in the curtain wall.

For the project team, getting to Phase I was a challenge, explained Lo.

“We started working with the city and the Historic Preservation Commission on obtaining approvals to remove the metal pieces since this was a salvage and disassembly project for a notable landmark building,” she said. “Each piece had to be tagged and given an identification number so it could be tracked throughout the repair process and reinstalled on the building.”

Originally, the project’s architects envisioned restoring the frieze panels by making spot repairs to severely corroded sections. This repair methodology was changed after the existing lead coatings were removed and the severity of damage to the panels was determined. The back side of the panels was reinforced with a spray-applied layer of fiberglass, which enabled more of the original historic material to be salvaged.

More than 90 years of exposure to water caused damage to the structural steel and decorative metal of the Hallidie Building façade. Photos courtesy Annie K. Lo/ McGinnis Chen Associates

More than 90 years of exposure to water caused damage to the structural steel and decorative metal of the Hallidie Building façade. Photos courtesy Annie K. Lo/ McGinnis Chen Associates

Another change involved the method used by the coating applicator to remove the multiple layers of lead paint that had built up over decades. Early in the project, it was envisioned the paint would be removed by dipping pieces into a chemical stripping solution. However, this method proved too slow and did not provide the cleaning needed to apply a zinc-rich, aromatic urethane primer.

Due to the fragile and thin condition of ornamental cornice sections, dentil blocks, frieze panels, and pendants, these components were prepared in accordance with Society for Protective Coatings/NACE International–The Corrosion Society (SSPC-SP6/NACE) No. 3, Commercial Blast Cleaning, prior to the application of the primer. Window frames, window sashes, metal grates, and railing sections were prepared in accordance with SSPC-SP10/NACE No. 2, Near White Blast Cleaning, before priming with the same zinc-rich coating.

Structural steel used to support the ornamental balconies was so badly corroded from water infiltration it could not be salvaged or reused and had to be completely replaced.

Removal of ornamental metal was carefully monitored for compliance with environmental regulations, in accordance with Section 02085, Federal and State Occupational Health and Safety Administration (FED-OSHA) 29 Code of Federal Regulations (CFR) 1019, 1025, and California-OSHA under Title 8, CCR 1532.1, which relates to the proper capture and disposal of lead-based paint.

All surface preparation and paint removal was performed in blasting chambers offsite. The exterior coating system for both ornamental metal and structural steel consisted of a spray-applied zinc-rich primer, an aliphatic urethane intermediate coat, and a fluoropolymer topcoat in both satin and semi-gloss finishes.

The coating system was selected to achieve the highest level of performance in terms of color retention and longevity. Keeping the associated costs in mind, the durability and lifespan of the coating system was an important concern. A zinc-rich primer offering a high level of corrosion protection on bare metal was specified for the project. When this is applied with a proper intermediate coat, additional corrosion protection is attained.

Fluoropolymer topcoats offer aesthetic performance, gloss retention, and protection against UV light and climate conditions. The coatings were custom-matched to the building’s original colors. The project’s preservation architectural firm conducted a coating analysis that involved scraping down to the original first and second coatings and matching them to a Munsell color card, which was then provided to the coatings manufacturer.

Blue and gold were the original colors used on the building and the coatings created through the color match were accurate. Originally, a gold coating resembling true gold leaf was used on ornamental sheet metal and designers were able to replicate this. Once the ornamental metal pieces were reinstalled onto the curtain wall, coatings were used to touch-up welds and scratches.

Early this year, the Hallidie Building project was named winner of the Charles G. Munger Award at the annual Structure Awards sponsored by the SSPC. The award is presented to an outstanding industrial or commercial coatings project demonstrating longevity.7

This is the Hallidie Building before its architectural façade restoration.

This is the Hallidie Building before its architectural façade restoration.

The Hallidie Building is one of the world’s first glass curtain-wall buildings. Photo © Sherman Takata, Takata Photography

The Hallidie Building is one of the world’s first glass curtain-wall buildings. Photo © Sherman Takata, Takata Photography

Restoring the ZCMI façade
Recognized as one of the earliest department stores in the nation, Zions Cooperative Mercantile Institution was founded by Brigham Young in 1868. The structure’s three-story, classical cast-iron façade was constructed in three separate phases, beginning with its center section in 1876, followed by an extension to the south in 1880, and a north addition in 1901. The façade was placed on the National Register of Historic Places in 1970 and was subsequently listed on Salt Lake City’s historic register.8

Cast-iron façades were popularized throughout the second half of the 19th century due to their fire-resistant properties and ability to replicate sandstone and limestone. In addition to providing structural support to upper floors, cast iron also allowed large display windows for merchandise, allowing light into the building’s interior.9

In 1971, plans for a new downtown mall had called for demolition of the original building, including its cast-iron façade. A coalition of the Utah Heritage Foundation and community preservationists was successful in saving and restoring the façade to become part of the ZCMI Center Mall. Restoration architect Steven T. Baird was enlisted to develop procedures for dismantling, reconditioning, and reconstructing the façade from 1974 to 1976. Working primarily out of his garage, Baird is credited with creating the model for other cast iron renovation efforts across the country.10

The 23 x 43-mm (75 x 140-ft) ZCMI façade is now attached to the west face of Salt Lake City’s new Macy’s department store. [CREDIT] Photo courtesy Robert A. Baird/Historical Arts & Casting Inc.

The 23 x 43-mm (75 x 140-ft) ZCMI façade is now attached to the west face of Salt Lake City’s new Macy’s department store. Photos courtesy Robert A. Baird/Historical Arts & Casting Inc.

More than three decades later, the company owned and operated by Baird’s sons—Historical Arts and Casting Inc.—was commissioned to restore the façade a second time as part of the mixed-use redevelopment project. Today, the landmark façade fronts the west face of Salt Lake City’s new Macy’s department store.11

Measuring 23 x 42 m (75 x 140 ft), the façade consists of cast-iron colonnades with 63 bays for windows and openings, a cornice section made of galvanized sheet metal, and thousands of mechanically fastened ornate castings. For both restoration projects, each component was carefully numbered, cataloged, and moved offsite for reconditioning or replacement.

Restoring historical cast-iron façades like ZCMI presents major challenges. Cast iron’s ability to replicate stone was enhanced by mixing sand into paint, which was then applied in thick coats to the casting. Locating fasteners under several layers of old paint was a challenge during the first restoration in the 1970s. Additionally, many of the façade’s original cast-iron components were severely deteriorated due to moisture penetration and had to be recast.12

The preferred method for removing old paint from cast iron is blast-cleaning in accordance with SSPC-SP6/NACE No. 3, followed immediately by the application of a primer to prevent surface rust. Since most old paint found on historic cast-iron façades contains lead, blasting debris must be captured and disposed of in accordance with U.S. Environmental Protection Agency (EPA) regulations (e.g. 40 CFR Subchapter 1, “Solid Wastes.”13

When surface preparation uncovered pitting or other imperfections in the cast iron, a surfacing epoxy to recondition the surface, followed by zinc-rich aromatic urethane, and intermediate epoxy primers that doubled as a field-applied tie coat, were used. Structural steel used to secure cast-iron components to the building was blast-cleaned and primed by the fabricator with a zinc-rich aromatic urethane primer.

The façade’s galvanized-metal sections were prepared in accordance with SSPC-SP1, Solvent Cleaning. Abrasive blasting was originally tried, but the sheet metal was too thin; therefore a chemical stripper on the metal was used and it was then pressure-washed.

The cornice sections were shop-primed with a polyamide epoxy coating, followed by a finish coat of high-solids fluoropolymer coating specified for its ultraviolet (UV) light stability and durability. Four custom colors were specified, including a metallic gold that mimicked 24-karat gold leafing. An acrylic polyurethane metallic clearcoat was applied over the metallic gold finish wherever it was used.

The cast-iron façade on Zions Cooperative Mercantile Institution (ZCMI) consists of thousands of ornamental components assembled together on columns.

The cast-iron façade on Zions Cooperative Mercantile Institution (ZCMI) consists of thousands of ornamental components assembled together on columns.

During reassembly and the application of field coatings the façade was surrounded by scaffolding and enclosed to help control environmental conditions. Tie-coats, fluoropolymer finish coats, and gold accent finishes were brush-, roller-, and spray-applied to the cast-iron colonnades and ornate castings then reattached to the façade by screws using detailed drawings as a guide.

Approximately 2300 work hours and 1892 L (500 gal) of coatings were needed to complete the field coatings and installation, which was completed in the spring of 2012.14

Bringing order to the Miami County Courthouse
The decorative exterior of the Miami County Courthouse in Ohio, constructed between 1885 and 1888, was also restored. The original Greco-Roman design by Joseph Warren Yost featured four corner domes, a central dome, and four pavilions built of cast-iron cladding over riveted iron frameworks.15

After nearly a century, the building’s decorative cast iron had severely corroded due to water intrusion, which threatened the building’s interior courtrooms that had been renovated in 1982. In 1989, an architectural firm was contracted to conduct a condition survey that included a preliminary specification for what would eventually become the largest restoration of cast-iron construction in the country.16

In 1995, the county retained a construction management team to oversee the project. The following year, a local construction company was awarded the primary restoration contract, which called for dismantling and restoring the cast iron from the building’s five domes and four pavilions. The contract also called for replacement of the building’s slate roof, copper flashing, windows, exterior lighting, copper statues, and clock tower.

Before cast-iron components could be removed, more than 18,143 kg (40,000 lb) of pigeon waste and other debris was taken from the belfry. The disposal of this material followed the same guidelines as removal of asbestos or lead. 17, 18

Rather than prepare the cast iron for recoating onsite, it was prepared, primed, and given an intermediate coat offsite. Once the material was returned and reinstalled, the field touch-up and finish coats were applied.

Coating consultant Dan Haines compared the removal of cast-iron components to “an architectural dig”—each piece of the cladding was cataloged using a numerical coding system identifying the exact location it needed to be reinstalled.

Crews worked from scaffolding and used an exterior elevator lift to move more than 15,000 cast-iron pieces, which were dismantled and taken offsite in phases to be reconditioned or replaced. Historical Arts and Casting was responsible for recasting more than 50 percent of the severely corroded cast iron, requiring more than 700 patterns to be manufactured.19

It was determined a lack of sufficient waterproofing led to the failure of the decorative cast iron on the courthouse, so replacement pieces were molded with flanges and lap joints enabling moisture to run off rather than collect on the surface. Vertical and horizontal joints were caulked with a silicone system to prevent water penetration and adhesion testing was conducted to verify the coating system’s ability to bond to the prepared cast-iron components.20

Both replacement parts and reusable cast-iron components ranging in weight were prepared in accordance with SSPC-SP6/NACE No. 3, Commercial Blast Cleaning, and shop-primed with a zinc-rich aromatic urethane primer. They also received a shop-applied intermediate coat of polyamide epoxy coating.

Structural iron was cleaned and field-coated with a high-build modified polyamidoamine epoxy coating. Once the shop-primed cast-iron cladding was reinstalled, it received a field-applied coat of a light gray aliphatic acrylic polyurethane topcoat, followed by a urethane clear coat. 21

Cast-iron cladding that covered the domes and pavilions of the Miami County Courthouse was dismantled and removed to an offsite location for restoration or replacement and recoating. [CREDIT] Photo © Mike Ullery

Cast-iron cladding that covered the domes and pavilions of the Miami County Courthouse was dismantled and removed to an offsite location for restoration or replacement and recoating. Photos © Mike Ullery

Built in 1888, the Miami County Courthouse was listed on the National Register of Historic Places in 1975.

Built in 1888, the Miami County Courthouse was listed on the National Register of Historic Places in 1975.

 

 

 

 

 

 

 

 

 

 

 

 

Conclusion
The restoration and preservation of historically significant sheet metal and cast-iron façades requires the special skills and expertise of craftsmen and professionals who share an understanding and appreciation of these architectural treasures. These specialists spend countless hours assessing the condition of structural and ornamental metalwork, dismantling components, removing old coatings, and restoring or replacing thousands of individual pieces. Given the exhaustive amount of work and care involved with restoring these national landmarks, specifiers must rely on high-performance coating systems that offer long-term substrate aesthetics and protection against corrosion caused by moisture intrusion, UV light, and thermal cycling.

Notes
1 The resource is written by J. Waite, AIA, with an introduction by cast-iron preservationist Margot Gayle. See, Preservation Briefs, “The Maintenance and Repair of Architectural Cast Iron,” 1991, Technical Preservation Services, National Park Service at www.cr.nps.gov/hps/tps/briefs/brief27.htm. (back to top)
2 Important standards include ASTM D4060, Standard Test Method for Abrasion Resistance of Organic Coatings by the Taber Abraser; ASTM D4141, Standard Practice for Conducting Black Box and Solar Concentrating Exposures of Coatings; ASTM D4587, Standard Practice for Fluorescent UV-Condensation Exposures of Coatings; and ASTM B117, Standard Practice for Operating Salt Spray (Fog) Apparatus.  (back to top)
3 For more, visit American Institute of Architects (AIA), San Francisco Chapter’s website at www.aiasf.org/about/history/hallidie-renovation/. (back to top)
4 For more, see Business Wire’s news release, “San Francisco’s Urban Design Community Celebrates Restored Hallidie Building” at www.businesswire.com/news/home/20130501006221/en/San-Francisco%E2%80%99s-Urban-Design-Community-Celebrates-Restored. (back to top)
5 See J.B. Alexander’s, San Francisco: Building the Dream City (Scottwall Associates, 2002). (back to top)
6 This comes from an interview with Lo in April 2013. (back to top)
7 Visit, Durability + Design’s article, “Curtain Wall Project Earns Accolades,” at www.durabilityanddesign.com/news/?fuseaction=view&id=9002. (back to top)
8 Visit www.downtownrising.com/DTR-media/city-creek/downloads/ZCMI_Facade_Fact_Sheet.pdf. (back to top)
9 See Note 1. (back to top)
10 See Salt Lake Magazine’s article, “Restoration 2.0,” by J. Pugh. Visit www.saltlakemagazine.com/blog/2012/01/12/restoration-20/. Historical Arts and Casting also has a video, ZCMI A Legacy Cast in Iron. (back to top)
11 For more, see City Creek Reserve’s news release, A Familiar Face Returns to Main Street: ZCMI Façade is Back at www.downtownrising.com/DTR-media/city-creek/downloads/ZCMI_Facade_Release.pdf. (back to top)
12 This is from an interview with R. Baird in April 2013. An interview was also conducted with M. Call in February 2012. (back to top)
13 For more, see R. Baird and Historical Arts and Casting’s “Restoring Cast Iron Facades (Part 1),” at www.historicalarts.net/restoring-cast-iron-facades-part-1-of-2/. (back to top)
14 This is also from an interview conducted by the author with M. Call in February 2012. (back to top)
15 For more see R. Baird and Historical Arts and Casting’s “The Rebirth of A Cast Iron Gem (Part 1).” (back to top)
16 See Note 15. (back to top)
17 For more see R. Baird and Historical Arts and Casting’s “The Rebirth of A Cast Iron Gem (Part 2). (back to top)
18 This is from an interview conducted with D. Haines in April 2013. (back to top)
19 See Note 17. (back to top)
20 See Note 17. (back to top)
21 See Note 18. (back to top)

Jennifer Gleisberg is an architectural sales coordinator for Tnemec Company Inc., where she provides support for sales and marketing of protective coatings for concrete, steel, concrete masonry unit (CMU), dry wall, and decorative cast iron and sheet metal substrates used on historical landmarks. She is an active member, or has received credentials, from NACE (NACE Coatings Inspector – Level I Certified), The Society of Protective Coatings (SSPC), and the United States Green Building Council (USGBC), where she is a Leadership in Energy and Environmental Design (LEED) Green Associate (GA). With more than 10 years of experience in the coatings industry, Gleisberg brings a customer service perspective to architectural projects that require coating solutions for lasting aesthetics, as well as protection from corrosion, impact and abrasion. She can be contacted at gleisberg@tnemec.com.

To read the sidebars about the project teams, click here.