Digital craftsmanship in stone design

by Katie Daniel | May 10, 2017 2:18 pm

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by Dan Rea
Modern technology has made its mark on stone design as well as fabrication. Today, project teams taking advantage of technology are experiencing increased freedom in control of the design concept, from development through to fabrication. Additionally, many improvements in quality control and greater accuracy of the stone’s shaping, final fit, and finish are possible.

High-tech fabrication techniques, including 3D modeling, sandblasting, and computer numeric control (CNC) capabilities, are changing stone fabrication. While the technology to accomplish this is advanced, it is not cost-prohibitive. Further, the process reduces fabrication time, often making custom designs more cost-efficient to achieve.

An overview of case study examples—including a church in Virginia, a museum in the capital, and a Boston hospital—demonstrates how technology enables realization of a design team’s vision.

3D modeling assists renovation
Renovation projects where existing materials and designs must be matched can bring a host of challenges technology can help meet. A case in point is the St. Francis of Assisi Catholic Church renovation in Staunton, Virginia, completed by architect Frazier Associates. The church needed to replace an existing limestone façade, and its serpentine, hand-built design presented a reproduction challenge. Granite fabricated with exact precision through modern 3D modeling technology provided the ideal solution to preserve the Franciscan legacy in the community.

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The church was constructed in 1895 to accommodate Staunton’s booming Irish Catholic population. To pay tribute to the parish’s Irish heritage, a green limestone was selected for the Gothic-style building. More than 100 years later, the limestone had deteriorated to such an extent, safety had become an issue. Catch-guards were necessary at various locations around the church to intercept falling stones. Renovation was imperative, so the church initiated fundraising efforts and began making plans to provide a match to the existing architecture and create a durable structure able to stand the test of time.

The original green limestone was no longer available, but church members desired that the new stone to remain in the same color family as the old. A material with a longer lifespan was also desired. The church began searching for a close match to the existing limestone and found a proprietary green granite to be an ideal material. The granite’s supplier and fabricator also offered the technology necessary to replicate the meandering existing pattern. In 2013, to provide a visual representation of the end result, the granite supplier and fabricator provided a mockup of the project in this granite for the church to place on display.

The church’s exterior renovation finally began in the spring of 2015. Originally built by hand, many of the limestone pieces were not square, and joints varied in size. Correctly matching the existing pattern presented a true challenge.

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To replicate the twisting pattern of the 120-year-old stones, the granite fabricator employed 3D scanning technology. A complete scan of the church produced a 3D model, which was then converted into the 2D documents, in turn used to trace the pieces. Next, the fabricator used the 2D drawings to create a 3D model. These extensive efforts ensured the new façade would replicate the existing one with accuracy.

Despite the advanced scanning technology, some details could not be detected from the outside of the church. For example, some areas of the building were not visible from the ground, where the scan was performed. To meet this challenge and fully duplicate the pieces, photos and field measurements were taken. Piece size and joint variations were reconciled during the drafting process.

This technology was essential when looking for replication of an existing appearance in a restoration project. The other option would have been to provide blanks or sticks to the jobsite and have everything cut to fit onsite. However, with lack of space and continued use of the church, this was not a viable option; the staging area for this project was a small parking lot.

In total, 6706 granite pieces—each measuring 65,550 mm³ (4 ci)—were produced and installed at St. Francis of Assisi, which was completed in May 2016. Bishop Francis DiLorenzo celebrated with a mass to commemorate the renovation’s completion. The years of planning, fundraising, and execution were worth the wait, and St. Francis remains one of the most beautiful structures in downtown Staunton—a heritage preserved for many years to come.

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Modeling and CNC shape museum hardscape
In September 2016, after nearly 10 years of planning and fundraising efforts, the Smithsonian Institution opened its new museum in Washington, D.C. The National Museum of African American Culture and History (NMAAHC) is the only museum dedicated to documenting the history, lives, and culture of African Americans. It features granite hardscape elements, which relied on 3D modeling technology and CNC fabrication.

Located on a 2-ha (5-acre) site on the National Mall—between the National Museum of American History and the Washington Monument—the museum encompasses 29,970 m² (322,600 sf), with five levels above-grade and four below.

The museum’s design is distinctive among other structures on the National Mall. Its façade consists of 3600 customized, cast-aluminum panels known as the Corona. These bronze-colored panels call to mind the craftsmanship of enslaved workers in the pre-Civil War cities of Charleston and New Orleans, and create a distinctive impression for NMAAHC, representing traditional African architecture. Three architecture firms—the Freelon Group, Davis Brody Bond, and SmithGroup—worked on the museum.

Just as the museum’s architecture makes a unique design statement, its landscape design also distinguishes it among nearby museums and monuments, incorporating it into the larger configuration of the National Mall. According to GGN, the project’s landscape architect, “The site is designed to encourage visitors to extend the museum experience outside and to linger and reflect on the important narratives being told within.”

Granite played an important role in meeting the project’s design goals, about 3437 m² (37,000 sf) of black granite in various finishes was used for hardscape elements such as paving, wall facing, wall coping, steps, curbs, benches, and bollards. Most of the stones for the project were modeled in 3D software, which allowed the fabricator to coordinate with the landscape architect and ensure the designs met expectations. Due to the project’s complex nature, an extensive amount of coordination between the fabricator’s drafting team and the architect was needed to ensure the 3D models were accurate before fabrication. Once the design team approved the fabricator’s drawings and models, the fabricator converted them into a file for use on a five-axis CNC machine.

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CNC technology was critical for creating the intricately crafted cubic wall of black granite encompassing the site’s perimeter. Most of the museum’s walls feature a highly polished finish, but a combination of polished coping and honed granite finish was selected for its north wall, which also serves as the main entrance. This wall spans approximately 103 m (340 ft) across the front of the museum, running parallel to Constitution Avenue. The less-polished finish was selected due to concerns over too much reflection off the wall at the highly traveled entrance.

Fabrication of the granite pieces for the north wall proved particularly challenging because of the wall’s slight radius and continuous bullnose. The fabricator had to produce each of these stones at precisely the same thickness to ensure an exact alignment at installation. Most of the wall’s cap pieces were milled by the fabricator’s five-axis CNC machine, then finished by hand to create the bullnose. With multiple workers applying a bullnose to hundreds of pieces, accomplishing the precision required for alignment required an exceptional level of coordination and craftsmanship.

Varying finishes were also used for additional granite elements at the site. The museum’s bench seats employ a polish finish, and the curbing features the same honed granite finish as the north wall. The paving—encompassing 2322 m² (25,000 sf) of granite—and stair treads use a proprietary slip-resistant finish.

Modeling most of this project in 3D software allowed the fabricator to coordinate with the architect and make sure all parties were getting exactly what they wanted prior to fabrication. Using 3D drawing capabilities for a project like this provides virtually endless possibilities, and can help streamline the fabrication process.

Sandblasting achieves intricate imagery
When a project’s design calls for images to be etched into stone, high-tech sandblasting capabilities can bring the artist’s vision to life. Such was the case with the granite entrance to Boston Children’s Hospital, where an intricate dot-matrix stenciling and sandblast process transferred an artist’s images to polished gray-black stone. The architecture firm for this project was Mikyoung Kim Design.

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Titled “Playful Nature in the City,” the 111-m² (1200-sf) L-shaped wall greets visitors to the hospital with playful images of animals and foliage. The intricate ‘hide-and-seek’ design includes dragonflies, butterflies, and flowers, and provides a different view with each experience.

To achieve the complex etchings, the stone fabricator took the artist’s images in a vector format and then converted them to a mask, which was applied to the stone. Through the sandblasting process, various shades of gray were produced and recessed into the stone. White paint provided highlights and added depth.

More than 200 pieces of granite were created, with unique images on each piece. Each adjacent piece had to be carefully laid out and lined up to ensure the image flowed correctly across the entire wall.

Stone selection is a critical decision for a sandblast project. Typically, a dark-colored stone is used to create an effective and necessary contrast against the images inscribed into the stone. At Boston Children’s Hospital, black granite provides such a contrast, offering the ideal background to allow images of animals and foliage to shine through. Additionally, this granite’s grain structure and stark gray-black color appeal to many artists. The stone’s consistent appearance in many different finishes allows designers to achieve a contrast in color without the use of different stones. In addition to the feature entrance wall, the project includes more than 167 m² (1800 sf) of surrounding curbing in the same stone.

Conclusion
As designers continue realizing the benefits of technology, the demand for digital craftsmanship in stone design is expected to rise. The abundance of equipment in the marketplace will likely lead to lower prices. As such, the design world will have more opportunities than ever to see fine, detailed stone work in more market segments and more applications. Ultimately, the industry will see more use of sustainable, natural stone materials in project design.

Dan Rea is senior vice president of sales and marketing for Coldspring. He is also a member of MIA+BSI: The Natural Stone Institute, and served as president of the Marble Institute of America (MIA) in 2015. He can be reached via e-mail at drea@coldspringusa.com[7].

Source URL: https://www.constructionspecifier.com/digital-craftsmanship-in-stone-design/

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