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Stone Panels International in Marble Falls constructs buildings that reach for the sky

Stone Panels International in Marble Falls

In a conference room at the Stone Panels International LLC headquarters in Marble Falls, Greg Terhaar (left), vice president of sales and marketing, and Mike Day, president and chief operating officer, display examples of the kind of work done at the SPI plant. The stone display on the left shows a finished product. In the center is a 'honeycomb sandwich' with aluminum honeycomb on the outside and 3 centimeters of stone on the inside. The stone is split in half to make two panels. Next to that is an example of the hardware attached to the panels for installation to a building’s exterior walls. Staff photo by Suzanne Freeman

EDITOR’S NOTE: A story on the history of Granite Mountain that ran in the October 2019 issue of The Picayune Magazine sparked interest in what kind of work happens there now. Here’s the answer to that question.

A New York City skyscraper lies flat, end to end, up one side and down the other of a massive metal building on the outskirts of Marble Falls.

Inside the beige walls of an innocuous rectangular structure on Ranch Road 1431, slabs of St. Hubert limestone from Portugal go through different stages of processing before being crated and shipped to a construction site on East 54th Street in Manhattan.

In total, 35,000 square feet of stone — around 700 slabs weighing about 1,000 pounds each — will be processed down to the channel hardware that will hook it all together and form a high-end residential building in the world’s most exclusive real estate market.

“We call it puzzle-by-number,” said Greg Terhaar, vice president of Sales and Marketing for Stone Panels International LLC, a subsidiary of Coldspring, the quarrier that owns and operates Granite Mountain in Marble Falls. “Every piece has a number and specific location on the building, so, in a sense, the contractors put it together like a puzzle.”

Entire buildings are shipped from Marble Falls to job sites around the world, though most go to the biggest markets in the stone-cladding industry: Washington, D.C., New York City, and Chicago.

Coldspring, which has owned Granite Mountain since 1951, purchased SPI in 2016. The Dallas-based stone cladding supplier moved its headquarters to Marble Falls in 2017. Coldspring is headquartered in Cold Spring, Minnesota, and operates about 30 quarries in the United States, nine of them in Central Texas.

Terhaar and SPI President/Chief Operating Officer Mike Day both moved from Minnesota to Marble Falls with the Stone Panels acquisition. Terhaar is a 20-year veteran of the quarry company. Day has been on the job for 18 months. Both brought their families and their visions for growth.

“The external cladding industry is a $5 billion industry,” Day said. “Stone represents about 10 percent of that. SPI is a $25 million company, and we think it has the chance to be twice that.”

Stone Panels International in Marble Falls
Sergio Najera of Granite Shoals has 36 years’ experience working for Coldspring at Granite Mountain in Marble Falls. Here, he sands a return, or corner, for a skyscraper being built on East 54th Street in Manhattan. Staff photo by Daniel Clifton

At the company’s processing plant at 2400 RR 1431 West in Marble Falls, Terhaar gave a tour to demonstrate how rock becomes a skyscraper in the 21st century. The process involves giant machines, precise engineering, computer calibration, a top-secret recipe, and old-fashioned craftsmanship.

The creation of SPI’s StoneLite® panels begins with stone slabs of about 3 centimeters thick. They are laid flat on the rollers of a Simec machine that dominates one side of the cavernous plant. Reclaimed water and specially made bricks and brushes grind down the surfaces to a texture that will enhance the upcoming bonding process.

The next steps are proprietary but can be summed up as a baking process that involves bonding aircraft-grade aluminum honeycomb to both sides of the stone slabs.

“It all makes a honeycomb sandwich,” Terhaar explained. “The stone is in the middle, the honeycomb on either side. Then, it’s cut right down the middle so that one piece of stone becomes two pieces, ready to be sized and fitted to the project.”

Now that the 3-centimeter thick slabs of limestone have been divided in two, they can be picked up by just about anyone, certainly a construction worker on a job site. What used to weigh 20-30 pounds per square foot now only weighs 4-6 pounds.

“That’s a huge difference,” Day said. “The true value of the proposition is the speed and ease of installation. You don’t necessarily need a mason, and you don’t need a crane.”

A waist-high assembly line moves slabs along metal and yellow plastic rollers from station to station, where workers drill holes for hardware that is then attached and glued to the backsides.

“Here’s where the real artistry begins,” Terhaar said. “Now, we are going to make it look like it’s a natural, dimensional stone.”

If the stone needs a corner, called a return, it is cut from the same piece of stone at just the right angle and then reattached with a bonding agent. Slabs with returns glued on are moved to a table, where Sergio Najera of Granite Shoals waits with a handheld sander. With 36 years’ experience at Coldspring, Najera and his crew grind down the edges until the corners look like they are part of a solid piece of rock.

By this point, each slab has been marked with a part number and an address to its final destination. The back channels, which look like long steel tracks for mining trains, are pre-shipped and attached to buildings before the stone cladding arrives. Once the facade of the project arrives on site, installers can easily attach each numbered piece to the back channels, one after another, for 50-plus stories, right up into the New York City skyline.

Karla Conners of Horseshoe Bay guides a slab of St. Hubert limestone from Portugal through the process of attaching its channel hardware. Conners has worked at Granite Mountain for 34 years. Staff photo by Daniel Clifton

SPI processes more than granite and limestone for more than skyscrapers and state buildings.

“StoneLite® is used for everything from elevator interiors to external cladding on hospitals, universities, and high-end commercial and residential buildings,” Terhaar said. “We work with marble, limestone, sandstone, granite, travertine, slate, shipped here from around the world.” 

That’s not all that happens at the mountain.

While SPI prepared this particular skyscraper for construction, Coldspring workers were cutting 1.2 million cubic-feet of Sunset Red granite from the mountain for a jetty being built in Corpus Christi. In addition, behind the main processing plant, a diamond wire cut through a huge chunk of dimensional Sunset Red for use in a Capitol building project in Austin.

Stone Panels International LLC currently employs about 70 people at the Marble Falls location, a number that is growing, according to Day and Terhaar.

“We are always looking for good people to join our team,” Day said. “We have a great culture here, and we are working to enhance that culture. It’s a people-centric company. That’s the reason I moved here.”