In an industrial area just outside Grand Rapids, there is a machine at a new company called Mangrove that lays down sand, injects it with cement paste through nozzles as thin as a pencil lead, and, over the course of about nine hours, prints a batch of furniture that would be impossible to cast in a traditional mold. No mold is required. No rebar or reinforcements, either. Just sand, cement, water and a plasticizer, deposited layer by 2.8-millimeter layer until a bench, a fire pit or a sculptural table emerges from what is essentially a giant sandbox.
Though Mangrove is new, it is built, its founder says, on three decades of precast concrete experience and a chance discovery out of Italy.
Over roughly three years, Mangrove CEO Greg Kerkstra tracked the development of the Italian concrete printing technology that would become Mangrove’s foundation, watching it mature until it was ready to take to market. Mangrove bought the first machine and shipped it to Michigan.
There is a novelty to 3D printed concrete furniture, which is designed for the hospitality market, outdoor spaces at corporate headquarters and the home, but the technology allows for so much more. Mangrove has a catalog of products it makes, but the company can 3-D print in concrete just about anything a designer can come up with. It is also open to working as an OEM for other furniture makers or industries.
“The opportunities are going to be found for many years as we explore this world,” Greg Kerkstra said, pointing to architectural details and landscape pieces that “never could be done, or it used to be done, but now it’s so expensive” because the skilled tradespeople who once built them by hand are gone. He also framed the environmental case in personal terms, contrasting it with a career spent watching concrete precast waste pile up. “Here we recycle the sand, which is the form,” he said. “There’s really very little to no waste at all. It’s revolutionary.” The company has grown from two employees a year ago to 16 today, including Nathan Kerkstra, Greg’s son and Mangrove’s president.
Nathan Kerkstra is bullish on the range of markets the printer opens up, from landscape furnishings to architectural work, and frames the company’s role as translating designers’ ambitions into something buildable. “We want to keep building on the excitement and not let the designers’ ideas die on the screen. We want to turn them into reality.” Mangrove is the exclusive North American partner for Progress Group, the Italian company that developed the technology, and Nathan Kerkstra said the plan is to “create the blueprint here in Grand Rapids” before expanding, with room already reserved in the building for a second machine.
Shawn Orr, Mangrove’s director of operations, walked a group of visitors through the mechanics of it all. While not going too deep into technical jargon, the process is known as SPI — selective paste intrusion. A print head studded with 0.8-millimeter nozzles moves across a bed of sand, opening and closing nozzles independently to inject a Portland cement paste and formulated with a Sika admix in between the sand particles. The sand left uninjected simply falls away later; there’s no support structure to build or remove, because the loose sand holds the part up while it cures. “This printer is the first of its kind in North America,” Orr said, one of only three in the world running the technology.
That’s the trick, and it’s why Mangrove can print shapes like lattice work, L-shaped forms and honeycomb-like structures. A cast or mold could never produce products like this economically. A full job box — 8 feet wide, 5 feet deep, 16 feet long — takes roughly nine hours to print at a 60-second cycle per pass, then cures for about 12 hours before products are pulled from the sand. Compression testing has shown strengths of up to 6,500 psi, Orr said, without any steel reinforcement. Orr described the cement mix, once it hits the print head, as having “the consistency of thick chocolate milk,” which makes it thick enough to build a wall, yet thin enough not to clog a nozzle less than a millimeter wide. Color is handled the same way. Four sacks of pigment get introduced at the mixer in whatever combination a customer wants, though colors are limited.
Brian Grysen, Mangrove’s director of sales, said the concrete 3D printer is now the center of an entire commercial model. That model splits three ways. There are standard products designed and engineered in-house, products designed by an Italian collaborator and printed by Mangrove, and custom work for projects where a mold or cast simply doesn’t work. “We think there’s a gap between custom, completely custom, hand carved and something that’s made out of a cast or a mold,” Grysen said, arguing that Mangrove lives in that space where a minimum order quantity is too small to justify a $20,000 or $40,000 mold.
Distribution runs through existing reps who already call on landscape architects and hospitality buyers, plus a retail push through outdoor living dealers. There’s also a direct e-commerce site, something the company can support without loading down operations, since there are no molds to warehouse.
Since the products are made of concrete, they are extremely strong. Grysen doesn’t dodge the freeze-thaw question that any concrete product that is placed in a cold weather location invites. “We actually put that fire table into a freezer overnight and got it down to -10 degrees,” he said, then heated it to 170 degrees and watched for micro-cracking. None appeared.
In the design studio, Lead Industrial Designer Spencer Hope described a process that starts with questions, not sketches. Mangrove strives to understand end users and learn about the environment the product will go into because a Mangrove piece is meant to last a lifetime.
The 3D printing allows furniture products to become architectural products. “I think we have a technology that’s doing things that have never been done. One of the opportunities is to start questioning those lines and categories themselves,” said Hope.
Aaron Vander Veen, Mangrove’s director of technical services, put it more concretely: Because the printer isn’t limited by formwork, the company can print any aesthetic shape — a column, an arch — sidestepping the cost that makes those forms rare in traditional precast. “We can actually become the form,” he said, describing how Mangrove can create an aesthetic first and then figure out afterward “how we fill structurally or we wrap structurally.”
Though Mangrove is a relatively new company, the family has deep experience in the concrete industry. Greg Kerkstra traced the company’s roots back to his father, Larry, who started Kerkstra Precast in 1963. The company was known for its precast wall panels, hollow-core floor plank, beams, columns, parking structures and architectural precast. After his father retired from the business and Kerkstra Precast was sold to Fabcon in 2021, the family, which seems to have concrete running through their veins, needed a new idea, which came in the form of Mangrove and 3D printing concrete.
Since the technology allows Mangrove to make just about anything out of concrete, the company is already being pulled into different markets, including those they never expected. A group recently approached Mangrove to create artificial coral reefs using 3D printed concrete.
