For just 40 minutes in July 2019, children and adults played together on either side of the ugly wall that divides the United States from Mexico, at an especially gloomy stretch known as Sunland Park. Three shocking pink see-saws had been inserted through the fencing — not for long, but long enough for a film to be made that has since continued to be viewed by millions around the world. In it, people with huge smiles bounce up and down, dissolving the constraints of the barrier between them. If ever a meaningful moment was made for Instagram, this was it. Last Monday, the project, known as the Teeter-Totter Wall, was voted the overall winner of the Beazley Designs of the Year 2020 in the London Design Museum’s annual round-up of creative excellence.

The see-saws were the work of Ronald Rael and Virginia San Fratello, a pair of architects for whom the profession has provided a springboard for social and ecological activism, rather than a desire to make tall buildings. They first devised the idea of a binational see-saw in 2009, and it later made it into a book called Borderwall as Architecture. The US/Mexico wall has been an ongoing project since 2006. “So there was a certain amount of curation in the timing,” says Rael. “2019 was the moment of the heightened tension about child separation. Trump was waging his war on immigration, and the whole world was paying more attention.”

Rael and San Fratello paid for the project themselves (“It cost a few hundred dollars”) and spent weeks researching the feasibility of pushing their long pink metal poles from one side to the other, and screwing them into place, with an operative team on either side of the fence. “We knew we had five to seven minutes,” says San Fratello, “until the border guards would start to arrive.” On the day itself, children jumped on to the see-saws’ bicycle seats as soon as they appeared. When the border guards arrived, they simply stayed in their trucks.

“And then the kids got bored,” says Rael, who promptly removed the equipment as soon as the kids were done. The visual metaphor is an enduring one, though: that an action on one side of this border affects what happens on the other. “It is about trade and labour balances,” says San Fratello. “There has to be trust on both sides.”

When I speak to the pair, they are in southern Colorado. This is where Rael is from. “It was,” he explains, “the most northern part of Mexico, which is now part of the US. So I identify as indigenous, with roots to Spanish colonialism.” San Fratello comes from a family with Sicilian roots, though long resident in rural Georgia. “We live in the urban century, with urbanist ideals,” they say, “but personally we don’t adhere to a rural-urban divide.”

This, along with their architectural training, is key to their range of projects. Columbia, from where they graduated in 1998, was the first school to run a paperless architecture studio. “We were thrown into really sophisticated digital tools being developed and used in Hollywood,” they tell me. While their peers went off to LA to make state of the art movies, Rael and San Fratello took their avant-garde skills in another direction. “We work with digital technology, particularly with 3D printing, but within the natural world.”

While both have professorships (San Fratello at San Jose, Rael at Berkeley), in their studio in Oakland, California, they run a number of companies. One is Emerging Objects, where they experiment with the possibilities of transforming materials, such as mud and salt, into a substance that can be 3D-printed into usable parts, such as bricks and tiles, or objects such as plates and pots.

Another is Forust — a manufacturer of 3D printed wood. “You hear all about the forest fires in California,” says Rael. “So we’re finding ways to turn the results of that, and of other wood waste, into new products.” Their explorations into salt — “Such a beautiful material,” says San Fratello, “however thick or thin you print it. And so resilient as a possible building material” — have created flurries of interest in the Middle East, where desalination plants are producing tonne upon tonne of excess. And this summer, they succeeded in building tiny dome-like houses by 3D printing mud. “A low-cost prototype, a proposition for the future.”

With an organisation called Secore, they are investigating the rehabilitation of coral reefs, dropping dainty little 3D-printed forms into a carefully researched zone. The forms are made in concrete and ceramic and in a number of shapes proven to be the most attractive to coral larvae. “They’re like egg hatcheries,” says San Fratello. “And the coral larvae are the client. We’ve learnt that they like a slightly rough surface.”

What they themselves really seem to like is telling stories. “That’s a rural tradition,” says Rael. “And unlike architecture with a capital ‘A’, with a good story, you don’t know where it starts or stops.”

Next week, for example, on February 6, they will launch a new initiative called Hornos Tras Fronteras, or Ovens across Borders. For this, they will be constructing ovens like huge beehives out of local mud along the US/Mexican border — the first in a migrant shelter in Nogales, Sonora, where between 300 and 700 people live. “These ovens can provide hundreds of loaves, and let people in difficult circumstances feed themselves,” says Rael. “But my grandmother was cooking on an oven like this, just three generations ago.”

Not as cute as a pink see-saw, then, but this time built to last.