Artist at work: Inside the workshop of Ron Mueck, creator of eerily lifelike sculptures

It has taken Ron Mueck two years to complete three new sculptures for the show at Fondation Cartier in Paris next week. This he has done almost completely silently.

Ron Mueck doesn't speak when he is working. He listens to other people talking on the radio, and to the background of noises that filter in from the north London street outside: sirens, footsteps on the pavement, buses. This is what he has always done, but his army of fans and critics wouldn't know that, because Mueck doesn't give interviews, won't talk about his influences or his processes, and eschews the media, leaving his work to speak for itself.

Which it does in the form of giant sculptures of humans crowding into gallery spaces (like A Girl, an enormous new-born, still bloody from birth), or shrunken versions of people in perfect proportion (Dead Dad, a small sculpture of his deceased father, sprouting Mueck's own hair). Whatever their size, his works become vortexes, sucking all the air into their clay and resin frames, their force to be lifelike uncannily strong. They are less sculptures than versions of humanity, with their flabby folds of skin, hair sticking out of pores, hard toenails and tangible sheens of sweat.

Now, for the first time, the public can see Mueck at work, despite his intense regard for privacy. With the strict clause that there would be no interview, the artist allowed his friend and colleague, the photographer Gautier Deblonde, to film him making his new sculptures. Deblonde's documentary – his first, and showing as part of the new exhibition – will cause rumblings in the art world and beyond: his access to Mueck is unprecedented and spans two years, a couple of days each week in the studio. Deblonde worked on the film like a photographer – static camera on tripod – and never created scenarios, just filmed Mueck working.

"What struck me was how quickly they come alive," he says of the sculptures. "The first part is the clay, and this is almost like the negative of his work: all the details you need to have a human body alive. That's the first half of the film, and he's very slow – because he knows when he gets that right, then the sculpture will be good." Mueck uses the clay as a mould for the resin, which makes the final sculpture: the clay is destroyed in this process, so it has to be absolutely perfect, or he has to start all over again.

Deblonde recalls days of watching Mueck prepare the clay, making what seemed like the same movement again and again. "It was quite meditative." This is the core of Mueck's process, hence the solitary daily task – his two assistants don't help until after the mould is cast. The resin, Deblonde says, makes the sculpture more human, but by then Mueck has already given it life: it already has its own feeling and attitude.

There has always been a deep poignancy to Ron Mueck's sculptures, with their microscopically detailed imperfections. His newest works are just as arresting in their immediacy. In one, Mother and Baby, a mother wearily carries shopping bags, her expression blank, as the infant, foetal within the confines of her buttoned-up coat, stares up at her. Young Couple, capturing a man's sinister grip on his companion's wrist, draws attention to a silent moment of pain, and suggests a world of it beyond. And then the older pair, Couple on the Beach, where imperfections of age are writ large across their epic proportions –yet within a skin that is terrifyingly alive, there is a sense of peace in their expressions.

"You still don't understand how Ron makes it work," Deblonde says of his documentary. It's not a technical, step-by-step instruction manual, he cautions. It's a film about time spent, about the smell and feel of a workshop, about some kind of metamorphosis through endeavour. "You see him working on a piece of clay and suddenly this person appears. Somehow, out of his hands, he manages to create an object – alive."

Fondation Cartier, Paris, Tuesday to 29 September; fondation.cartier.com