Cara Mertes, director of the Sundance Institute Documentary Film Program (DFP), is an award-winning former executive producer of PBS's documentary showcase P.O.V. who knows only too well how unforgiving the non-fiction arena can be. For every Michael Moore, Morgan Spurlock and Alex Gibney there are thousands of film-makers whose stories will struggle to see the light of day.

Mertes recently presided over the Documentary Edit and Story Lab (a part of DFP's year-round support initiative) that ran in Utah (June 21-28). It helps four film-makers with editing and post-production; armed with wise counsel and a grant, the film-makers then leave to complete their projects.

"There's nothing quite like this in the world, where you leave everything behind and form a community working on each other's projects," Mertes said during a recent break from the lab, now in its sixth year. "The fellows in the June lab have all made enormous progress and it's been a privilege to put this together. But it's tough - I have four films at the lab and none of them has representation yet."

"It's about opening up one's creative process to trusted people who have gone through this themselves," says Laura Poitras, a June adviser and former participant. One of this year's film-makers, Natalia Almada, who was invited to take part in the June lab with El General, an account of her great-grandfather and former Mexican president Plutarco Elias Calles, says the lab was "super intense" but "helped me focus on the heart of the film and strip away the things that get in the way of the story".

Being invited to a lab is no guarantee a film will screen at the Sundance Film Festival or air on the Sundance Channel. Mertes can make suggestions to festival director Geoff Gilmore - nine DFP titles including Trouble The Water and Be Like Others made it into last January's festival - but she warns: "We don't want to cross those lines."

One of the first decisions Mertes made after she arrived as DFP director three years ago was to allocate a "major production grant" to the June 2007 lab project Trouble The Water from Carl Dean and Tia Lessin, longtime Michael Moore collaborators. Their account of the impact of Hurricane Katrina told through the eyes of a New Orleans rapper went on to win this year's documentary grand jury prize at the Sundance festival and was picked up by Zeitgeist Films in the US. "People didn't understand why this film had to be made, but we were always believers so their story would not get lost," Mertes says.