It's been three months since Franz Ferdinand announced possibly the most polite departure of a founding member that popular music has experienced. 'We'd love to say this is a result of personal or musical differences, but it's not,' said the band in a statement at the start of June, which laid out guitarist Nick McCarthy's reasons for leaving. 'Those differences are what we formed the band around in the first place.'

Following the release of Franz's excellent collaboration with Sparks last year, FFS, the recording of the follow-up to their 2013 fourth album Right Thoughts, Right Words, Right Action is imminent. Yet McCarthy now won't be a part of it. 'I'm going to concentrate on production and writing some completely different things for a bit,' he said in the same statement, 'and we can all look forward to hearing the new Franz Ferdinand album.' Most pressing of all, one of the things he has to concentrate on is his young family; he and his wife Manuela Gernedel live in London now, and his main reason for leaving the band is to avoid being away from their young children for months at a time.

Handily combining child-raising with writing those completely different things, then, McCarthy's first post-Franz project is Manuela: a collaboration with Gernedel that takes her first name. A debut album is due but currently unscheduled for release on Johnny 'Pictish Trail' Lynch's Eigg-based Lost Map label. It's a suitable home, given the imprint's track record of releasing interesting and off-beam indie-pop. One track from the collaboration has so far been made public through Lost Map's site, the irresistible 'Cracks in the Concrete'.

A louche post-punk groove, it's immediately apparent what Franz Ferdinand will miss – McCarthy's steely, dramatic guitar-riffing – and yet Gernedel's vocal steals the show. It's warm but reserved, arch but involving, as she sings 'a baby was born in my house last night / and I dreamt of money and success', calling to mind Stereolab's Laetitia Sadier in her open-hearted cool. The album, when it arrives, will feature collaborations with Django Django's Jim Dixon, Mystery Jets' William Reese, Veronica Falls' Roxanne Clifford (herself another Glasgow émigré) and Franz drummer Paul Thomson.

Of course, to those who know their music, Gernedel and McCarthy's new venture has stronger roots in the pair's Box Codax project (alongside Alex Ragnew) than it does Franz Ferdinand. Responsible for the albums Only An Orchard Away in 2006 and Hellabuster in 2011, this was another outing with a strong collaborative element, with both Metronomy and the artist / musician Martin Creed involved in the latter album. The partnership goes back further than that; Gernedel and McCarthy were both brought up in Bavaria, Germany (she's from Austria originally, while he was born in Blackpool) and it's there they started dating and collaborating in 1999.

'We first met at a summer party in the local youth club in Rosenheim,' says Gernedel, of the town where they lived. 'Nick was playing free jazz with his band. I'd played guitar when I was a child but didn't keep it up, then as a teenager I played bass in a band. I've been singing with people on and off, and I'm a visual artist. I mainly make paintings and sculpture.' She is, in fact, the reason McCarthy was in Glasgow to form Franz Ferdinand in the first place. Although they were often described as an 'art school' band, only bassist Bob Hardy went to Glasgow School of Art. As did Gernedel, to study painting, which is why McCarthy moved to Scotland with her.

The couple both became embedded in the fertile art school / musician crossover scene in the city, though. Gernedel was in a band with Dixon, Clifford, sometime Franz member Andy Knowles and Celia Hampton named White Night, which released a single on Thomson's label (David Shrigley created the cover). Gernedel and McCarthy were married in Bavaria in 2005, then she moved to London in 2008, with him following after. 'It's been about eight years now, which is shocking,' she says. 'I thought we'd just stay for a year or two. Did we move for the weather or because we wanted to go somewhere else? I can't really remember … '

In London, she studied a Masters at Chelsea College of Arts, then worked as an art teacher for people with learning difficulties. 'I think it's more slow than music I've done previously, it's got a stoner vibe,' says McCarthy of the album, which was recorded in his Hackney studio, Sausage, and is due later this year. 'It became much more musical than I thought,' says Gernedel. 'I had something like spoken word in mind, with minimum instrumentation. But that's the magic of working with someone else.'

It's little wonder the record has arrived so quickly, because Sausage is like a second home to the couple. 'I spend most of my days there,' says McCarthy. 'It's pretty much been a dream of mine since I was 16, to have a room stuffed full of stuff to make music with. So that's what I'm going to do. And it gives me a chance to go home now and again to watch my children grow up and make me laugh.'

'Cracks in the Concrete' is out now on Lost Map. Manuela play Lost Map's Howlin' Fringe presents Future Echoes at Leith Theatre's Thomas Morton Hall, Edinburgh, Sat 1 Oct.