In August 2006, the Avalanches’ record label issued a press release trumpeting the imminent release of the Australian collective’s second album. The follow-up to Since I Left You had already started to take on a vaguely mythic status. It had, after all, been six years since their debut album had become a vast critical and commercial success. It spawned both a string of hit singles and a succession of reviews that boggled over the painstaking work and imagination that must have gone into making it: more than 3,500 samples meticulously stitched together into a seamless hour of music. The band’s driving force, Robbie Chater described it as “60s-influenced, inspired by Phil Spector and the Beach Boys, but using dance music techniques”. Its appeal wasn’t just the technical wizardry involved. The music on Since I Left You had a weird emotional pull to it – some of it was euphoric, some of it was funny, but a lot was suffused with an infectious wistful melancholy – that led people to start writing articles describing it as their all-time favourite album or too good to follow up.

The album’s tone might have had something to do with the circumstances of Chater’s life in the run-up to its making. “I started having a problem with alcohol when I was about 14 or 15. It’s been a lifelong thing, way pre the band,” he says. “By the time I was 21, I’d been a heavy drinker for a long, long time and my body was in a really bad way. I had a severe withdrawal issue, and ended up in intensive care for a number of weeks. I nearly didn’t make it, basically. Since I Left You came maybe two years after that, when I was sober and just glad to be alive. That’s a lot of the feeling and the joyousness behind that album – me at 23, making music and just happy to be alive, you know?”

But virtually nothing had been heard of the Avalanches since the legendarily chaotic live performances the band put on to support its release in 2001 had ground to a halt, bar a couple of remixes and some DJ dates at a tiny bar in their hometown of Melbourne. Still, their label insisted in that 2006 press release that the wait was worth it: Since I Left You’s successor was “sounding like everything we dared hope for and so much more. They’ve made the record of their lives.” A few months later, the band themselves chipped in. “It’s a really thrilling time for us now as this record comes together,” they said in January 2007. “It’s so fuckin’ party you will die, much more hip-hop than you might expect.”

Down the phone from his home in Melbourne, Chater lapses into what you might describe as a thoughtful silence, eventually punctuated by a long and equally thoughtful “errrrm” when reminded of this grand announcement. “Well, in our minds, I think we thought we were close to finishing it,” he says, eventually. “I remember around that point, we actually thought: ‘It’s just around the corner.’ Maybe we had so much music hanging around that it felt like a record was inevitable. Maybe we just needed to believe that it was really close, to keep us going. But looking back now, we were kind of nowhere near.”

You can say that again. It has taken the Avalanches 10 years to release their second album, Wildflower, a decade punctuated by a succession of further statements, all of them assuring fans that the album would be with them any minute. Today, Chater and Tony Di Blasi – who, depending on what day it is and which story you believe, may or may not be the last remaining members of a band that in some old photos numbered seven or eight – run through them with a combination of bemusement and rueful laughter. “Yeah, I’m just trying to think back to that one,” says Chater, considering a 2011 announcement that the album was “finished and they’re celebrating”. “Actually, I think that one might just have been a lie.”

When Wildflower was finally announced for real last month, via an interview on Zane Lowe’s Beats 1 show, the ever-positive former Radio 1 DJ suggested that its protracted gestation sounded “like the most brilliantly fun 16 years”: a decade and a half of carefree musical tinkering, aided by guest artists ranging from rapper Danny Brown to Father John Misty and punctuated by intriguing-sounding side-projects. There was music for a stage version of King Kong that opened in 2013 and a film intended to be “a kind of stoner hip-hop cartoon for adults” that foundered when the Avalanches’ record company refused funding, not unreasonably suggesting that they might like to get on with finishing their overdue second album instead.

An alternative view has been provided by Chater himself, who has described Wildflower’s making, with admirable Aussie bluntness, as “seven shades of shit”, variously involving financial meltdown, serious illness, experimentation with powerful hallucinogenic drugs, the departure of band members, the collapse of their record label and Chater’s insistence on using the same equipment that they’d made Since I Left You with, on which he’d stored umpteen musical ideas. “He had all this music recorded using a program called StudioVision,” sighs Di Blasi. “They stopped making the software in 1998. You can only run it on one of those old beige Mac computers, from before they’d invented the iMac. We literally had to carry it from studio to studio wrapped in towels and blankets because it was so ancient and fragile and about to break, plus the only monitor it would work with was this old thing that, no shit, weighed 30 kilograms. So we’d have to lug that up and down stairs. It was horrible.”

Did you ever think the album wasn’t going to get finished? “Yeah, for years and years,” says Di Blasi. “There seemed to be so many things that would happen that would kind of stop it, or something would come up, or we couldn’t quite solve the puzzle. It just permeated my mind, the thought that it was never going to happen. We always had that drive – ‘we’re never going to give up’ – but there was always that little voice in the back of my mind, going: ‘No, it doesn’t matter how hard you try, it’s not going to happen.’ That’s finally just gone away.” He gives a mordant chuckle. “About two weeks ago.”

They insist the problem wasn’t the shadow cast by their debut album, although it’s hard not to draw a link between its ever-swelling reputation. While they were working on Wildflower, Since I Left You went from being merely successful and acclaimed, to being listed as one of the best albums of the Noughties, to being hailed as an influence by everyone from Jamie XX to Animal Collective and performed as if it were a piece of classical music at the Sydney Opera House. There are stories of Chater and Di Blasi producing hundreds of different mixes of each track they recorded, of the duo becoming fixated on the most minute sonic details – “You want the sound of a dog barking,” says Chater, “but it has to be the right dog barking” – of them taking so long to finish tracks that the deals they struck with the artists they’d sampled on them expired and had to be renegotiated. The album went through endless permutations in search of a direction – from “dreamy George Harrison-type drone things” recorded with Luke Steele of the Sleepy Jackson and Empire of the Sun back in 2003 to straight-up hip-hop to “ambient world music”. Although, in fairness, the duo say that fragments of all of them ended up on the finished product: even the aborted stoner cartoon yielded Noisy Eater, featuring rapper Biz Markie, and the impossibly gorgeous sunshine pop of Harmony, with Mercury Rev’s Jonathan Donahue on vocals. One guest artist after another was called in: Connan Mockasin, Swedish indie star Jens Lekman, Ariel Pink, August Darnell, better known as Kid Creole of … and the Coconuts fame, none of whom actually ended up on the finished product. They became transfixed by “outsider music”: wildly obscure, privately pressed records by artists no real label in its right mind would touch. Wildflower is thick with samples of high school bands, amateur street musicians and figures such as deranged scat vocalist Shooby Taylor, the self-styled “Human Horn” and “beatnik monster comedy folk” singer Robbie The Werewolf. “It was a whole world I’d been previously unaware of,” says Chater. “This stuff that most people would consider junk, but to me was filled with feeling and personal spirit and realness and truth. You know, these people felt they had to make music no matter what. It just sort of fitted with our journey in a way: we were always going to do this album, and neither of us know what else to do except music, you know?”

Robbie Chater at the Field Day Festival in London in June 2016. Photograph: Richard isaac/REX/Shutterstock

Not all of the Avalanches felt that way: eventually, Chater and Di Blasi’s fellow founder member Darren Seltmann gave up and left. “Tony and I were just vibing off the stuff we were doing, making music,” says Chater. “Darren was a couple of years older than us, a baby daughter came along, he was just entering a different phase of his life. We let him know he was always welcome, but I think he probably realised: ‘This second record is going to take a long time, I want to have a family and I want a steady income.’”

He could see Seltmann’s point about money, he says. “Making this album became really tough financially. We had good friends and family who helped us, our management in the UK helped a lot financially, it became like a giant Kickstarter project. We maxed out credit card after credit card. We want to go on the road to enjoy the world, to meet amazing people and travel and share this new music with them, but it’s also the only way we can make an income and get out of debt.” He laughs. “Without wanting to sound too mercenary about it.”

There were other problems. At one juncture, Chater became ill with not one, but two auto-immune diseases that put him “out of action for three years”. At another – “a time of my life when I was, I dunno, searching for something,” as he puts it – he decided to undergo a three-week long course of ibogaine, a potent hallucinogen used by followers of the African spiritual discipline Bwiti and, controversially, as a treatment for heroin addiction. “There was a lady up in Northern Australia who’d got some from Mexico. You build up day by day until the final night where you have what’s called a flood dose, a massive, massive dose of ibogaine and you can be violently ill and hallucinate for 48 hours. It was a wonderful experience. It’s very confronting. You’re faced with certain truths about yourself and because they’re coming from within, the realisations that you’re having on this trip, there’s no arguing with them. They’re core, solid truths about yourself. It was quite shattering; frightening.”

They say they had a kind of spiritual breakthrough moment a couple of years ago. “We just learned to let go of songs we really loved that didn’t sit on the album, stop being very analytical and over-thinking, realise that something created in two minutes can be as worthwhile as something you’ve slaved over for two years, to let this album become what it was always meant to be,” says Chater. They came up with a structure – “it starts in a kind of hyper-realistic urban environment, then goes on a road trip to the sea or the desert or the countryside, while you’re on acid. So you start in the city and over the course of the record you end up somewhere far away from there, high as a kite” – and “the whole thing just started to flow”.

Even so, there were more problems. Their record label Modular collapsed while they were mixing the album, further delaying its release. With Wildflower completed and the first, generally ecstatic reviews rolling in, the Avalanches were set to embark on a European tour. Two days before they were due to leave, a crucial member of their live set-up announced they couldn’t come.

The Avalanches, circa 2001 … Dexter Fabay, James De La Cruz, Robbie Chater, Tony DiBlasi, Darren Seltmann Photograph: Steve Gullick

Do you ever feel like you’re jinxed? “Nah. I mean, there always seems to be something, but I don’t feel jinxed. I feel like we’re two quite positive people, and if you just keep being positive, then whatever’s going to happen, you’re going to respond to it in the right way.”

Both of them do sound upbeat, but, as Chater points out, they have pretty good reasons. The reviews are almost uniformly ecstatic. Rehearsals for proper, full-band live shows are apparently going well. Just finishing the album would be an achievement in itself. Perhaps understandably, Chater and Di Blasi have a tendency to talk about it in mythic terms, as a voyage of discovery, a quasi-magical quest, a journey on which “all the doubt and sorrow” bonded the two of them together. Whether you buy into that or not, Wildflower sounds remarkably like a triumph. It’s beautiful, strange, intricate and completely involving, an album you can immerse yourself in. It feels oddly like quite a good advert for spending 16 years making an album.

“Well, I’m glad we did it,” says Chater, “but I’d never do it again. Not that I’m afraid of making another album, I think that fear was overcome in the making of Wildflower, we had to overcome that fear to actually get it finished. I feel, looking forward, that there’s a lot of freedom.”

There seems to be something very telling about the two old albums it most obviously references, I say. The cover looks a lot like that of Sly and the Family Stone’s There’s a Riot Goin’ on, while the aforementioned Noisy Eater is audibly a homage to Vegetables, from the Beach Boys’ legendary unfinished 1967 album Smile. Chater agrees: he starts talking about how he loves the ragged, loose sound of the former and the similarities between the methods Brian Wilson used in the mid-60s and the way the Avalanches stitch together samples.

Well, I meant more that they’re two albums shrouded in mystery and myth and the people who made them more or less lost their minds in the process. Chater laughs. “Um, that was an aspect of those records we definitely weren’t striving for. But you know, we went through a lot of stuff, and came out the other side, and we lost our minds at various stages of this. And we’re quite glad to have them back now.”