Two mine shafts stood in the way of a gallery extension. It took 15,000 cubic metres of grout to sort out

Above two deep coal mine shafts stands the most significant transformation of the NSW regional art landscape in more than a decade. After a four-year closure, Newcastle Art Gallery officially reopens this Saturday, its $48 million expansion more than doubling its footprint to house a world-class $145 million collection previously hidden from view.

The new wing, designed by Clare Design with Smith & Tzannes and Arup, is as much an engineering feat as a cultural one.

To stabilise the “Swiss cheese” of 19th-century mine workings beneath the site, engineers pumped 15,000 cubic metres of grout — roughly six Olympic-sized swimming pools of concrete —through 100 specialised boreholes.

This voluminous slurry of cement and fly ash was essential to prevent subsidence. And the year-long process also served as an archaeological dig, uncovering artefacts from old workers’ cottages and a cordial factory.

“We’ve got mine shafts right under our city, a myriad of subterranean pathways” says director Lauretta Morton. “We had the big tanks out the back; trucks and pumps going on behind the scaffold, and people were seeing nothing being built and, yet, it was all happening underground.”

Two earlier expansion plans failed amid funding shortfalls and political squabbles. One former lord mayor described the gallery plans as a waste of time. Success was finally achieved through a coalition of support: $25 million from the City of Newcastle, $13 million from the Gallery Foundation, and $10 million in grants.

“I used to stalk previous arts ministers,” Morton says. “I used to find out where they were going to be and I’d drive down the highway and turn up, and ask, ‘when is the money going to come [north of] the Hawkesbury’.”

The new extension increases the number of gallery spaces from five to 13. The additional 1600 square metres of exhibition space makes Newcastle the largest public gallery in NSW outside Sydney.

The former courtyard has been converted into a glass-walled atrium featuring a “floating” staircase– a suspended, white geometric structure designed to bridge the original 1977 brutalist building and the airy extension. First Nations culture takes centre stage in the atrium with Megan Cope’s monumental installation, Kinyingarra Guwinyanba (Off Country).

Nick Mitzevich, a former director now leading the National Gallery of Australia, recalls the gallery had one of the best regional collections in the country, but nowhere to show it off.

“It was literally bursting at the seams,” he says. “The gallery footprint far exceeded visitor numbers, and it was always congested. It’s now a facility of great scale and amenity with a standalone bookshop, and restaurant and fulfils the full gamut of research, schools and exhibition programs.”

Says Morton: “This is the first time our collection, anywhere in the gallery, has been on permanent display because before now we didn’t have the space, and we had to constantly do a 12-week cycle of exhibitions.

“Just in this gallery space, we’ve got some Australian hits. Williams, Boyd, Gascoigne, Hinder, Olsen, Blackman, Smart, Gleeson, and Tucker,” Morton says. “We have the most significant collection outside the state and national galleries, including the largest collection of avant-garde Sodeisha ceramics outside of Japan.”

Local legends also feature prominently. William Dobell grew up two streets away, and Margaret Olley was once a landlord to the nearby terraces on Church Street; a new gallery space has been named in her honour.

The reopening is anchored by a significant gift from philanthropists Simon and Catriona Mordant. Their donation of 25 contemporary works – thought to be valued at about $1 million – includes pieces by Janet Laurence, Maria Fernanda Cardoso, and Novacastrian artist Jamie North. It is the largest number of artworks the philanthropists have ever gifted a single institution.

Mordant says Newcastle and its energetic director were worthy recipients of artworks drawn from the couple’s massive collection built over 40 years. “We believe art should be seen and enjoyed by the widest possible audience.”

The Mordant gifts join John Olsen’s The Sea Sun of 5 Bells, the only one of his ceiling paintings on permanent display in an Australian gallery. Also out from storage is Brett Whiteley’s Wynne Prize winner, Summer at Carcoar, a departure from Whiteley’s signature aquamarine blue canvases of Sydney.

The gallery owns three of four known works by the convict painter Joseph Lycett, hung between Abdul-Rahman Abdullah’s carved draped white covered work, a commentary on the “lie” of Lycett’s peaceful pastoral scenes.

Upcoming highlights include the first major Australian survey of Angela Tiatia in September, followed by a solo exhibition by painter Anh Do in November, featuring his celebrity portraits and new landscapes.

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