Follow the yellowblock road

Some of Sydney’s beloved buildings and landmarks are constructed from ‘yellow gold’. But with sandstone stockpiles running low, the government and property industry are partnering to uncover this underground treasure.

From St Mary’s cathedral to the Queen Victoria Building, and from Town Hall to Darlinghurst Jail – many of Sydney’s early buildings were constructed from the hard-as-nails sandstone that gave the city its distinctive architectural style.

But our stockpiles of “freestone” are in short supply, demanding new approaches to this ancient material.

From the colony’s earliest days, settlers found sandstone in such plentiful supply that they were profligate with its use.

As late as 1915 it was still called freestone. Convicts, employed to tunnel the Argyle Cut at The Rocks, dumped their diggings in the mangrove swamps that would later become Circular Quay. Millions of cubic metres were cut from Sydney’s Cockatoo Island to create a dry dock. Families favoured sandstone over hardwood huts for decades.

By the 1850s, at least 22 quarrymen worked the Pyrmont quarries. Overseen by Charles Saunders, the quarries were known locally as Paradise, Purgatory and Hellhole – the names relating to the degree of difficulty in working with the stone.

By the middle of the 20th century, though, as sandstone made way for concrete and steel, the stone had fallen out of favour and was the mere bedrock of suburban gardens. Sandstone buildings had lost their charm, and even that grand old dame, the Queen Victoria Building, faced demolition.


Striking gold

Today, a small but highly-skilled team of stonemasons, under the watchful eye of the Minister for Finance, Service and Property’s Stonework Program, repair and restore some of NSW’s 800-plus sandstone heritage-listed sites.

Yellowblock is now a “rare and sought after material”, says Troy Vanderplas, director of heritage stoneworks from the NSW Department of Finance, Services and Innovation.

“Due to the diminished stockpile of sandstone over the last 16 years, the government’s best option to source yellowblock sandstone that matches the colour, quality and performance of the original stone, is from redevelopment sites surrounding the original quarry locations,” Vanderplas explains.

The NSW Government has worked closely with the City of Sydney and other councils to “core test” redevelopment sites, particularly near former historical quarries, and to ensure “development application conditions require the option of harvesting sandstone,” Vanderplas adds.

One of the greatest quarries of sandstone in recent years was unearthed by Lendlease during the development of the Barangaroo Reserve.

Along the headland, which was one of Sydney’s oldest industrial sites, lay 1.4 kilometres of scarred foreshore that needed to be painstakingly reshaped and restored.

“That 1.4 kilometre stretch of shoreline was considered the missing piece linking Pyrmont to the Sydney Opera House – and it needed to be recreated with sandstone,” says Kieron Little, Lendlease Engineering’s general manager for health and safety who was the project director of Barangaroo Reserve.

Lendlease extracted an eye-watering 35,000 cubic metres – yielding roughly 10,000 blocks – from Barangaroo itself. Ninety-three per cent of the blocks were extracted from beneath what is now the Cutaway, a cultural space beneath the headland.


Everything old is new again

Little and his team looked back at lessons gleaned from Saunders and other quarry masters and adopted similar techniques, albeit with the help of modern machinery.

“We did a lot of research to understand how Sydney sandstone behaves,” Little explains, pointing to Lendlease’s decision to establish the excavation site along the 22-degree faultline that runs through Sydney.

“This was a technique they used 200 years ago when they didn’t have heavy machinery – but it meant we were able to peel the sandstone blocks off neatly.”

The result was a “pleasing and natural look” with as little waste as possible.

The natural methods are jaw-droppingly efficient in comparison to the old-fashioned approach of water and wooden wedges. Lendlease used a triple-blade saw, each three metres in diameter, to cut the sandstone.

Each slab of sandstone had to be carefully graded, because the best blocks had to withstand tidal influences twice a day. Those deemed best quality, with no clay content, were chosen for the water’s edge, while the outcrop blocks could be rougher in finish and less durable, “but they still needed to have the appearance of being part of the headland”. Those that didn’t make the grade were used for road base and drainage.

The environmental benefits of Lendlease’s approach are clear – reusing a natural material close to the source meant that “35,000 cub metres of sandstone didn’t have to be put on the back of a truck and sent out to landfill, with all the greenhouse gas emissions that entails,” Little says.

But making the most of this precious natural resource requires a partnership approach.

“The headland park is a great example of where government, the client and the developer got together to understand key outputs for the project, and to create something that benefits everyone,” Little explains.

“You can achieve incredible outcomes if the project is well-planned and considered a partnership from the beginning. But you need to plan long before you get to site. You can’t think about quarrying the sandstone once there’s a big hole in the ground.”