TITLE TK Barangaroo Sandstone Story

The vast array of stonework that defines Barangaroo Reserve was pulled directly from beneath a portion of the site. Its placement involved a combination of precision, intuition, and obsessiveness, as David Walker, FASLA, a partner at PWP Landscape Architecture, explains here.

The 37,000 cubic meters of Sydney’s iconic Hawkesbury sandstone that created the new foreshore was excavated from massive slabs, cut with 3-meter diameter blades to the size specifications defined by a 3D Revit model. All of the blocks were then bar-coded and GPS-located into their specific foreshore placements. The block sizes measure about 1.2 meters width by about 5 meters in length.

The quality of the sandstone extracted on site exceeds the required strength, and they are embedded with a huge variety of characteristic markings, such as veins of pure iron deposits, prehistoric shell, and other foreign stone deposits. This was a welcome surprise. When the first excavated blocks were inspected, we knew right away that we had something unique.   

The variation in coloration and unique markings of the sandstone is the natural variation that occurs between veins located on site. These qualities would not have been possible if a commercial supplier simply purchased the blocks. Commercial suppliers generally regard these irregular characteristics of stone as undesirable and they discard them—they are trained to deliver consistency. 

During the almost two-year process of extracting and placing the stone, there was an ongoing discussion during each of my construction visits, between PWP and the chief stonemason, Troy Stratti, concerning the relative distribution of block colors. We encouraged Troy to highlight the unique vein markings and left it up to his discretion. After hundreds of discussions, we made a formal specification regarding the color variation in the sandstone. As the stones were cut out of the ground, they were categorized into three color ranges; white, yellow, and red. The distribution of these colors was not to allow too many white stones to be placed next to each other, because they stood out the most, but rather to blend them into the other colors.  During the months of installation, we had the opportunity to observe that the color variation was not important within the tidal zone, where the stones would become dark and covered with algae. So the discussion of equal color distribution became focused closer to the foreshore promenade, which is where it  would be visible by the majority of people in the park. The stones were cut for specific locations in the plan. Four sides were saw-cut, and the top and the bottom were natural split surfaces.  The only discretion left to the equipment operator was which split surface would face upward, and the stone direction could be flipped. Limiting the aesthetic decisions by the equipment operators was important for the schedule to proceed quickly.

After about a year of working with Troy, he Knew very well what our design intentions were, and this is when our focus shifted to stone selection for the most careful part of the design, which includes Nawi Cove, the grand staircases, and the 1836 wall (a whole story in itself). The 1836 Wall was a unique effort because we needed to create a consistent color and finish for more than a kilometer.  This is the only stone on the project acquired off site from a single quarry in Bundanoon, located about an hour south of Sydney.  Even with a large sole source for the stone at Bundanoon, the sheer quantity of consistent character stone required began to run out and we needed to strategize how to complete the last ten percent with a consistent color and finish.

Troy and I spent days on each of my monthly site visits  walking the site at all possible hours of the day including sunrise, sunset, nighttime, and in rainy weather, to understand how the stone quality was perceived differently depending on the quality of light. These in-depth (bordering on obsessive) observations and discussions on our walks culminated when Troy and I worked with his equipment operators to direct placement of the sandstone rock outcroppings, which became perhaps the most challenging effort at the end of the construction schedule. The rock outcroppings could not be specified, and required the two of us to work out the criteria while moving them into place.

Troy and I had gradually developed full aesthetic control of the stone work for Barangaroo, because it was simply too hard for anyone else to take responsibility for the aesthetic outcome over the entire site. It was worked out by trial and error in the field. We corrected our mistakes as we progressed, and allowed ourselves the time to reflect and brainstorm about the possible solutions for constructability and the best aesthetic outcomes.  

The sandstone story at Barangaroo is large, because it follows the sandstone tradition of Sydney. The tradition was passed down to Troy Stratti, whose company, which he started with his father, Sam Stratti, invented the saw blades to cut the stone. They have the deep understanding of the extraction and fabrication process in Sydney. Troy once said to me that he felt that he had been preparing his entire career for the opportunity and challenge of Barangaroo Reserve.

--David Walker, FASLA