Science comes to the rescue of Sydney's sandstone

Science is coming to the rescue of Sydney's historic sandstone buildings with a first-ever study by a chemist at the University of Technology, Sydney into the forces chipping away at the city's heritage.

In the past year PhD student Kin Friolo has pinned down the reasons building blocks cut from Sydney's distinctive yellow sandstone will first discolour and then slowly disintegrate, eventually requiring major restoration work.

Now Ms Friolo is working on a treatment that aims to arrest degradation, repair damage and head off the need to replace stone, especially when blocks from the original source can no longer be obtained.

"The previously available research from Europe showed that the major problem for sandstone buildings is the freezing of water absorbed by the stone," Ms Friolo said. "Of course, that's not relevant to Sydney. In Australia, by contrast, the enemies are high temperatures, strong ultra violet light and, in coastal areas, salt.

"The damage to Sydney sandstone buildings is due to the breakdown of the clay that holds the sand grains together and is related to the oxidation of iron in the stone. Over time oxidation causes the surface of the stone to turn orange, but more importantly, the outer layer becomes very brittle and can easily be broken off. The next layer exposed is affected in the same way and the block will eventually crumble away from the outside in."

Armed with her detailed chemical profile of Sydney sandstone Ms Friolo is devising a compound, tailored to the Australian climate, that will fill and bind oxidised sandstone surfaces and hopefully also reverse discolouration.

"The goal is to reintroduce a binding agent, based on the natural clay, back into the stone, but chemically modified so that further oxidation can be prevented. The binding agent will both penetrate the outer layer of stone and fill gaps. It will also need to be permeable like the stone so that moisture is not trapped under the repair.

"In Europe the use of some waterproof polymers to coat sandstone surfaces has actually caused greater damage."

The NSW Department of Public Works and Services and Gosford Quarries have expressed interest in Ms Friolo's work.

Item provided courtesy of UTS