The line the guides draw
Heritage South Australia’s guidelines name the cleaner they refuse in a heading of their own: acid and the acidic cleaners, with marble or limestone singled out.
Heritage Victoria’s code is blunt where acid reaches this stone: “Avoid splashing acid on marble, glass, ceramic tiles or metal (especially lead).”
Under stronger chemicals the code says mineral acids are not recommended for marble or sandstone; elsewhere it notes that hydrochloric and sulphuric acids can cause long-term weakening and streaking in mortar, concrete and most sandstones, even after washing.
What slightly acidic water does in the ground
The Wombeyan plan follows water into the rock: as it passes through the soil it becomes slightly acidic, and in that state it dissolves the marble, slowly enlarging the cracks into passages and chambers.
The Borenore plan describes the same water finding the marble’s cracks and joints and dissolving the stone as it goes.
It matters above ground because the mineral is the same one. An acid that meets a marble surface meets calcite, the mineral the Borenore plan’s glossary describes as the commonest calcium carbonate and the main constituent of limestone.
Each state’s guide, in turn
Each heritage body writes for its own jurisdiction and names its own stone, and every answer below is stated for the state whose body gives it.
| State | What its heritage guidance says about acid on stone |
|---|---|
| SA | Acid or acidic cleaners are refused, especially on marble or limestone; household bleach is not for whitening marble, and liquid chlorine is left to conservators trained for non-calcareous stone. |
| VIC | The code asks that acid be kept off marble, glass, ceramic tiles and metal; it does not recommend mineral acids for marble or sandstone. |
| NSW | No NSW heritage rule on acid is cited here. The Wombeyan reserve’s plan of management describes slightly acidic water dissolving marble in the ground. |
Bleach, and the other strong cleaners
Household bleach is out of this work in the South Australian guidelines: not the way to whiten marble, or to take moss and lichen off stone, and no other acidic or corrosive cleaner should be used on it.
The same list allows liquid chlorine only to trained conservators, and only on stone that is not calcareous, which leaves marble and limestone out of it.
The reason sits on the same page: the wrong materials and the wrong methods can do serious damage that cannot be put right on a gravestone.
Heritage Victoria’s code lists acids, particularly hydrofluoric acid and bifluoride solutions, among the substances that can penetrate the skin even in diluted form.
Graffiti: a poultice, not a solvent
For graffiti on porous stone, the South Australian guidelines say a solvent can spread inks and dyes further in, while a poultice draws the staining out.
Two guides sit beside this one: How do heritage guides say to clean marble?, and How are stains drawn out of marble?