What the guides say about coatings on old stone
The South Australian guidelines are plain: a protective coating has no place on old stone or masonry.
Where original paint survives on a monument, they treat it as evidence and ask that cleaning leave it in place.
Behind that sits the stone’s own history. Heritage South Australia’s note calls a patina evidence that a building has survived through time, part of its cultural significance, not to be taken off unless it is demonstrably harming the masonry.
The same note asks that patina and injurious grime be told apart, and says aggressive cleaning that strips the case-hardening leaves the stone more open to decay.
Where a coating was there before
New South Wales writes the narrowest version of the same thought. Under its standard exemptions, protective coatings may only be applied to surfaces which have previously had these coatings.
The exemption also holds existing finishes in place rather than modern alternatives, and asks that surface patina important to the item’s heritage significance be preserved during maintenance and cleaning.
Its scope: items listed on the State Heritage Register, or subject to an interim heritage order.
Painting is treated the same way. The exemption does not allow painting previously unpainted significant fabric, naming face brickwork, stone, concrete and metal among it.
Why a benchtop is not answered here
None of the heritage guides cited on this page gives guidance for sealing a kitchen or bathroom surface at home.
What they cover is old and heritage stone: the South Australian guidelines write for old stone, masonry and monuments, and New South Wales writes for items on its State Heritage Register.
What the guides leave open
South Australia’s guide to developing State Heritage Places gives this principle: a change should not diminish, destroy or conceal what makes the place significant, and one that can be undone without leaving damage is generally acceptable.
Where a decision has to be made, that guide sends owners to a suitably experienced heritage consultant, or to a heritage adviser through the local council, before an application is lodged.
New South Wales puts the same duty differently: any activity done under an exemption must be carried out by qualified people with the right knowledge, skills and experience.
Where this question goes next
Two guides sit beside this one: How are stains drawn out of marble?, and How do heritage guides say to clean marble?