02/02/2026
Many people ask whether our buildings need to be cleaned. There is no simple answer to this. The Trust is fortunate to be surrounded by experts in this field, and the long-term care of Oamaru stone is still very much a learning process. In the scheme of things, Oamaru stone is a relatively new building material and is almost unique to Oamaru in this scale.
Much of the advice we receive is that our buildings do not currently need cleaning. If you take a walk around the Heritage Precinct, you will see that many of the buildings are, in fact, relatively clean. Several Trust buildings have been cleaned in the past as part of restoration projects. For example, the Criterion was cleaned in the mid-1990s, and 2 Harbour Street was cleaned in 2007 when its façade was restored, the grand facades of Tyne Street where all cleaned in the early 2000s
Oamaru stone does have some self-cleaning properties once pollutants, such as coal smoke, are removed from the environment. Over cleaning can also remove the stone’s natural protective layer, which helps to preserve it. There is a further risk that once a building is cleaned to a pristine state and ongoing cleaning continues, more and more of the stone itself can be lost.
That said, some parts of our buildings do require treatment, particularly areas affected by moss or discolouration, such as parapets and urns. The Trust will be looking at ways to fund this work and carry it out as part of routine maintenance.
The Loan and Mercantile building is an example of a building the Trust has never cleaned, following advice from our conservation architect:
“The patina of age of the Oamaru stone is an important physical attribute of the building that should not be disturbed, and no treatment is presently recommended. This includes cleaning of the building, which is not needed at present.”
At some point in the future, restoration work will be required, and to maintain visual consistency the building may need to be cleaned at that time.
Allowing buildings to age and weather at different rates adds to the overall patina of the precinct and creates a more authentic and historically appropriate appearance than having all buildings appear pristine at once.