Every stone sculptor who places work outdoors enters into a long negotiation with the weather. No matter how carefully you select your material and finish your surfaces, the moment a sculpture goes outside it begins to change. Understanding how and why this happens is essential for creating work that ages well rather than simply deteriorating.

I have had pieces installed across south-eastern Australia — from coastal Mornington Peninsula to inland regional Victoria — and each environment presents different challenges.

Water: The Primary Agent

Water is responsible for more stone deterioration than any other single factor.

Absorption and evaporation cycles. All natural stone is porous to some degree. Each wet-dry cycle draws dissolved minerals toward the surface, creating whitish salt deposits called efflorescence. In porous stones like sandstone, these cycles cause surface flaking as salts crystallise just below the surface and push off thin layers of material.

Freeze-thaw damage. While less common in coastal Australia than in Europe, frost affects stone in elevated and inland areas. Melbourne’s outer suburbs regularly experience winter frosts. Water in cracks expands as it freezes, widening those cracks each season. Granite resists this well. Sandstone and limestone are more vulnerable.

Running water erosion. Sculptures where rainwater consistently flows over the same path will develop channels over decades. Designing drainage into the base and avoiding flat horizontal surfaces helps considerably.

Heat and Thermal Cycling

Australian summers put significant thermal stress on outdoor stone. A dark granite sculpture in full sun in Melbourne can reach surface temperatures above 60 degrees Celsius, then cool to 15 degrees overnight. This daily expansion and contraction creates micro-fractures over time.

The effect is more pronounced in stones with mixed mineral compositions. Granite contains quartz, feldspar, and mica, each expanding at different rates when heated. Over decades, this differential expansion loosens the grain structure at the surface, causing granular disintegration.

Lighter-coloured stones absorb less heat and experience less thermal stress — one practical reason why white marble has long been preferred for outdoor sculpture.

Salt and Coastal Exposure

For anyone placing sculpture near the Australian coast, salt is the dominant concern. Airborne salt spray can travel several kilometres inland. Salt crystals growing in pores and cracks exert enormous pressure, and the process repeats with every wet-dry cycle.

Stone selection for coastal sites:

• Granite is the best choice. Low porosity and hard mineral composition resist salt penetration.
• Dense basalt performs similarly well.
• Marble is moderate — porosity allows some salt penetration.
• Sandstone and limestone are poor choices for exposed coastal locations.

If you must use softer stone near the coast, a penetrating silane or siloxane sealer can slow salt ingress. These need reapplication every five to ten years.

Biological Growth

Australia’s warm, humid conditions promote biological colonisation of stone surfaces. Lichen, moss, algae, and even higher plants will establish on outdoor sculpture over time.

This is not always a problem. Many sculptors consider biological growth part of the stone’s life outdoors. A marble figure with a fine patina of grey-green lichen can look more beautiful than a freshly cleaned one.

However, plant roots penetrate cracks, some lichens produce acids that dissolve stone, and black algae can stain permanently. Gentle cleaning with a soft brush and water is usually sufficient. Avoid pressure washers — they strip the surface and force water deep into the material.

Planning for Durability

When I design a piece for outdoor installation, I consider site conditions from the beginning:

• Choosing the right stone for the location. I would never put sandstone on an exposed coastal headland.
• Designing drainage. Incorporating subtle slopes and raising the base off the ground to prevent moisture wicking.
• Specifying an appropriate base. A concrete or stone plinth with a damp-proof course prevents moisture staining.
• Documenting care instructions. Clients and councils receive written guidance on cleaning and maintenance. AI consultants in Melbourne have been exploring ways to use digital tools for long-term asset management of public art — an approach that could help preserve outdoor collections more systematically.

Working With Time

All outdoor stone sculpture is temporary on a long enough timeline. Even the pyramids are slowly eroding. The sculptor’s job is not to defeat time but to understand it — to choose materials and forms that will age gracefully.

There is a word in Japanese — sabi — that describes the beauty of things worn by time. A stone sculpture that has weathered forty Australian summers and winters has a depth that no freshly carved piece can match. Designing for that process, rather than against it, is one of the most rewarding aspects of working with stone outdoors.