Why high pressure can destroy sandstone — and the right way to clean natural stone

There's a common assumption that more pressure equals a better clean. On hard, modern concrete that can be roughly true. On natural stone — and sandstone in particular — high pressure is one of the fastest ways to do permanent damage.

What high pressure does to natural stone

Sandstone is soft and porous. Blasting it with a high-PSI washer doesn't just remove dirt — it removes stone. The result is etching, pitting, a furred-up surface texture, and pores opened wider so the stone soaks up the next lot of grime even faster. Once that surface layer is gone, it doesn't come back.

The same applies, to varying degrees, across the natural-stone family: travertine pits, marble and limestone etch, and softer stones lose material under pressure that concrete would shrug off.

Why sandstone is especially vulnerable

Sydney is built on sandstone, and it's our most prized heritage surface — driveways, feature walls, pool surrounds, steps and façades. It's also one of the most demanding to look after: porous, comparatively soft, and prone to salt damage and biological growth. It needs judgement, not horsepower.

The right way to clean natural stone

• Lower pressure, calibrated to the stone — soft-wash and low-pressure techniques matched to the age and condition of the surface.
• Neutral-pH cleaning — never acidic products that etch stone.
• Targeted biological treatment — moss, algae and lichen treated chemically rather than blasted off.
• Breathable sealing — a penetrating sealer that lets the stone breathe while blocking water and salt, rather than a film that traps moisture underneath.

Why "cheap and fast" costs more later

A contractor who turns up with a pressure washer and one technique for every surface will get sandstone looking clean for a week — and leave it permanently rougher and quicker to re-soil. Restoring stone that's been over-blasted is far more expensive than cleaning it correctly the first time, and some damage simply can't be undone.

Stones that need specialist care

Sandstone, travertine, limestone and marble all reward a careful, stone-specific approach. If a quote doesn't mention matching the method to your surface, that's worth asking about before any water touches the stone.