Cleaning Sandstone Without Damaging the Surface

Sandstone is everywhere on Sydney's Northern Beaches — feature walls, steps, pool surrounds, pathways, entire front façades. It ages beautifully. It also stains, grows lichen and, if cleaned carelessly, scars permanently. The biggest mistake we see is someone hitting it with a high-pressure wand at close range. The face pits, the detail blurs, and there's no fixing it.

Why sandstone is different

Sandstone is soft, porous and mineral-bonded. Aggressive pressure literally blasts grains off the surface. Aggressive acids etch it and open the pores so it picks up dirt faster than before. The right approach respects both of those things: gentle mechanical force, and chemistry that does the work without damaging the stone.

The method that works

• Pre-rinse at low pressure to flush loose dirt and debris.
• Apply a sandstone-safe cleaner or a diluted soft-wash mix suited to the organic growth present.
• Let it dwell — don't scrub while it's drying.
• Agitate with a soft or medium bristle brush, never a wire brush.
• Rinse at low pressure from a sensible distance — not the 0-degree tip, not up close.

What actually kills lichen and black spots

Those crusty white or grey patches are lichen, and the dark mottling is a mix of algae and mould. Both are biological. Neither comes off with water alone, no matter how much pressure you use. They need the right chemistry — usually a sodium-hypochlorite-based soft wash at a controlled dilution — applied, dwelled, and rinsed. Done properly, it's the method behind every good sandstone cleaning job.

What not to do

• Don't use muriatic acid or strong HCl-based cleaners — they etch the face.
• Don't use wire brushes, grinding discs or scourers.
• Don't run a turbo/rotary tip at close range on the stone.
• Don't seal sandstone while it's still damp or contaminated — you'll lock the problem in.

Once it's clean

Sealing clean, dry sandstone with a breathable penetrating sealer slows down future staining and organic growth without changing the colour. It's optional, but on high-traffic paths and pool surrounds it pays for itself in how long the clean lasts.