Walk through any residential suburb in Sydney or Newcastle and you’ll see roofs in various states — some dark and covered in moss, others visibly blotchy with lichen and algae staining. The temptation is to blast it off with a pressure washer and be done with it.

But roofing professionals and insurers agree: pressure washing is the wrong tool for most roof types. Here’s why — and what soft washing does instead.

The Problem with Pressure Washing Roofs

High-pressure water (anything above 500 PSI) applied to roof surfaces causes several specific types of damage:

Concrete tiles

Concrete roof tiles have a protective granule coating that provides colour, UV resistance, and weather protection. High-pressure washing strips these granules from the surface, leaving the concrete exposed. Exposed concrete tiles absorb more water, crack under freeze-thaw cycles, and age significantly faster.

Terracotta tiles

Terracotta is brittle. High-pressure water can crack individual tiles, and the force dislodges the mortar at ridges and valleys — the critical waterproofing points on your roof. Replacing cracked terracotta tiles is expensive, and re-bedding ridge mortar is more expensive still.

Colorbond and metal roofing

Metal roofing is more pressure-tolerant than tiles, but high-pressure cleaning can still force water under laps and flashings, and damage the protective paint coating — particularly on older Colorbond. Most metal roof warranties specify low-pressure cleaning only.

It doesn’t solve the problem

Perhaps most importantly, pressure washing removes the visible growth — the moss, lichen and algae — but leaves the spores and root structures embedded in the surface. Regrowth typically begins within 6–12 months, often faster than before because the surface has been roughened by the pressure.

What Soft Washing Does Differently

Soft washing applies a biodegradable biocide solution at low pressure — typically under 500 PSI, no more forceful than a garden hose. The cleaning chemistry penetrates the cell walls of moss, lichen, algae and mould, killing the organisms at the root.

Over the following weeks and months, rainfall and natural weathering wash away the dead growth. The surface isn’t just cleaned — it’s sanitised, and the treatment continues working, typically preventing regrowth for 2–4 years depending on tree canopy, humidity and environment.

For concrete tiles, soft washing preserves the protective granule coating. For terracotta, there’s no force that could crack a tile or disturb mortar. For Colorbond, the paint coating remains fully intact.

What About the Gutters?

A soft wash roof treatment pairs naturally with a gutter clean. As the dead growth washes down over subsequent weeks, gutters fill with debris. We recommend combining a soft wash treatment with gutter clearing at the same time — and then a follow-up gutter check 8–12 weeks later if the roof had heavy coverage.

How to Tell If Your Roof Needs Treatment

Look for:

• Black or dark streaking — algae and cyanobacteria
• Green patches — moss or lichen, particularly in shaded areas
• Orange or rust-coloured staining — often lichen on terracotta
• General darkening of the roof colour — biological film accumulation

Left untreated, biological growth retains moisture, adds weight to the roof, and accelerates tile degradation. A roof that looks dirty is also reducing your home’s kerb appeal and, potentially, its value.

Book a Roof Soft Wash

DSK Cleaning uses professional-grade soft wash equipment and bio-safe cleaning solutions across Sydney, Central Coast, Lake Macquarie and Newcastle. All work is fully insured and we carry $20M public liability cover.

Call 0423 668 766 or get a free quote.