They look similar from the street but achieve completely different results. One kills the growth. The other blasts the surface and leaves the roots behind. Understanding the difference could save you money and protect your property.
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The difference between soft washing and pressure washing is not just about the amount of pressure — it's a fundamentally different approach to the problem. Pressure washing uses high-pressure water (typically 2,000 to 4,000psi) to physically blast contamination off surfaces. Soft washing uses a chemical biocidal solution applied at very low pressure (typically 50 to 150psi) to kill biological growth at root level, followed by a low-pressure rinse. The results look similar immediately after both methods — but the difference becomes apparent over the following months. Pressure-washed roofs typically show regrowth within 6 to 12 months. Soft-washed roofs stay clean for 12 to 24 months, because the growth was killed rather than just displaced.
Pressure washing is genuinely effective for certain applications: cleaning concrete driveways and paths (where the surface can withstand high pressure and the contamination is primarily surface-level dirt), cleaning vehicles and boats, and removing loose dirt from surfaces that don't support biological growth. For these applications, high pressure is appropriate and effective.
For roofs, rendered walls, weatherboard, fibro, colorbond and other building materials, pressure washing is either ineffective, damaging or both. It physically strips tile surfaces, cracks mortar, lifts render, voids colorbond warranties and forces water into wall cavities. More fundamentally, pressure washing doesn't kill biological growth — it displaces it. Algae, lichen and moss roots survive and regrowth occurs rapidly.
Soft washing is specifically developed for biological growth on building surfaces. The chemical solution (typically sodium hypochlorite with surfactants) kills mould, algae, lichen and moss at root level — including the spores that cause regrowth. The results last 12 to 24 months and there's no mechanical force on the surface. It's the correct method for roofs, house washing, heritage homes and any surface where pressure washing carries damage risk.
For roofs — always soft wash. For house exteriors — soft wash. For driveways and concrete paths — pressure cleaning is typically appropriate. For renders, weatherboard, fibro, colorbond and heritage surfaces — always soft wash. For heavily contaminated driveways with deep staining — a combination approach may be used.
Yes — unambiguously. Soft washing kills biological growth at the root and doesn't damage roofing materials. Pressure washing displaces growth without killing it (rapid regrowth), and can damage tiles, strip colorbond coatings, damage ridge cap mortar and force water under tiles.
Yes, for most exterior surfaces. Rendered walls, weatherboard, fibro and colorbond all require the gentle approach of soft washing. High-pressure washing on these surfaces risks surface damage and forces water behind cladding.
Yes — a biocidal solution, typically sodium hypochlorite with surfactants. These are professional grade products that are safe on building materials and safe for gardens and pets after thorough rinsing.
Typically 3 to 4 times longer. Pressure-washed roofs show regrowth within 6 to 12 months. Soft-washed roofs stay clean for 12 to 24 months because the growth organism is killed rather than displaced.
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