Soft washing does genuinely kill algae, moss and mould spores, not just wash away visible dirt, because the chemical treatment used is specifically formulated as a biocide or algaecide that acts on the organism itself, including spores lodged in pores and crevices a purely mechanical clean would miss. This is the key distinction between soft washing and simply hosing or pressure washing a surface clean.
Understanding that difference matters because it explains why soft washing tends to last longer and why it's the recommended method for organic growth specifically, rather than general dirt and grime.
Cleaning versus sanitising: the actual difference
Cleaning removes visible dirt, dust and surface grime, restoring appearance without necessarily addressing what caused any organic growth in the first place. Sanitising, which is what soft washing's chemical treatment does, kills the living organism itself, algae cells, moss roots, mould and mildew spores, at a biological level, addressing the actual cause rather than just the visible symptom.
A pressure wash alone can make a surface look clean immediately by physically blasting growth away, but it leaves behind microscopic spores in cracks, pores and crevices that the water jet couldn't fully dislodge, and those spores simply regrow given time and moisture.
Why this matters for porous surfaces especially
Render, roof tiles, pebbledash and other porous or textured surfaces have countless tiny crevices where spores can lodge well below what a pressure jet can physically reach and dislodge, which is exactly why sanitising treatment matters more on these surfaces than on smooth, non-porous ones. The biocide solution penetrates into these spaces in a way mechanical force alone can't replicate.
This is also why soft washing typically outlasts pressure washing on the same surface by a meaningful margin, often a year or more, because it's tackling spores that would otherwise have survived a purely mechanical clean and regrown within months.
What soft washing doesn't do
Soft washing isn't a sterilisation process that leaves a surface permanently spore-free; new spores from the surrounding environment, carried by wind, rain, birds, will inevitably settle on any exterior surface again over time. What it does is remove the existing colony and its spores at the point of treatment and, with residual biocide products, leave behind some ongoing inhibition against new growth establishing quickly.
It's a genuinely more thorough treatment than cleaning alone, but it's still a maintenance measure that needs repeating periodically, not a permanent, one-time fix.
How to tell if a company is actually soft washing or just calling pressure washing by a different name
Genuine soft washing uses low pressure, similar to a garden hose in force, with the actual cleaning work done by the chemical treatment dwell time rather than water force, and it's a two-stage process: apply, let it dwell for a set period, then rinse. If a company describes their service as soft washing but is visibly using a pressure washer at anything close to driveway-cleaning force, that's a mismatch worth questioning, since it suggests marketing language rather than the actual low-pressure, chemical-led method.
Asking what product they use and how long it's left to dwell before rinsing is a fair way to check whether a contractor genuinely understands and practises soft washing, rather than just using the term because it sounds more premium than pressure washing.
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