Soft Washing: The Complete UK Guide

How does soft washing actually work?

Soft washing uses a biocide solution, typically a diluted sodium hypochlorite-based product or similar, applied at low pressure to kill moss, algae, lichen and fungal growth at the root, rather than physically blasting it off the surface. The solution is left to dwell for a period, usually twenty minutes to an hour depending on the product and severity of growth, giving it time to penetrate and kill the organism fully.

After dwelling, the surface is rinsed at low pressure, which removes the dead growth along with the residue. Because the biological growth is killed rather than just removed, soft washing typically gives results that last considerably longer than pressure washing alone, since regrowth has to start from scratch rather than from surviving root systems left behind by physical scraping or blasting.

Which surfaces suit soft washing?

Roof tiles, render of all types including modern K-rend and silicone systems, pebbledash, natural stone, and uPVC roofline all suit soft washing well, particularly where the problem is biological growth like moss, algae or lichen rather than simple ingrained dirt. It's the recommended approach on anything soft, porous, or where high pressure risks forcing water behind the surface.

Soft washing is less necessary, though still an option, on surfaces like tarmac and concrete where the growth is more surface-level and physically robust enough to tolerate higher pressure without damage, though a soft wash approach can still give a longer-lasting result even here.

Safety considerations with biocide treatments

Biocide products used in soft washing are effective but need to be handled and applied correctly, including protecting nearby plants, covering ponds or water features, and being mindful of run-off near drains. A biocide-trained professional understands correct dilution ratios, appropriate dwell times for different surfaces, and how to minimise environmental impact during and after application, which matters both for effectiveness and for avoiding harm to gardens or watercourses.

This is one area where checking a contractor's training genuinely matters, since incorrect biocide use can damage plants, discolour surfaces, or simply be less effective, wasting money on a treatment that doesn't actually solve the problem.

What soft washing typically costs

Pricing varies by the surface and area being treated, but as a guide, a full render soft wash on a semi-detached house typically runs from around £300 to £600, while roof soft washing sits closer to £400 to £900 depending on size and moss coverage. Combining multiple surfaces, such as roof, render and roofline, on the same visit is often more cost-effective than booking each separately, since setup and biocide preparation overlap.