Soft washing explained
Soft washing is low-pressure application of a biocide solution that kills algae, lichen and moss at the root instead of blasting the surface. It is the correct method for render, roofs and cladding, and its residual effect keeps killing spores for months, so results last years rather than a season.
Last updated: August 2026.
The problem with pressure
A pressure washer cleans by force: it strips the visible growth off a surface and leaves it looking clean. What it leaves behind is the root system: algae, lichen and moss anchor into the pores of render, tile and cladding, and cutting the top off is pruning, not killing. The regrowth comes back denser, and on a damp Teesside wall it can show within months. Worse, pressure on the wrong surface does permanent damage: render faces stripped, roof tile granules scoured off, water forced behind cladding and through seals.
How soft washing works
Soft washing reverses the logic: chemistry cleans, water only rinses. A biocide solution is applied at roughly garden-hose pressure, given time to soak into the surface and kill the growth at the root, then gently rinsed. Because the treatment is biocidal rather than mechanical, it reaches into the pores where growth anchors. And because modern biocides are residual, they keep killing the spores that land on the surface for months afterwards, which is why a soft-washed wall stays clean for two to four years while a pressure-washed one regrows in a season.
Which surfaces need it
Render (k-render, painted render, pebbledash): always soft wash; pressure strips the coloured face. Roofs: scrape the moss, then biocide; never pressure wash tiles. Cladding and uPVC: soft wash or pure-water pole; pressure lifts laps and blows seals. Brick and stone: soft wash, especially on period lime pointing. Hard ground surfaces like block paving and concrete are the exception: they take pressure well, which is a different trade's job.
The red and green you are actually looking at
The growths on Teesside walls have names and habits. Green algae colonises shaded, damp walls: north and east elevations, tree cover, anywhere slow to dry. Red algae streaks modern k-render with pink-red runs, common on the newer estates. Black spot lichen dots render and paving and resists everything except dedicated treatment. Moss anchors on roofs and holds moisture against tiles. Each responds to biocide; none responds permanently to force.
Is it safe?
Done professionally, yes. Biocides are applied diluted, at low pressure, with planting wetted and covered first and everything rinsed afterwards. The products break down quickly in the environment. The risk profile sits with the alternative: high pressure near window seals, roof laps and render faces is where the expensive accidents live.