Short answer: a biocide treatment is a solution applied to a patio, drive or deck that kills moss, algae and lichen down to the roots, so the surface stays clean for far longer after a wash. It works through dwell time rather than force, and it is what stops green growth reappearing within weeks of a clean.
Moss, algae and lichen are living organisms with root structures that sit inside the pores and joints of a surface. Pressure shears the visible top layer off. It doesn't kill what's below it. That's the difference between a drive that looks clean for a season and one that still looks clean the following spring.
How it works in practice
- The surface is pre-wetted or cleaned depending on how thick the growth is.
- A biocide is applied evenly and left to dwell — this takes time, not force.
- The organism dies back over the following days and weathers off, or is rinsed as part of the clean.
- On heavy lichen, a second application is sometimes needed rather than a heavier wash.
Where it makes the biggest difference
- North-facing patios and shaded side returns that never fully dry out.
- Under trees and hedges, where leaf litter feeds growth every autumn.
- Porous stone such as Indian sandstone, where black spot roots deeply.
- Anywhere water sits because of poor falls or a blocked gully.
How long it holds
Realistically, a treated and re-sanded drive holds its appearance for a couple of years before the next treatment, and a shaded patio somewhat less. A soft-wash plus biocide treatment on Yorkshire stone typically stays clean 12–24 months in shaded gardens. Sun, drainage, overhanging planting and how often the surface is swept all move that.
We'd rather give you that range than promise a number we can't stand behind.
Biocide before or after cleaning?
Both approaches are used. On light growth the surface is usually cleaned first and the biocide applied afterwards, so it reaches the roots and pores directly. On very heavy moss or lichen a pre-treatment softens and kills growth ahead of the clean, and a follow-up application finishes the job.
Either way, the treated surface keeps improving for days or weeks afterwards as dead growth weathers away. Black spot lichen in particular fades gradually rather than disappearing on the day, which is normal.
Biocide treatment vs bleach and household products
- Bleach whitens growth on the surface but doesn't reliably kill the roots, so it greens up again.
- It can discolour natural stone and coloured concrete, and it is harsh on lawns and borders the run-off reaches.
- Washing-up liquid and vinegar remedies have little lasting effect on established lichen.
- A purpose-made biocide is applied at the correct dilution and left to work, which is why the result lasts.
Getting the most from a treatment
A treatment buys you time, and a few simple habits decide how much of it you keep. None of this replaces the biocide — it just delays the regrowth, and it's why two surfaces treated the same day can look very different a year later.
- Sweep regularly. Leaf litter and debris hold moisture and feed the next round of growth, so a swept patio stays clean noticeably longer.
- Keep water moving. A blocked gully or a low spot where water sits greens up first — the same surface with decent drainage lasts far longer.
- Let in light and air where you can. Shade is why north-facing patios and side returns struggle, so trimming overhanging planting stretches the result.
- On block paving, keep the joints full of kiln-dried sand after a clean. Tight, filled joints leave less room for new growth to establish.