How Long Does Biocide Treatment Last?

One of the most common questions after a clean is: "How long before it all comes back?" The honest answer depends on the surface, the exposure, and whether we used biocide — which we always do.

What biocide actually is

Biocide is a broad term for a chemical that kills biological growth — algae, moss, lichen, and mould. The products we use are professional-grade, formulated specifically for exterior stone, tile, and concrete surfaces. They're not the same as the domestic products you'll find in a garden centre.

When applied correctly, biocide doesn't just kill what's visible. It penetrates into the pores of the surface and leaves a residual treatment that inhibits regrowth for an extended period.

How long on different surfaces

Driveways and patios — 6 to 12 months

Hard-standing surfaces take the most punishment: foot traffic, vehicle weight, oil, grit, and constant wet/dry cycles. Biocide on a driveway or patio typically stays effective for 6–12 months depending on usage and weather exposure.

A north-facing driveway that stays damp will see faster regrowth than a south-facing one that dries quickly. Overhanging trees are the biggest enemy — they deposit organic matter that feeds algae and moss year-round.

Roofs — 3 to 5 years

Roofs see far longer biocide longevity. Less foot traffic, less contamination, and the biocide treatment bonds well to the tile surface. Most customers we've treated see 3–5 years with no visible regrowth. That's why we can offer a 3-year guarantee with confidence.

Render and brick — 1 to 3 years

Rendered walls vary widely. K-Rend and similar modern renders hold biocide well and can stay clean for 2–3 years. Older pebbledash or painted surfaces are more porous and may need retreating annually in wet locations.

Signs it's time for a retreatment

You'll know the biocide has run its course when you start seeing black streaks forming (algae), small patches of green (early-stage moss), or a general dulling of the surface colour. At this stage, it's much easier and cheaper to apply a maintenance treatment than to wait until there's a full growth requiring a complete re-clean.

Can you retreat without a full re-clean?

Yes. If the surface is still generally clean and the growth is only just starting, we can apply a biocide retreatment without a full pressure wash. This is significantly cheaper and extends the life of the original clean considerably.