Black Spot on Your Driveway: What It Is and How to Get Rid of It

You scrub it with a brush. You spray it with household cleaner. You pressure wash it. And it comes back. Sound familiar? That's because 99% of people are treating a biological problem like it's a dirt problem. Black spot isn't oil. It's algae. And it needs a completely different approach.

What black spot actually is

Black spot — that dark staining you see on driveways, patios, and block paving — is Cladosporium herbarum, a microscopic algae. It thrives in damp, shaded conditions. It bonds to the surface of your concrete or stone and spreads through spores. Once established, it's very difficult to remove and very easy to bring back if you don't address it correctly.

The reason it looks so stubborn is because it's not sitting on the surface like dirt. It's colonising the pores of the concrete and growing into the material. Scrubbing attacks the symptom, not the cause.

Why your pressure washer won't fix it

A domestic pressure washer (or even a professional one without the right chemicals) can blast off the visible algae, but it doesn't kill what's deep in the pores. Within weeks or months, the spores germinate again and the black spot returns. You're in a loop: clean, regrowth, clean again, regrowth again.

This is why every "hack" you see online fails. Bleach? It kills the surface growth but the deeper colonies survive. Vinegar? Same problem. Domestic deck cleaners? Too weak to penetrate. High pressure alone? Pointless against algae.

Why household products don't work

Domestic cleaners are designed to remove dirt and grease. Algae is a living organism with a protective cellular structure. Most household products don't have the chemical composition to penetrate that structure and kill the organism at source. They might lighten the surface but they leave the root alive. That's why the stain comes back.

Bleach is particularly useless. It's corrosive and will damage the concrete surface over time, but it doesn't penetrate deep enough to kill established algae colonies. You're damaging your driveway to fight a losing battle.

What professional biocide treatment does

Professional-grade biocide is a specialist chemical engineered specifically to kill biological growth. When applied after a proper low-pressure wash, it:

• Penetrates deep into the pores of the concrete
• Kills the algae colonies at their root
• Leaves a residual treatment that prevents regrowth for 6–12 months
• Won't damage the surface like bleach or uncontrolled high pressure

The correct process

This is how we approach black spot removal on driveways:

1. Inspection: We assess how deep the algae has colonised and whether the surface is otherwise sound.
2. Low-pressure wash: Clean the driveway using a pressure washer at controlled low pressure — enough to remove dirt and dead growth without damaging the surface.
3. Biocide treatment: Apply professional biocide to the clean surface. This penetrates into the pores and kills any remaining spores, then leaves a residual barrier against regrowth.
4. Optional sealing: For long-term protection, seal the driveway with Smart Seal to create a barrier that makes regrowth much harder.

Why it doesn't come back (for a while)

After professional treatment with biocide, black spot typically doesn't return for 6–12 months. That's not because we've banned algae from your driveway forever — it's because the biocide residue is still actively inhibiting growth. Once that residue wears off, you might start seeing early signs of return. That's when a maintenance treatment — just biocide, no full clean needed — keeps it at bay.

If you seal your driveway after cleaning, you extend that protection significantly. Sealed surfaces are harder for algae to colonise, so regrowth is much slower.

How to prevent it coming back

The best defence is regular maintenance. A biocide maintenance treatment every 12 months (way cheaper than a full clean) keeps your driveway genuinely clean year-round. If your driveway is shaded or damp, consider doing it every 6–9 months.

If possible, increase drainage or remove overhanging growth that keeps the surface damp. A driveway that dries quickly is a driveway that's harder for algae to establish on.