How to Remove Black Spots from Your Patio – The Complete Guide
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How to Remove Black Spots from Your Patio – The Complete Guide
Black spots on patios are one of the most frustrating outdoor cleaning problems. You scrub, jet wash, even try “miracle” cleaners — and they still come back. If your paving is covered in small black marks that won’t shift, you’re not dealing with dirt at all. You’re dealing with a living organism. In this guide, you’ll learn exactly what those black spots really are, why common cleaning methods fail, and how to remove them properly. We’ll also show you how to stop them returning, so you’re not fighting the same battle every year.
What Are Black Spots on Patios?
Those stubborn black spots are not dirt, staining, or mould. They are lichen — a slow-growing organism made from a partnership between algae and fungus. This matters, because unlike dirt, lichen doesn’t just sit on the surface. It actively grows into stone.
Lichen spreads through microscopic spores that land on paving and settle into tiny pits and pores in the surface. Once established, it attacks stone in two ways.
First is the physical attack. Lichen sends thread-like structures called hyphae into the stone. These act like roots, anchoring the organism tightly inside the surface. This makes the growth physically embedded, rather than just resting on top.
Second is the chemical attack. Lichen produces weak acids — particularly oxalic acid — that slowly break down the minerals in stone. This softens the surface, allowing the organism to penetrate even deeper and reinforcing its grip.
What you see on top is just the visible growth. The real organism is already inside the stone. In other words, black spots are the tip of the iceberg. That’s why they are so hard to remove, and why surface cleaning alone never works.
Why Pressure Washing and Scrubbing Don’t Work
Pressure washing is the most common way people try to remove black spots — and it’s also one of the least effective long-term solutions.
Pressure washing blasts off surface growth, but it does nothing to destroy the lichen’s underground root structure. The visible marks may fade temporarily, but the organism is still alive inside the stone, ready to regrow.
Worse still, pressure washing often makes the problem return faster. High-pressure water roughens the surface and increases porosity, creating more anchor points for spores. It’s like ploughing a field and then wondering why weeds come back stronger.
Scrubbing fails for the same reason — it only removes what you can reach.
Household cleaners also fail because they aren’t designed to penetrate stone. They may brighten the surface slightly but can’t reach deep enough to destroy the organism.
Even bleach only lightens the surface colour and rarely reaches the roots. Once it fades or washes away, the black spots return.
The core problem is this: most methods treat the symptom, not the cause.
How to Actually Remove Black Spots
To remove black spots properly, the treatment must penetrate the stone and kill lichen at root level.
This requires a specialist cleaner designed for biological growth rather than surface dirt.
Here is the correct process:
-
Clear the surface
Remove loose dirt, leaves and debris so the product can reach the stone directly. -
Apply evenly
Use a garden sprayer to coat the surface evenly. The stone should appear wet, but not flooded. -
Allow full penetration
Do not rinse. This is critical. The product must soak into the surface and reach the root system. -
Wait and assess
You should see the first signs of change after 1–2 weeks. Black spots usually fade gradually rather than disappearing overnight. -
Repeat if necessary
Very old or deeply embedded growth may need a second application after several weeks.
Timeline expectations:
Initial improvement: 1–2 weeks
Major visible change: 3–4 weeks
Full result: 6–8 weeks
Severe cases: up to 12 weeks
Need an effective black spot remover? See Patio Guard.
How to Stop Black Spots Coming Back
Removing lichen is only half the solution. Prevention stops the problem returning.
The most effective long-term approach is annual treatment with a preventive spray. This kills new spores before they establish.
You can also improve the conditions that cause lichen to thrive:
Reduce shade where possible by trimming back plants and trees.
Improve drainage so water doesn’t sit on the surface.
Increase airflow by clearing blocked edges and gaps.
Sweep your patio regularly to remove spores before they settle.
You may also consider sealing your patio after cleaning. A sealer reduces porosity, making it harder for organisms to attach in the first place.
Black spots don’t disappear on their own — but once you treat them correctly and prevent their return, they don’t have to control your patio again.