How to Remove Black Spots From Your Patio (And Why Jet Washing Alone Won't Fix It)

You've pressure washed the patio, it looks great for a day, and then you notice them: small, flat black dots clinging to the slabs that simply won't shift no matter how close you get with the lance. Here's the frustrating truth — those aren't dirt, and pressure alone will never remove them.

What the black spots actually are

They're lichen — a tough organism that bonds directly to the stone surface. Because it grows into the top layer of the slab rather than sitting on top like ordinary grime, blasting it with water just cleans around it and leaves the black core behind. Turn the pressure up high enough to remove it and you'll pit and scar the slab instead.

Why the "just power wash harder" approach fails

Three things happen when people try to force it:

• The surface gets etched and rough, which then traps more dirt and algae later.
• Natural stone and some concrete slabs lose their sealed top layer, so they stain more easily afterwards.
• The lichen roots survive anyway and regrow within a season.

What actually removes lichen

The reliable method is a specialist treatment, not brute force. A biocide or dedicated lichen treatment is applied, given time to break down the organism at the root, and then the surface is gently cleaned. On many patios this is a soft-wash approach rather than high-pressure blasting — it's the chemistry doing the work, not the water pressure.

Done properly, the black spots don't just disappear — they stay gone for far longer, because the roots have been killed rather than skimmed.

Keeping them away

North-facing and shaded patios that stay damp are the most lichen-prone. After a proper treatment, an occasional preventative wash and keeping the area free of standing leaves and debris slows regrowth significantly.

If your patio is speckled with black spots that won't budge, that's exactly the kind of job worth having treated properly rather than fighting yourself. Send a photo and we'll tell you honestly what it'll take.