The green, black, and gray patches on Florida driveways, walkways, and pavers are usually algae, mold, and mildew, which grow wherever moisture and shade linger. Pressure washing can clear them from concrete, but pavers need care: the wrong nozzle or technique can wash sand out of the joints. Fixing the moisture is what slows the stains from returning.
What those stains really are
- Green: algae, which thrives on damp, shaded concrete and pavers.
- Black or dark gray: usually mold, mildew, or dark algae, often along shaded edges and anywhere water sits.
- Orange or rust-colored: iron in irrigation well water, or rusting metal left on the surface.
- Brown: tannins from leaves, mulch, or fallen palm fruit.
- Dark spots in the middle of the drive: oil and tire marks. These aren't growth and usually need a degreaser.
Why Florida hard surfaces turn so quickly
Concrete and pavers are porous, so they hold moisture. Florida's humidity, daily summer rain, and shade from trees and walls keep surfaces damp, which is exactly what algae and mildew need. Sprinklers that hit the pavement, gutters that empty onto the driveway, and wet leaf litter all feed the growth.
It is also a safety issue. Algae and mildew are slippery when wet, which matters on walkways, steps, and pool decks.
Why pavers need more care than a plain slab
A concrete slab can handle strong pressure. Interlocking pavers sit on a sand bed and are locked together by sand in the joints. The Concrete Masonry & Hardscapes Association (CMHA) describes professional paver cleaning at pressures from about 1,000 to 4,000 psi, and says a wide-spray nozzle held at a low angle reduces the risk of washing sand out of the joints. It also notes that stabilizing the joint sand benefits pavements that are cleaned aggressively and regularly.
So the technique matters as much as the pressure number. The wrong tip, held too close, can empty the joints and roughen the surface.
How to clean a driveway or pavers safely
- Clear and protect. Sweep off loose debris, move furniture and planters, and wet down nearby plants.
- Treat the growth. Use a cleaner made for the surface and follow the label. Algae and mildew need time to loosen, and the product should stay off plants and out of storm drains.
- Wash with the right tool. On concrete, a surface cleaner (a spinning disc attachment) gives an even result and avoids stripes. On pavers, use a wide spray at a low angle and keep it moving so it doesn't carve into the joints.
- Rinse generously. CMHA notes that a large amount of water matters more to rinsing than high pressure.
- Let it dry, then refill the joints. Replace sand that washed out so the pavers stay locked in place.
- Seal only after cleaning. CMHA says all dirt, oil stains, and efflorescence must be removed before sealing, and the surface must be completely dry before most sealers go on.
How to keep the stains from coming back
- Redirect water. Aim sprinklers off the pavement and send downspouts away from the driveway.
- Let in sun and air. Trim branches and shrubs that shade the surface so it dries faster.
- Sweep regularly. Leaves, palm fruit, and mulch hold moisture and stain.
- Fix low spots. Puddles that linger grow algae first, so ask a contractor about drainage if water ponds.
- Clean before it builds up. Light growth comes off more easily than years of buildup.
- Ask about sealing. A sealer can help hold joint sand in place, but it has its own upkeep, so ask the installer or manufacturer what suits your pavers.
When to call a pro
Large or heavily stained areas, slick steps and pool decks, pavers with failing joint sand, and natural stone or brick are all good candidates for a professional. At Shine Otter we assess the surface first, because concrete, pavers, brick, and natural stone all respond differently to pressure, and then match the pressure, cleaning solution, and technique to it. See driveway & patio cleaning. Annual patio and driveway pressure washing is also included in our Premier and Ultimate VIP Home Care Memberships.
For the bigger picture on methods, read soft washing vs. pressure washing.
Frequently asked questions
Is the black stuff on my driveway mold?
Often it is mold, mildew, or dark algae growing on a damp, shaded surface. Oil and tire marks also look dark but are not growth, and they usually need a degreaser. A cleaning will show which one you have.
Can pressure washing damage pavers?
Yes, if the pressure is too high, the nozzle is too close, or the technique is wrong. It can wash sand out of the joints and roughen the surface. A wide spray at a low angle, and refilling the joint sand afterward, reduces the risk.
How long until the green comes back?
It depends on shade, moisture, and drainage. Damp, shaded areas regrow fastest, so fixing sprinkler overspray and drainage matters as much as the cleaning itself.
Sources & further reading
About Shine Otter
Shine Otter is a family owned and operated exterior cleaning company serving Southwest Florida, from Englewood and Venice to Cape Coral and Fort Myers. We handle window cleaning, roof and gutter cleaning, soft washing, driveway and patio cleaning, window screen cleaning, storm debris cleanup, and solar panel cleaning. Call or text (425) 977-5156 for a free quote. Meet the owners.