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Green or black film on a Jacksonville driveway is almost always algae, sometimes with mildew and lichen alongside it. It is not dirt that settled there. It is an organism that has colonised the pores of the concrete, and it is thriving because your driveway offers everything it needs: moisture, warmth and often shade.
Why it keeps coming back
Concrete is porous. Algae anchors below the visible surface, not just on top of it. Rinse it with a hose and you remove the surface layer while leaving the colony intact — which regrows quickly, often within weeks in a Florida summer.
Three conditions on the First Coast make it worse than in most of the country:
- Humidity. Concrete here rarely dries out completely, especially overnight.
- Shade. Oak canopy over much of Mandarin, Riverside and Ortega keeps slabs damp all day.
- Irrigation. Sprinkler heads that catch the edge of the driveway keep a strip permanently wet. This is the single most common cause of a driveway that is clean everywhere except one recurring green band.
What actually removes it
The professional approach
- Pre-treat. A cleaning solution is applied and given time to break the algae down at the root. This step is what determines how long the result lasts, and it is the step most often skipped.
- Surface clean. A rotating surface cleaner covers the slab in even, overlapping passes at consistent distance, lifting the loosened growth and embedded dirt.
- Detail the edges. Expansion joints, edges and step risers finished by hand where the machine cannot reach.
- Rinse out. Everything flushed off the slab and away from landscaping.
The order matters. Pre-treating first means the machine is removing already-dead growth rather than grinding at living material — which is why a pre-treated driveway stays clean noticeably longer than one that was simply blasted.
If you're doing it yourself
- Use the widest spray tip that still works, and keep the wand moving.
- Never hold a narrow tip close to the slab. It etches lines that never come out.
- A rented surface cleaner attachment is a much better result than freehand wanding.
- Pre-wet and rinse surrounding landscaping before and after using any cleaning solution.
- Do not use a wire brush or acid on decorative or stamped concrete.
The most common DIY mistake: cleaning a driveway freehand with a wand. It produces the striped "zebra" pattern — arcs of cleaner and dirtier concrete — and once you see it, you cannot unsee it. Fixing it means recleaning the entire slab evenly.
How to slow it down between cleanings
- Adjust your sprinklers. Aim heads away from concrete. This one change makes a bigger difference than anything else on a lot of Jacksonville properties.
- Trim back overhanging branches where practical, to let more sun reach the slab.
- Clear leaf litter regularly. Wet leaves left on concrete cause tannin staining as well as trapping moisture.
- Improve drainage anywhere water pools after rain.
- Consider sealing after a thorough cleaning — it reduces porosity and slows recolonisation.
What about bleach or vinegar?
Household bleach diluted appropriately is a common DIY approach and does kill surface algae, but it needs care around landscaping, metal fixtures and adjacent surfaces, and it does not remove the embedded dirt that comes with the growth. Vinegar is popular online and is generally weak for this application on porous concrete. Neither substitutes for mechanical cleaning if you want the concrete to look uniform afterwards.
When it's not algae
If the staining is orange or rust-coloured, it is probably iron from well-water irrigation — common in Orange Park and Clay County — and it needs a rust treatment, not pressure. Dark brown patches under trees are usually tannin. Black spots that will not shift are frequently artillery fungus from mulch. Each needs a different treatment, which is part of why an on-site look beats guessing from a photo.
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