Green algae grows on patios that stay damp and shaded, and it can make the surface dangerously slippery. Remove the surface growth first, then address the moisture conditions that allow it to return.
Remove loose debris and growth first
Sweep away leaves, soil, and organic debris before soaking the area. Dry or lightly damp brushing reduces the amount of cleaner needed and shows whether the green film is only on the surface or embedded in pores and joints.
Use a cleaner that matches the patio material
Concrete, natural stone, pavers, and wood do not tolerate the same products. Check the label and test a small area; avoid strong acids or concentrated bleach on sensitive materials or near unprotected plants.
Scrub without creating a slip hazard
Work in small sections with an appropriate brush and footwear that grips well. Do not stand on a soapy film, and keep children and pets away until the surface is rinsed and dry.
Reduce shade, standing water, and organic debris
If the patio stays wet for days, cleaning alone will not last. Improve drainage where practical, remove leaves regularly, and trim dense vegetation to increase airflow and light without damaging the surrounding area.
Sources
- American Cleaning Institute — Cleaning Tips — Household cleaning methods, product use, dosing, and material compatibility.