Green algae on concrete is removed most effectively by applying a sodium hypochlorite solution as a pre-treatment to kill the organism, then pressure washing at 3,000 to 4,000 PSI with a surface cleaner to remove the dead material. Pressure washing alone without chemical pre-treatment removes the visible algae surface layer but leaves live organisms in the concrete pores, leading to rapid regrowth.
Why algae grows on concrete patios in Fort Worth
Concrete patios are horizontal surfaces that collect moisture and organic material. Shaded patios, those under trees or covered by pergolas, stay wet longer after rain and do not receive the UV exposure that slows algae growth on sunlit surfaces. The spring pollen season in the DFW area deposits organic material on every outdoor surface, feeding algae spore colonization. DFW's clay-heavy soil also contributes moisture and nutrients when soil particles wash onto the concrete surface. The combination of shade, moisture, and organic material creates ideal algae conditions on many Fort Worth patios.
The kill-first approach
Green algae is a living organism with growth structures that penetrate into the porous concrete surface. High-pressure water removes what is visible on the surface but cannot reach into the pores where the algae is anchored. When those root structures survive, regrowth begins quickly, often within weeks in moist, shaded conditions. Applying sodium hypochlorite before pressure washing kills the entire organism, including the structures in the concrete pores. Dead algae does not regenerate.
The process for algae removal on concrete patios
- Pre-rinse surrounding vegetation: Wet down plants, grass, and landscaping adjacent to the patio before applying chemistry.
- Apply sodium hypochlorite solution: Apply a diluted SH solution to the algae-covered concrete. The appropriate concentration depends on how heavy the growth is.
- Allow dwell time: Give the solution time to kill the algae. You will often see the green color begin to fade or turn brown as the organism dies.
- Pressure wash: Apply 3,000 to 4,000 PSI with a surface cleaner. The surface cleaner covers the area evenly and prevents striping.
- Rinse surrounding area: Rinse landscape beds again to dilute any chemistry runoff.
What makes green algae on concrete slippery
Algae on concrete creates a biofilm, a thin, water-retaining layer of living organisms, that becomes extremely slippery when wet. A concrete patio that appears only slightly green can be hazardous underfoot after rain. This is not just an aesthetic issue. Slip-and-fall injuries on algae-coated surfaces are a real hazard, especially for older adults and children. Regular cleaning that keeps algae from establishing eliminates this risk.
How long before algae returns
After a proper kill-and-clean treatment, most Fort Worth patios stay algae-free for one to two years in shaded conditions and longer in full sun. Shaded patios with consistent moisture may see regrowth within 12 months. Reducing shade (trimming overhanging branches), improving drainage so water does not pool, and keeping organic debris off the patio surface all extend the interval between cleanings.
Does sealing a patio prevent algae?
A quality concrete sealer reduces surface porosity, which makes it harder for algae spores to colonize the concrete. It does not make concrete algae-proof, but it slows the growth cycle by limiting the moisture and nutrients available to surface organisms. Sealed concrete is also easier to clean when algae does eventually appear.
Professional patio cleaning in Fort Worth
CARE handles algae removal on concrete patios across Fort Worth and surrounding cities. Call (945) 275-8031 or visit our concrete cleaning page to schedule a cleaning.