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Soft washing uses low-pressure chemistry to safely kill and remove mold, algae, and grime from stucco, painted wood, and siding — without the surface damage that high-pressure washing causes. Here's exactly how to do it right.
Pressure washing uses high-pressure water (typically 2,000–4,000 PSI) to physically blast surface contaminants off a structure. It works extremely well for hard surfaces like concrete driveways and brick pavers — materials tough enough to withstand the force. But for a house's exterior walls, especially Florida stucco, that same force causes real damage.
Soft washing, by contrast, uses water pressure of 100 PSI or less — roughly the same as a standard garden hose. The actual cleaning power comes from a diluted sodium hypochlorite solution that chemically kills mold, mildew, algae, and bacteria at the root level. The dead organisms are then rinsed away gently with water.
South Florida's combination of heat, humidity, and frequent rain creates one of the most aggressive environments for exterior organic growth in the continental United States. Mold and algae that might take a decade to develop in a dry climate can appear on a freshly painted Florida stucco wall within 12–18 months. The organism isn't just cosmetically unpleasant — it breaks down paint bonds, traps moisture against the stucco substrate, and accelerates the deterioration of the underlying material.
Pressure washing removes the surface layer of growth but leaves the root system embedded in the porous stucco. Within weeks, the growth returns — often denser than before because the pressure washing loosened the surface pores. Soft washing kills the root system, dramatically extending the time between cleanings.
These surfaces should always be soft washed, never pressure washed:
The foundation of a soft wash solution is sodium hypochlorite — the same active ingredient in household bleach, but at a higher concentration. Pool-supply stores sell liquid chlorine at 10–12.5% concentration, which is the starting point for most soft wash mixes. A surfactant (soap) is added to help the solution cling to vertical surfaces instead of running off immediately.
| Surface Type | SH Concentration | Water Ratio | Active Chlorine % |
|---|---|---|---|
| Light mildew (stucco, vinyl) | 1 part SH (10%) | 4 parts water | ~2% |
| Moderate algae (stucco, wood) | 1 part SH (10%) | 3 parts water | ~2.5% |
| Heavy mold / dark staining | 1 part SH (10%) | 1 part water | ~5% |
| Roof algae (shingles) | 1 part SH (10%) | 1 part water | ~5% |
| Painted surfaces (max) | 1 part SH (10%) | 1.5 parts water | ~4% |
Add 2 oz of non-ionic surfactant (or dish soap) per gallon of finished mix to improve cling and cleaning efficacy. Always mix bleach into water — not water into bleach — to reduce splashing risk.
This step is non-negotiable. Before touching any chemicals, soak all vegetation within 10 feet of your home's foundation with plain water. Shrubs, flower beds, grass, and mulch should be thoroughly saturated — a saturated plant takes up far less chemical runoff than a dry one.
Close all windows and doors and cover any AC intake vents or open electrical boxes near the work area. Move potted plants well away from the walls you'll be treating. If you have a pool, check that return lines are closed or that the pool area is masked — sodium hypochlorite can temporarily affect pool chemistry if it enters in large amounts.
Based on the condition of your exterior walls, select your dilution ratio from the table above. For most Florida stucco homes with moderate algae and mold growth, a 1:3 ratio (1 part 10% sodium hypochlorite to 3 parts water) is the starting point. For heavily stained walls with black mold, go 1:1.
Mix in a 5-gallon bucket or directly in your pump sprayer. Add surfactant last — pour it gently to avoid foaming. Wear chemical-resistant gloves, safety goggles, and old clothes or a chemical coverall. Sodium hypochlorite bleaches fabric on contact.
This is the most counterintuitive part of the soft wash process — but it's critical for a streak-free result. Start at the bottom of each wall section and spray upward, working your way to the top of the section before moving laterally. This ensures that any solution running down flows over already-wet surface, preventing the tide marks and streaks that occur when chemical drips down a dry wall.
Apply the solution generously — you want the surface visibly wet and the solution actively foaming slightly from the surfactant. Don't rush; make sure all stained, discolored, and mold-affected areas are thoroughly saturated. Pay special attention to shaded areas (north-facing walls, corners under eaves) where growth tends to be heaviest.
With the solution applied, step back and let chemistry do the work. Allow 5–10 minutes of dwell time for light mildew, or 10–15 minutes for heavy mold and algae growth. You'll often see visual feedback — the green or black staining will begin to visibly lighten as the bleach kills the organisms.
Keep a close eye on the surface. In direct Florida sunlight, the solution can dry quickly — especially on warm, dark-colored stucco. If you see the surface starting to dry or the foam disappearing, lightly mist the area with plain water to reactivate the solution. You are not diluting it significantly — just keeping it wet and active.
When the dwell time is complete, rinse from the top of the wall downward using your garden hose or a pressure washer set to a low, wide-fan setting (under 500 PSI for stucco). Work in sections — rinse completely before moving to the next area. Let the rinse water run off the base of the wall and flush away from the foundation.
After rinsing the entire house exterior, give all surrounding landscaping, grass, and plants a final thorough rinse with plain water. This dilutes any chemical that reached the soil. Most plants that were pre-soaked and properly rinsed afterward show no ill effects from a standard soft wash treatment.
Florida homeowners often have extensive tropical landscaping that requires extra care during a soft wash. Here's a comprehensive protection approach:
While soft washing is remarkably versatile, there are surfaces and situations where it should not be used:
We bring professional-grade 12V soft wash equipment, properly calibrated chemical mixes, and 5+ years of South Florida experience. Licensed, insured, and rated 4.9 stars on Google.
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