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Quick answer: soft wash SH mix ratios by surface
The standard soft wash mix is 1-3 percent sodium hypochlorite (SH) for house siding and 3-5 percent SH for roofs. Starting from 12.5 percent SH concentrate, that means mixing 1:6 to 1:12 for vinyl siding and 1:1 to 1:3 for asphalt roofs. Concrete runs 2-4 percent SH at 1:2 to 1:5. Always add 4-8 oz of surfactant per 5 gallons of mix to improve dwell time on vertical surfaces. Plan about 1 gallon of mixed solution per 50-100 sq ft. A 2,000 sq ft house exterior needs 3-6 gallons of 12.5 percent SH, costing only $10-$30 at $3-5 per gallon.
Getting the right bleach-to-water ratio is the most critical skill in soft washing. Too strong and you risk damaging surfaces, killing plants, and wasting chemicals. Too weak and the solution won't clean effectively, requiring costly re-applications.
The standard starting point is 1-3% sodium hypochlorite (SH) for house siding and 3-5% SH for roofs. Always add a surfactant to help the solution cling to vertical surfaces and improve dwell time.
| Surface | SH Strength | Mix Ratio | Notes |
|---|---|---|---|
| Vinyl Siding | 1 – 2% | 1:6 – 1:12 | Downstream safe |
| Brick / Stucco | 2 – 3% | 1:3 – 1:6 | Pre-wet plants |
| Asphalt Roof | 3 – 5% | 1:1 – 1:3 | No pressure |
| Concrete / Driveway | 2 – 4% | 1:2 – 1:5 | Pre-treat stains |
| Wood Deck | 1 – 2% | 1:6 – 1:12 | Rinse well |
| Tile Roof | 2 – 3% | 1:3 – 1:6 | Low pressure rinse |
Ratios shown assume 12.5% SH concentrate. Adjust proportionally for different source strengths.
The standard soft wash mix ratio is 1-3% sodium hypochlorite (SH) for house siding and 3-5% SH for roofs. Starting from 12.5% SH concentrate, this means mixing at ratios between 1:3 (strong, for roofs) and 1:12 (light, for vinyl siding).
Always add a surfactant (4-8 oz per 5 gallons of mix) to improve dwell time on vertical surfaces. The right ratio prevents surface damage while still killing mold, mildew, and algae on the first application.
For a typical 2,000 sq ft house exterior, you need 3-6 gallons of 12.5% SH mixed into 20-40 gallons of total solution (1-2% final strength). This breaks down to roughly 1 gallon of SH per 500 sq ft of surface area.
At $3-5 per gallon for 12.5% SH, your chemical cost for a house wash is only $10-$30 — making soft washing one of the highest-margin services in exterior cleaning. Most contractors charge $200-$600 for the same job.
Roof cleaning requires 3-5% SH final strength — stronger than house washing because roof algae (Gloeocapsa magma) is harder to kill. This means mixing 12.5% SH at a 1:1 to 1:3 ratio with water.
Never pressure wash a roof — the force will strip granules from asphalt shingles and void most manufacturer warranties. Soft washing with the correct SH concentration is the only approved cleaning method recommended by shingle manufacturers like GAF and CertainTeed.
For vinyl or aluminum siding, use a 1-2% sodium hypochlorite (SH) solution. This means mixing approximately 1 gallon of 12.5% SH with 5-10 gallons of water. For heavily soiled surfaces with mold or algae, you can increase to 3%. Always add surfactant (about 4-6 oz per 5 gallons of mix) to help the solution cling to surfaces.
Roof soft washing typically requires a stronger mix — 3-5% SH solution for asphalt shingles. This means about 1 gallon of 12.5% SH per 2-3 gallons of water. For tile or metal roofs, use a weaker 2-3% solution. Never pressure wash a roof — soft washing with the right chemical strength is the only safe method.
Plan for approximately 1 gallon of mixed solution per 50-100 square feet of surface area. A 2,000 sqft house exterior typically needs 20-40 gallons of mixed solution. Rough or textured surfaces absorb more solution. Our calculator gives you exact batch sizes based on your surface area and type.
Sodium hypochlorite (SH) is the active ingredient in bleach. Regular household bleach is 3-6% SH. For soft washing, buy professional-grade 10-12.5% SH from a chemical supplier. It's much more cost-effective than household bleach. Store in a cool, dark place — SH degrades in heat and sunlight, losing about 1% strength per month in summer.
Chemical costs for soft washing a 2,000 sqft house are typically $10-$25 (5-10 gallons of 12.5% SH at $3-5/gallon, plus surfactant). Most contractors charge $200-$600 for the complete job. The profit margin on soft washing is excellent because chemical costs are low relative to the job price.
Use a dedicated soft wash surfactant (not dish soap). Popular options include Cling-On, Elemonator, and Bio-Cling. Surfactants help the bleach solution stick to vertical surfaces instead of running off, improving cleaning power and reducing chemical waste. Add 4-8 oz per 5 gallons of mixed solution depending on the product.
