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Updated October 2026. Mix targets come from published soft wash supplier and operator guides, linked below.
The soft wash chemicals that clean almost every house are simple: 12.5% sodium hypochlorite (SH) to kill the algae and mildew, a surfactant to make it cling, and water to rinse. What separates a clean house from damaged plants and streaked siding is the mix strength at the wall, the dwell time and the rinse.
This guide covers each chemical, mix ratios by surface, a batch chart you can print, the math behind downstream injectors, and how to soft wash a house step by step.
The soft wash chemicals you need
| Chemical | What it does | Typical use |
|---|---|---|
| Sodium hypochlorite (SH), 12.5% | Kills algae, mold, mildew, moss and lichen | About 1% at the wall for siding, about 3% for roofs |
| Surfactant | Helps the mix cling, spread and dwell | Small dose per batch; follow the label |
| Odor masker | Covers the bleach smell for customers | Optional; follow the label |
| Neutralizer or plant wash | Protects plants after stronger mixes | Sprayed on treated plantings after rinsing |
Pros buy 12.5% SH from pool supply stores or chemical distributors. It’s about twice as strong as household bleach and loses strength in heat and sunlight, so buy it fresh and store it cool and shaded. Supplier J. Racenstein lists about 3% for roofs and 1% for siding (J. Racenstein).
Never mix SH with acids or ammonia-based cleaners. The reaction releases toxic chlorine gas. Keep rust removers and acid cleaners in separate tanks and rinse lines between products.
Soft wash mix ratios by surface
These are targets for the strength that lands on the surface, not in the tank. They come from SoftWash Technologies’ operator guide (SoftWash Technologies):
| Surface | SH at the wall | Dwell time |
|---|---|---|
| Vinyl siding | About 1% (0.5–1.5%) | 10–15 min |
| Fiber cement (Hardie) | 0.7–1%, lower on painted | 5–10 min |
| Stucco and EIFS | 1% or less | Until the color changes |
| Brick | About 1%; 2–4% for heavy black algae | 5–15 min |
| Painted wood | About 1%, patch-test first | 5–10 min |
| Aluminum siding | About 1%, less surfactant | Keep wet, avoid full sun |
| Asphalt shingle roofs | About 3% | 15–20 min |
If a wall is still dirty, do a second pass at 1% instead of a stronger first coat. Skip SH on chalky or failing paint, fresh stain and bare wood, which need water only or a different cleaner.
Batch mixing chart for 12.5% SH
If you run a 12V pump or a gas soft wash system, you mix the final strength in the tank. The math is simple:
Gallons of 12.5% SH = batch size (gallons) × target % ÷ 12.5
| Target strength | SH per 100-gal batch | SH per 50-gal batch | Typical use |
|---|---|---|---|
| 0.5% | 4 gal | 2 gal | Light mildew, delicate surfaces |
| 1% | 8 gal | 4 gal | Most house washing |
| 1.5% | 12 gal | 6 gal | Heavier growth on vinyl |
| 2% | 16 gal | 8 gal | Brick, heavy algae |
| 3% | 24 gal | 12 gal | Asphalt shingle roofs |
| 4% | 32 gal | 16 gal | Heavy roof algae, brick |
Fill the rest with water, then add surfactant per its label. If your SH has been sitting in the heat, it may be weaker than 12.5%, and the mix will be too.
Downstream injector vs 12V pump vs X-Jet
How you deliver the mix decides how strong it can be.
- Downstream injector: pulls chemical into the water after the pump of your pressure washer. It dilutes a lot: SoftWash Technologies says a downstream setup tops out around 1.5% at the surface, and its example of a 2.1 injector on a 4 GPM machine lands just under 1%. That’s enough for most house washing and the cheapest way to start.
- X-Jet or M5-style nozzle: mixes chemical at the gun, so it can reach roof-strength mixes with a regular pressure washer.
- 12V or gas soft wash pump: sprays the batch you mixed in the tank, so you control the exact strength. It’s the standard for roofs and for crews that soft wash every day. See our best soft wash system guide.
Starter gear on Amazon:
- General Pump 3–5 GPM chemical injector: Check price on Amazon
- YAMATIC adjustable downstream injector kit (3/8 in.): Check price on Amazon
- X-Jet M5 #13 kit for 4–4.5 GPM machines: Check price on Amazon
How to soft wash a house in 7 steps
- Survey and photograph. Walk the house, note chalky paint, failing caulk, bare wood and damaged siding, and take photos or video of every side before you start.
- Protect plants, outlets and drains. Soak plants and grass near the walls with water first. Cover high-value plants with breathable wrap, not a solid tarp. Tape outlets and divert or bag downspouts.
- Mix to the surface. Aim for about 1% SH at the wall for most siding (see the table above).
- Apply bottom to top. Spray at low pressure (under 100 PSI), working two sides at a time so you can rinse before anything dries.
- Let it dwell. Five to 15 minutes is the usual window. Keep the surface wet and never let the mix dry on the siding or windows.
- Rinse top to bottom. Rinse windows, trim and plants well. Rinse plants again even if they were pre-wet.
- Final walk. Look for drip streaks and missed spots, re-rinse, and spray neutralizer or plant wash on treated plantings if you used a stronger mix. Flush your chemical line with fresh water.
How to soft wash a roof
Roofs need a stronger mix (about 3%) and no pressure. The Asphalt Roofing Manufacturers Association advises a diluted bleach solution left on for 15 to 20 minutes, a gentle rinse, and no power washing or scrubbing, which can strip granules (ARMA). Check the shingle maker’s instructions, and use fall protection on any roof you walk. Our roof cleaning cost guide covers safety gear and pricing.
Safety gear and plant protection
- Chemical-resistant gloves: Check price on Amazon
- Sealed safety goggles: Check price on Amazon
- Bleach-rated pump sprayer for spot treatments and plant rinse products (Chapin 20075): Check price on Amazon
Runoff is also an insurance issue. Some general liability policies exclude damage from chemicals. Our pressure washing business insurance guide explains what to ask your agent. Check local rules about where wash water can drain, too.
What to charge for soft washing
A one-story house wash typically runs $150–$750 nationally, and a roof soft wash $350–$750, according to our pressure washing price guide. Price per square foot of living area, set a minimum, and add your chemical cost: at 1%, a 100-gallon batch uses about 8 gallons of SH. The estimate calculator handles house washes and roofs in one quote.
Software that sends quotes, reminders and review requests helps you turn one-time house washes into yearly customers.
How we compiled this guide
We didn’t run our own chemical tests. We compared published guidance from soft wash suppliers and operators (SoftWash Technologies, J. Racenstein) and the roofing industry (ARMA), then did the dilution math ourselves. Always follow the labels on your chemicals and the siding or shingle manufacturer’s instructions.
Related guides
- Best soft wash system (pumps, tanks and 12V setups)
- Soft washing vs pressure washing
- Roof cleaning cost and calculator
- How much to charge for pressure washing
- Pressure washing equipment list
- Best Soft Wash Pump: 12V vs 24V vs Gas
Frequently asked questions
What chemicals are used for soft washing?
Most pros use 12.5% sodium hypochlorite, a surfactant to help it cling, and sometimes an odor masker and a plant neutralizer. Water does the rest.
What is the soft wash mix ratio for a house?
About 1% SH at the surface for most siding. From 12.5% SH, that’s 8 gallons of SH in a 100-gallon batch, or 4 gallons in 50.
What is the soft wash mix for a roof?
About 3% for asphalt shingles: 24 gallons of 12.5% SH in a 100-gallon batch. Follow the shingle maker’s guidance and rinse gently.
Can I soft wash with a downstream injector?
Yes, for house washing. A downstream injector usually reaches around 1% at the surface, which handles most siding. Roofs need an X-Jet or a soft wash pump.
Can I use household bleach to soft wash?
You can, but it’s weaker (usually 5–8%), so you need much more of it. Pros use 12.5% SH because it’s cheaper per job.
Will soft wash chemicals kill plants?
They can if the mix sits on leaves. Soak plants with water before and after, cover high-value plants with breathable wrap, and use a neutralizer or plant wash after stronger mixes.
