Soft washing a house means cleaning the siding, soffits, and trim with a diluted bleach mix at low pressure instead of blasting it with a pressure washer. The chemistry kills the algae and mold. A high-volume, low-pressure rinse carries the dead growth off. For the term itself and where it came from, read our what is soft washing guide. For the mechanism behind it, the how does soft washing work breakdown covers the chemistry and the physics.
We build the metering gear and we take the calls when a wash streaks or the landscaping burns. So the ratios and dwell times below are the ones that keep a job from coming back on you. Here's how to soft wash a house, start to finish.
The process at a glance
- Walk the house and read each surface. Vinyl, Hardie, stucco, brick, and painted wood don't take the same mix.
- Mix to the surface, not the house. Around 1% SH at the wall handles most siding. Different surfaces want different strengths.
- Pre-wet and protect. Soak the plants, tape the outlets, bag the downspouts, cover what can't get wet.
- Apply the mix low to high. Under 100 PSI at the gun, soap from the bottom up so it doesn't streak.
- Let it dwell. Five to fifteen minutes, surface wet the whole time, never let it dry.
- Rinse top-down. Low pressure, high to low, windows last and three times over.
- Rinse the plants again and walk the job. Flush the landscaping, check your work up close, fix any drips.
The rest is each step, with the real numbers.
Step 1: Walk the house and read each surface
Before you pull a hose, walk the whole property. Figure out the wind direction and your order of attack. Note the spigot, the koi pond if there is one, the dark cars in the driveway, and which sides are shaded. The north and shaded sides hold the most growth, so plan to hit those first and save the front for last.
Then read the siding. Run a gloved finger down the wall, especially on the south-facing side that takes the most sun. If it leaves a chalky white streak, the surface is oxidized, and that changes everything. Soft washing removes organic growth. It does not remove oxidation, and high pressure on an oxidized wall leaves permanent stripes that look like zebra marks. Tell the homeowner up front that 1% SH won't lift the oxidation, then sell oxidation removal as its own service if they want it.
A few surfaces are the wrong call for a standard wash. Skip the SH and quote something else when you see chalky failed paint, peeling or failing caulk, organic-pigment paints in red, blue, or green that can bleed, or a pre-1978 home where the paint may contain lead. On bare or freshly stained wood, use water only. SH is hard to rinse out of wood and it interferes with stain and paint adhesion.
Last, document. Record a quick walk-around video and four corner photos before the first drop of water. That's the only way to prove a crack or a warped panel was there before you arrived. Look through the glass to spot hardwood floors that could warp, confirm the windows are closed, and flag any AC units that stick out from the wall.
Step 2: Mix to the surface, not the whole house
The biggest mistake on a house wash is one ratio for the whole building. Mix to the surface in front of you.
For most siding, the standard is about 1% SH at the wall. You get there by running 12.5% stock through a downstream injector, which is roughly 99% water by the time it leaves the nozzle. A 2.1 injector on a 4 GPM machine lands just under 1% at the surface, and that handles a home that hasn't been cleaned in two years. What's in the jug and what hits the wall are two different numbers, and that gap is the whole point of downstreaming. If you want the math on injectors and whether your pressure washer can run this, our can you soft wash with a pressure washer guide walks through it. The short version: a downstream injector tops out around 1.5% at the surface, so anything stronger needs a dedicated 12V pump or an X-Jet.
Add a surfactant when you want the mix to cling and dwell, which helps on cold days and heavily shaded walls. Skip it on windows, screen enclosures, and metal, where it leaves a film or extends the rinse forever. For most light algae on vinyl, SH alone does the job. Our surfactant guide covers when it earns its place, and the sodium hypochlorite breakdown covers mixing from stock.
Here's where each surface lands. Every percentage is the strength at the wall, not the strength in the jug.
| Surface | Target SH at the surface | Dwell | Max pressure | Key caution |
|---|---|---|---|---|
| Vinyl siding | ~1% (0.5 to 1.5%) | 10 to 15 min, keep wet | Under 100 PSI | Dark vinyl, or vinyl under four years old, flash-oxidizes. Pre-wet, skip surfactant, rinse fast, no dwell. Oxidized vinyl is not an SH job. |
| Fiber cement (Hardie) | 0.7 to 1% (lower on painted) | 5 to 10 min | Under 100 PSI, 5° tip, never a 0° tip | Dries very fast, so work small sections. Improper cleaning can void the James Hardie warranty (James Hardie). Test dark panels first. |
| Stucco | 1% or less | Until color changes, keep wet | Low pressure only | Discolors fast above 1%, so go over a second time at 1% rather than going stronger. Paint discoloration is permanent. |
| EIFS | 1% or less | Until color changes, keep wet | No pressure, soft wash only | Tap it. A hollow sound means foam backing. Light mechanical encouragement with a dual-lance wand only after the color changes. |
| Brick | ~1% for organic growth; 2 to 4% via a dedicated pump for heavy black algae (J. Racenstein) | 5 to 15 min | High volume, low pressure, light mist rinse | Don't over-dwell on shaded brick, which etches. On porous brick the mix turns the algae white but won't remove it, so a low-pressure rinse does the lifting. |
| Painted wood | ~1%, patch-test first | 5 to 10 min | Low pressure | Red, blue, and green organic-pigment paints can bleed. Bare or newly stained wood gets water only. |
| Aluminum siding | ~1%, reduce surfactant | Keep wet, don't dwell in sun | Low pressure | SH dwelling on hot painted aluminum strips paint at any strength. Test unknown or galvanized metal on a small spot first. |
Start low and go up if you need to. You can't undo an over-strength application, and the damage shows up on the paint, the siding, and the landscaping. When a wall needs more, a second coat at 1% beats one stronger batch nearly every time.
Step 3: Pre-wet and protect plants, pets, and property
This is the step that saves you from callbacks and lawsuits, and most operators rush it.
Pre-wet every plant before any chemical touches the wall. A plant full of water resists chemical uptake. A dry plant pulls runoff straight in. Soak the two-to-three-foot zone out from the wall until the grass is soggy underfoot, and keep water on the sensitive plantings the whole time you work. In Florida heat, plan on about two minutes per plant. SH is toxic to plants and aquatic life, and the runoff is not allowed to enter storm drains, lakes, or streams (EPA NPDES; OSHA Sample SDS). On a property with a koi pond, walk the downspout connections first. One drop of bleach can kill the fish, and runoff travels through underground downspout lines you can't see.
Cover what can't get wet. Use Tyvek house wrap over tall and high-value plants, not a solid tarp, because a tarp traps heat and moisture and cooks the plant from the inside. Bag or divert every downspout before you apply chemical. Tape the electrical outlets, the doorbell and cameras, and the lock cylinders, since SH wicks into a lock tumbler and ruins it, and it permanently blackens bronze and dark hardware.
One honest note on neutralizer. A liquid bleach neutralizer does not protect a leaf, because SH starts burning foliage within a few seconds, faster than any neutralizer can act. The real protection is covering the plant and flooding its roots. Neutralizer is a supplemental rinse afterward, not your front-line defense. For the deeper safety picture, see our is soft washing safe guide.
Step 4: Apply the mix at low pressure
A house wash runs at about 100 PSI at the gun. Compare that to the 1,500 to 3,000 PSI a pressure washer puts out. The pressure isn't cleaning anything here. The chemistry kills the growth, and the water volume rinses it off.
Soap the siding from the bottom up. When you soap top-down, the mix runs down over dry siding, the water evaporates, and the SH concentrates into streaks at the base. A 1.5% mix can effectively reach past 1.8% in a dried run-down line, and that's where damage starts. There's a minority of operators who soap top-down to keep water from driving behind siding laps, and it's worth knowing both sides exist. The point everyone agrees on is that you always rinse top-down.
Work the house in pairs of sides, not all at once. Soap two sides, let them dwell, rinse those two, then move to the next pair. Stagger it so one section dwells while the previous one rinses. By the time you walk back, the first side has had its five to ten minutes. Wrap each corner with a six-to-eight-foot overlap so you don't leave a clean line. Think two or three steps ahead instead of chasing raw speed.
Step 5: Let it dwell
Five to fifteen minutes is the working window. Light algae on a maintained home needs the low end. Heavy five-year growth on a shaded north wall wants the high end, sometimes a second coat.
Keep the surface wet the entire dwell and never let the mix dry. When SH dries on a wall, the concentration climbs from under 1% toward the strength of the raw stock, and that's what flash-oxidizes vinyl and leaves a chalky residue you have to scrub off by hand. Heat works for you and against you. It speeds the kill, so dwell is shorter on a hot sunny side, but it also dries the mix faster, so you rinse those sides sooner. Cold and shade stretch the dwell out. Lay a light, even coat rather than a flood, because the reaction needs oxygen and a soaked surface just runs off.
Step 6: Rinse top-down at low pressure
Rinse high to low, every time, on every surface. Rinsing the upper area first keeps drips from re-dirtying what you already cleaned.
Give the windows three rinses, not one. Debris flushed off the glass lands on the siding below and has to be chased down. Always rinse above a window before the glass itself. Hit the spots that cause callbacks: the soffit lip, behind the shutters where mud-dauber nests hide, and the gutter faces, which usually need two or three soap passes to come clean. Step in close and look up under the siding courses. A view from the driveway hides the green that's still sitting under a lap.
Step 7: Rinse the plants again and walk the job
Post-rinse all the vegetation once more after the wash. Flush the soft-wash line with fresh water for about thirty seconds at the end, which clears the SH and gives the plants a final rinse at the same time. Apply a neutralizer over the treated plantings if you used a stronger mix near them.
Then walk the house dry-eyed for leakers. Brown drip streaks off the roofline or the drip edge mean you under-rinsed a ledge or some horizontal trim. Wait for the dripping to stop, wipe with a damp rag, and re-rinse. If a painted surface shows any damage mid-wash, stop, record video, and call the homeowner before you do anything else.
Three surfaces that need extra care
Hardie, dark vinyl, and brick each need a closer look before you spray.
Hardie and fiber cement dry faster than vinyl. If your pre-wet is half dry in two minutes, the wall is too hot, so wet it twice and work the hottest sides in smaller top-and-bottom sections. James Hardie's own guidance is low-pressure water and a soft, non-metal brush, and it states that damage from improper cleaning may not be covered under warranty (James Hardie). Some painted Hardie, especially dark blue panels, reacts to SH and turns green or pink, so test a hidden spot first.
Dark and new vinyl carry real flash-oxidation risk. On colors like blue, maroon, and chocolate, and on siding under four years old, don't use surfactant, pre-wet hard, apply a minimal coat, and rinse almost immediately with no dwell. Light coat, rinse, repeat beats one heavy coat.
Brick doesn't grow algae the way vinyl does, so the visible change on a brick house is usually the fascia and trim, not the brick. Soap brick top-down, the opposite of siding, since upper runoff drips onto rinsed brick below. Rinse it with a light mist, because rinsing brick too hard pushes water into the weep holes and leaves spots after the job. On shaded brick, don't let the chemical sit too long, since thin-set and shaded brick etch easily.
The mistakes that streak or damage a wash
The common failures aren't mysteries. They're shortcuts.
- One ratio for the whole house. Vinyl, stucco, and brick don't share a number. Mix to the surface.
- Letting the mix dry, or washing in direct sun. Dried SH concentrates and oxidizes the wall. Keep it wet, rinse sun sides sooner.
- Skipping the plant pre-wet. Dry plants drink the runoff. You will burn the landscaping.
- Soaping top-down. Run-down lines dry and concentrate into streaks at the base.
- Pressure on oxidized siding. A 0° tip on chalky vinyl leaves pencil marks that look permanent.
- Mixing SH with any acid. This produces toxic chlorine gas, and it is genuinely lethal, not just an irritant (OSHA Sample SDS). Rinse all SH off a surface completely before you ever apply an acid-based product, and never combine them in a sprayer.
When a house wash is a pro's job
Some houses aren't a quick wash, and a homeowner who asks whether to do it themselves deserves a straight answer. The honest answer starts with the chemical. The job runs on sodium hypochlorite at working strength, and the 12.5% stock causes severe skin burns and eye damage and is very toxic to aquatic life (OSHA Sample SDS). Reaching a second-story gable or a roofline means working off a ladder, and the chemistry can make footing slippery. ARMA, the asphalt roofing trade body, recommends that only trained professionals work on a roof, and it warns that pressure washing an asphalt shingle roof causes granule loss and likely premature failure (ARMA). Get the siding mix wrong and that homeowner can void a manufacturer warranty.
That's why most of this work goes to a pro, and it's the rate you quote against. These washes pay about $0.30 to $0.70 per square foot, or roughly $450 to $1,000 on a two-story home depending on size and roof pitch (Swivl, 2025; Top Care Cleaning). A homeowner who wants it done without the chemical and fall risk is looking for a certified operator, the kind SoftWash Systems trains and holds to the ARMA cleaning standard.
If you're building toward running this work yourself, the concentration is where the whole job lives. Dial in the exact mix for each surface with our Soft Wash Mix Calculator before your next job.
Frequently asked questions
What mix do you use to soft wash a house?
Sodium hypochlorite, water, and sometimes a surfactant. You mix from 12.5% stock down to about 1% at the wall for most siding, run through a downstream injector that's roughly 99% water at the nozzle. Stucco and EIFS go lower, near 1% or under.
Can you soft wash a house with a regular pressure washer?
A pressure washer plus a downstream injector becomes a low-pressure soft wash system, applying at under 100 PSI. It applies at about 1% SH at the surface, which handles siding but can't reach roof strength. Our guide on soft washing with a pressure washer covers the setup.
How long do you let the solution dwell?
Five to fifteen minutes, depending on how heavy the growth is and how hot the wall is. Keep the surface wet the whole time and never let it dry. Dried SH concentrates and can oxidize vinyl. Heat shortens the dwell, while cold and shade stretch it out.
Does soft washing damage plants and landscaping?
Not if the operator pre-wets and manages runoff. SH is toxic to plants and aquatic life, so plants get soaked before, during, and after, and downspouts get bagged (EPA NPDES). Covering with breathable wrap and flooding the roots is the real protection, not neutralizer.
How long does a house soft wash last?
On siding, commonly one to three years before growth returns, longer in dry, sunny climates and shorter on heavily shaded, humid lots. Roofs often hold up longer. The reconciling factor is exposure: shade, humidity, and tree cover all bring the algae back faster.
