Soft washing: killing the growth, not blasting it
The low-pressure chemical method used on everything a pressure washer would wreck. What is in the solution, what it does to the organism, why the green comes back - and how to hire someone who understands all three.
What is soft washing?
Soft washing cleans an exterior surface with a dilute cleaning solution applied at low pressure and given time to work, then rinsed off - instead of removing growth with mechanical force. It exists because the discolouration on most houses is living: algae, mildew, lichen and moss with roots into the surface. Pressure removes what is on top and leaves the organism behind. Chemistry kills it, which is why a soft wash both looks better and stays clean longer on the same wall.
How soft washing actually works
Identify the organism, then the substrate
Algae, mildew, moss and lichen respond differently and sit differently on the surface. Lichen and moss are anchored and need longer contact; surface algae releases quickly. What the surface is made of then sets the concentration and the contact time that are safe.
Watch forA quote given without anyone looking at the growth. Lichen on rendered masonry and a light algae film on vinyl are the same colour from the street and completely different jobs.
Dilute to the surface, not to the stain
Soft wash solutions are cleaning agents and surfactants mixed down with water. The surfactant is what makes the mix cling to a vertical surface long enough to work rather than running straight off. Concentration is set by what the substrate will tolerate.
Watch forMixing strong "because it is bad". Over-concentrated solution on painted wood, aged paint or aluminium can dull, streak or lift the finish, and there is no going back from that.
Soak the landscaping first
Every bed, shrub and lawn edge within reach of overspray and runoff is watered thoroughly before anything is applied. Saturated foliage and soil dilute what lands on them instead of drawing it up.
Watch forA crew that only rinses plants afterwards. After is too late - the damage is done in the first minutes of contact.
Apply low, and let it dwell
Solution goes on at low pressure through a wide fan or a dedicated soft wash tip, bottom-up, and is left for a few minutes. Dwell time is the active ingredient of the whole method - this is where the organism is killed rather than displaced.
Watch forSolution drying on the surface. On a hot sunny elevation it can dry before it has worked, leaving pale ghosting and an unkilled wall. Competent crews re-wet, or move to the shaded side and come back.
Rinse thoroughly and neutralise the surroundings
The rinse is top-down and continues until residue is gone, not until the surface looks clean. Planting and hard landscaping in the runoff path are rinsed again afterwards.
Watch forA short rinse. Residue left behind is what causes the film on glass, the patchy screens and the plant damage that shows up two days later.
What does soft washing cost?
Soft washing is usually quoted as part of a whole-surface package rather than by the hour, priced on area, access and how established the growth is. Heavy lichen and moss take more solution and more dwell and cost more than a light algae film. The Cost Guide sets out the pricing structure.
See the full soft washing cost guide - by material, size and region →
If the number is the problem, here are the ways people pay for it →
Exterior cleaning tools → Work out area and method before you take quotes.
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When soft washing is the wrong call
When saying yes is the wrong move:
- The problem is not alive. Rust bleed, tannin staining from overhanging trees, oil, efflorescence and artillery-fungus spotting are not organisms and a soft wash will not shift them. Each needs its own targeted treatment, and being told otherwise is the clearest sign of a contractor guessing.
- It is your roof. Roof washing has different access, different risk and a different insurance profile, and it belongs to a dedicated roof cleaning trade. Have it quoted as a roof job by someone who does roofs, not added to a wall wash.
- The coating is already failing. Soft washing does not have the force to strip sound paint, but it will finish off paint that is already peeling or blistering, and it will make heavily chalked paint look blotchy. If the finish is at the end of its life, this is a repaint, not a wash.
- Your planting is precious and directly against the wall. Mature specimen shrubs, established ferns and anything in tight beds under the elevation being washed are genuinely at risk. If you would be devastated to lose them, either have them physically covered or accept that some elevations should be hand-cleaned instead.
- You need it to be permanent. Nothing in exterior cleaning is. Soft washing extends the interval because it kills rather than displaces - it does not stop new spores landing on a damp, shaded wall.
- Runoff has nowhere safe to go. On a property that drains straight to a watercourse, a bare storm drain or a neighbour's ground, containment or a different method has to be planned before work starts, not improvised on the day.
Types of soft washing
| Option | What it means for you |
|---|---|
| Soft washing vs high-pressure washing | The full side-by-side, with the surface matrix. |
| Roof cleaning | Roofs are soft washed too - by a different trade. |
| Common exterior staining | Identify what you are actually looking at first. |
What to check when hiring for soft washing
- What is in your solution, and at what dilution for my surface? You are not testing them on chemistry - you are testing whether the dilution changes by substrate. A single answer for every surface means a single mix in the tank.
- How long do you let it dwell, and what do you do on a hot sunny wall? Dwell is the method. "We re-wet so it cannot dry, or we work that elevation in shade" is the answer of someone who has done this properly.
- Do you carry a pesticide or applicator licence if my state requires one for this work? Some jurisdictions regulate applying certain biocidal treatments to exterior surfaces. Requirements vary and the contractor should know their own state's position without hesitating.
- What is your plant protection routine, before and after? The correct answer includes pre-soaking. If they only mention rinsing afterwards, they have the sequence wrong and your beds will show it.
- Will there be a smell, and how long does it last? There usually is one during and shortly after the work. Being told in advance is the difference between a normal job and a panicked phone call.
- What is your realistic expectation for lichen and moss on my surface? Anchored growth sometimes leaves a shadow after the organism is dead and needs a second visit or simply time to weather off. Get that expectation set before, not after.
- How long before this needs doing again on a house like mine? A local operator who has cleaned comparable properties for years can answer this specifically. A vague "a few years" means they have not been back to look.
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Sources
Sources last checked
- Water runoff and cleaning chemicalsU.S. Environmental Protection AgencyRetrieved 2026-08-04Stormwater discharge context when exterior cleaning enters drains.
- Occupational Employment and Wages — Construction TradesU.S. Bureau of Labor StatisticsRetrieved 2026-08-04Labor cost context for home-services trades nationally.
Sources for figures and claims on this page.
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