What is soft washing?
Soft washing is low-pressure cleaning where a solution, not a jet of water, removes the growth. The mix is applied through a wide, gentle spray, given time to break down mould, mildew, algae and lichen, and then rinsed off without force. Because nothing is being blasted, the paint, the plaster coating and the roof surface underneath are left intact.
The idea is simple. Mould and lichen are living things rooted into the surface, and spraying them hard only tears off what you can see. A solution that kills the growth reaches into the texture of weatherboards, the pores of plaster and the coated chip finish of a roof tile, places a jet would either miss or damage.
Soft washing is a method rather than a single job. We use it for a full house wash, for roof cleaning, and on fences, retaining walls and outdoor furniture that would scar under high pressure.
What does a soft wash use?
Most soft wash solutions are built on one of two active ingredients. Sodium hypochlorite, the same chemical found in household bleach, kills growth quickly and is common in exterior house wash products. Quaternary ammonium compounds such as benzalkonium chloride are the basis of most spray-and-leave moss and mould treatments. Surfactants are added so the mix clings to the wall instead of running straight off.
- Sodium hypochlorite washes: a fast, visible clean. A New Zealand exterior prep wash safety data sheet lists it at under 5% of the product, before dilution, and classes the product as harmful to aquatic life. It can etch glass and aluminium if left to dry, so joinery is rinsed promptly.
- Quaternary ammonium treatments: slower acting. They are usually left on and allowed to work with the weather over weeks, which suits roofs and lichen. Their safety data sheets class them as very toxic to aquatic life, so run-off control matters even more.
- Surfactants: the detergent part of the mix. They help the solution wet the surface and lift the loosened grime so the rinse carries it away.
Strength is matched to the surface and how much growth is there. Mixing different cleaning chemicals is never part of the method, because bleach combined with ammonia-based or acidic products gives off toxic gas.
Is soft washing better than pressure washing?
For walls and roofs, yes, because soft washing kills the growth without damaging the surface underneath. Pressure washing is still better on hard, unpainted surfaces such as concrete driveways and pavers, where force does no harm and lifts ground-in dirt quickly. Most jobs simply use each method where it belongs, which is why one visit often includes both.
We’ve set out the full comparison, including what water blasting can damage and how the costs compare, in soft washing vs water blasting.
Which surfaces need a soft wash?
Anything painted, coated or brittle needs a soft wash. That covers painted weatherboards, plaster and EIFS cladding, fibre-cement sheet, stained timber, and nearly every roof type, from painted iron to concrete tiles and decramastic. Roofs that may contain asbestos are the strictest case: WorkSafe prohibits high-pressure water on asbestos-containing material, so a low-pressure method is the only acceptable option.
Plaster and EIFS are the surfaces most easily hurt by a blaster. The finish coat is what keeps the weather out, and a chip or crack from a jet can let water into the wall. Painted weatherboards come next: pressure lifts paint at the edges and can drive water up behind the laps.
Roofs need particular care. WorkSafe’s safety alert on high-pressure spraying of roofs warns that buildings from before the 2000s may contain asbestos, and that decramastic tiles installed before asbestos was phased out may contain it too. In the case it describes, a 1970s house had its decramastic roof water blasted, and asbestos debris contaminated the property inside and out. If your roof is that age, we’ll plan for a soft wash or a spray-and-leave treatment from the start, and the crew stops and seeks specialist advice if suspect material turns up. For moss and lichen specifically, see roof moss treatment.
Is soft washing safe for plants, pets and stormwater?
It is when the job is planned properly. The solutions are diluted, plants along the walls are wetted before spraying and rinsed afterwards, and pets stay inside until surfaces are dry. Stormwater is the bigger concern: the active ingredients are harmful to aquatic life, so run-off must be diverted to lawn or garden and kept out of the drains.
Auckland Council’s pressure washing guidance treats moss and mould removers as potentially harmful chemicals, says they must not enter the stormwater system, and asks that they aren’t applied when rain is forecast. Diverting downpipes onto unsealed ground and blocking nearby drains are the standard controls.
A few practical points for the day: bring in washing from the line, move cars away from the walls, and close windows. Fishponds and vegetable gardens close to the house get covered, and if you collect rainwater from the roof, disconnect the tank before a roof wash and leave it off until the roof has rinsed clean in a decent shower.
How long do soft wash results last?
On walls, a soft wash usually keeps a house looking clean for around a year, which lines up with the yearly washing paint makers recommend. Shaded, damp or coastal sites come back sooner. Because the solution kills the growth rather than just knocking off the surface layer, regrowth tends to be slower than after a plain rinse, though no wash stops spores arriving.
Roofs work on a different clock. A spray-and-leave treatment often looks no different on the day, then improves over the following weeks and months as rain loosens the dead moss and lichen. How long a roof stays clear depends on shade, overhanging trees and roof pitch, so we’d rather tell you what to expect for your particular roof than quote a number that doesn’t fit it.
What soft washing costs in Auckland
Soft washing a three-bedroom single-storey house usually costs $300 to $520, and a two-storey home $450 to $800, going by published Auckland prices. Roofs are priced separately: a spray-and-leave treatment runs about $200 to $500 and a full soft wash and rinse $300 to $900. Size, pitch, height and how heavy the growth is all count, and we confirm the price after a look.
| Job | Typical range |
|---|---|
| House soft wash, single storey, 3 bedrooms | $300–$520 |
| House soft wash, two storey, 3–4 bedrooms | $450–$800 |
| Roof spray-and-leave treatment, standard home | $200–$500 |
| Roof soft wash and rinse, standard home | $300–$900 |
A guide only, built from prices Auckland operators publish (checked October 2026; figures quoted plus GST were converted). Roof size, pitch, height and how heavy the growth is all change the price. We confirm yours after seeing the property.
Questions people ask about soft washing
Is soft washing more expensive than pressure washing?
Not usually for a house. Published Auckland prices for a soft house wash sit in the same bands as any standard house wash, because the time on site is similar. The solution adds some cost, but there’s less risk of paying later for paint touch-ups or water damage. Roofs cost more than walls whichever method is used, because of the access and safety set-up.
How do you soft wash a house?
Downpipes are diverted and drains covered, plants are wetted, and windows closed. A diluted solution is sprayed on at low pressure, working from the bottom of each wall up, and left for several minutes to kill the growth. Everything is then rinsed from the top down with a gentle flow, and joinery and glass are checked so nothing dries on them.
Is a soft wash worth the money?
For most painted houses it is. A yearly wash removes the mould, salt and grime that break paint down, and paint makers link regular washing to a longer-lasting finish. Compared with the cost of an exterior repaint, a wash is a small outlay. It also lets you spot early problems, like flaking paint or a leaking joint, while they are cheap to fix.
Can soft washing damage paint?
Not when it’s done properly. The pressure is low and the solution is diluted to suit the surface. Problems come from mixes that are far too strong, from solution left to dry in hot sun, or from washing over paint that was already failing, which can lift loose flakes. Chalky or peeling paint should be pointed out before the wash starts.