Soft wash or water blast?
Depends what you're washing. Soft washing vs water blasting isn't a fight, they're two different tools. A blaster's great on a concrete path and rough on your weatherboards. Here's what each one actually is, and what NZ paint, cladding and roofing makers say about them.
What's the actual difference?
Both get the grime off. They just come at it from opposite ends.
Water blasting, or pressure washing, uses a pump to fire water out hard. The force does the cleaning. It's quick, and on hard surfaces like concrete it works a treat. On softer stuff, that same force can strip paint, chew up timber and drive water where it shouldn't go.
Soft washing flips it round. A cleaning solution, commonly based on sodium hypochlorite, goes on at much lower pressure and gets to work on the mould, algae and lichen. It's given time, then rinsed off. Less force on the surface, more care with the chemistry.
Treatment cleaning is the slow, hands-off cousin. A moss and mould treatment is sprayed on at very low pressure and the weather finishes the job over the following months. It's the usual approach for a roof treatment.
So when someone says "low pressure", it's fair to ask: low compared to what? Here's where the industry draws the lines.
Where the lines sit
- Treatment cleaning: up to 345 kPa, about 50 psi. Sprayed on and left for the weather.
- Soft washing: up to 600 psi, through a large-droplet nozzle. ECIA still counts it as a form of pressure washing.
- Pressure washing: up to 20.7 MPa, about 3,000 psi.
- WorkSafe's asbestos line: water from a pump with an output capability above 350 kPa, about 50 psi, counts as high-pressure water spray. More on that below.
These are the Exterior Cleaning Industry Association's definitions, and its guides measure at the nozzle. They're an industry code, not the law, and they move. The 2023 version of the same code put the soft wash ceiling at 1,500 psi.
Confirm: the soft wash rig you run (pump and nozzle). No pressure goes on this page for it until it's measured at the nozzle.
Sources: ECIA Code of Practice v1.03, ECIA Code of Practice v1.02 (2023) and WorkSafe, asbestos regulations interpretive guidelines
On a painted house, it's no contest.
Aim each one at the same weatherboard wall.
Force does the work.
- Resene says waterblasting doesn't kill moss and mould, so the growth still needs treating anyway.
- It can force water up under weatherboards and gouge timber, Resene says.
- Resene says the pressure varies a lot from machine to machine, and used wrongly a blaster can break windows and lights.
- James Hardie's care guides say don't use a water blaster on its fibre cement cladding.
Chemistry does the work.
- A cleaning solution goes on at low pressure and gets to work on the mould, algae and lichen where they grow.
- It's given time to work, then rinsed off with clean water.
- Far less force on paint, timber and seals. Low-pressure water is what the Hardie and Dulux care guides ask for.
- The catch: it's a chemical, so it has to be mixed, aimed and rinsed properly. How that should go.
Short version: paint, timber, plaster and fibre cement get a soft wash. Plain, hard concrete is where the blaster earns its keep.
Sources: Resene on waterblasting, Resene, exterior timber, James Hardie, Flex Sheet care guide and the Dulux paint care guide
What the makers say.
Paint, cladding and roofing makers publish care guides, and they don't all agree. Some want a blaster kept off their products altogether. NZ Steel allows one within limits, and Resene and Dulux say it has its place on the right surface.
NZ Steel, COLORSTEEL
The odd one out. NZ Steel's maintenance guide says COLORSTEEL roofing and cladding can be washed by hand with water and a sponge or soft nylon brush, or water blasted at no more than 2,900 psi. The steel roofing code of practice allows low-pressure blasting too, with the jet kept away from laps and openings.
For lichen, NZ Steel's own fix is a 2% sodium hypochlorite wash on a soft broom, left 3 to 5 minutes, then washed off with plenty of water. It warns that stronger mixes may harm the coating, and that physically removing lichen can damage the paint film.
It also counts the sheltered bits the rain never reaches, like gutter undersides, soffits and fascias, as "unwashed areas" that need extra hand washing, and makes that a warranty requirement.
So blasting COLORSTEEL isn't banned. It's limited, and the chemistry has to stay inside what NZ Steel recommends. Confirm: your method on steel roofs and cladding
James Hardie
Its Flex Sheet care guide (2025) says wash every 6 to 12 months with low-pressure water and a brush, or every 3 to 4 months in extreme coastal and sea-spray zones. And don't use a water blaster on the cladding. Its Linea weatherboard guide says the same.
Wattyl
Its Forestwood guide says high-pressure water blasting isn't recommended on stained timber. A mild cleaner and a yearly wash instead.
Monier
Strongly advises against pressure washers on its concrete roof tiles, because of the risk of damaging them.
Resene
Says waterblasters suit firmer surfaces like concrete and steel, but the pressure varies a lot, and misused they can break windows and lights. Timber can be damaged and water forced up under weatherboards too. It also says blasting doesn't kill moss and mould, so treat those first. Its own Moss & Mould Killer is a hypochlorite product, and the data sheet lists waterblasting as one way to rinse it off.
Dulux
Its paint care guide says to wash paintwork with low-pressure water, and to use a soft bristle brush on dirt that won't shift. Its House Wash and Prep Wash pages do say to shift very caked-on dirt or mud with a waterblaster before washing. Prep Wash, its mould and mildew wash, must not be mixed with acids, bleach or other cleaners.
Sources: NZ Steel maintenance recommendations, NZ Steel on removing lichen, the NZ Metal Roofing code of practice, James Hardie, Flex Sheet, James Hardie, Linea, Wattyl Forestwood, Monier, maintaining your roof, Resene on waterblasting, Resene Moss & Mould Killer data sheet, the Dulux paint care guide, Dulux House Wash and Dulux Prep Wash
Strong stuff, so it's handled with care.
Many soft wash solutions are based on sodium hypochlorite, the active ingredient in household bleach, usually with a surfactant to help it cling. Some use hydrogen peroxide, or a no-rinse moss treatment instead.
Commercial hypochlorite usually comes at 12.5 to 15% and gets diluted way down on site. For scale, NZ Steel's lichen wash for COLORSTEEL is 2%. In strong form it's corrosive to skin and eyes and toxic to aquatic life, so the handling is the bit that counts. Here's how it should go.
Mixed to the label
Diluted exactly as the label says, with splash goggles and gloves on and the safety data sheet on hand, which WorkSafe requires. Never mixed with acids or ammonia, because that can give off toxic gas. Confirm: the product you use and your usual dilution
Test spot first
A small, out-of-the-way patch gets done first, so any finish that reacts badly shows up there and not across the whole wall. ECIA's guidelines call for it. Confirm: do you test spot on every job?
Garden soaked
Plants along the house get soaked with plain water before and rinsed again after, and nothing gets sprayed if the wind could carry it onto the garden or the neighbour's washing. Confirm: your plant protection routine
Glass kept clear
Solution isn't left to dry on glass or aluminium joinery. Resene says keep its moss and mould killer off both, and ECIA warns that dried solution clouds glass.
Rinsed before it dries
Worked in small sections, out of the hot sun where possible, and rinsed off with clean water before it gets a chance to dry on.
Out of the drains
Wash water isn't meant for the stormwater. ECIA says letting it in is illegal under the RMA, and calls for diverting it onto lawn or other unsealed ground. Confirm: how you keep wash water out of the stormwater
Sources: ECIA best-practice guidelines for claddings and roofs, a sodium hypochlorite 12 to 15% safety data sheet, the Resene Moss & Mould Killer data sheet, WorkSafe on safety data sheets and NZ Steel on removing lichen
Hard concrete? Out comes the blaster.
We're not anti-blaster. On the right surface it's the best tool for the job, and we use one.
Resene says waterblasters suit firmer surfaces like concrete and steel. ECIA's driveway guidance says rotary heads suit heavy-duty cleaning of concrete driveways and masonry, and that the same heads can damage painted surfaces. Right head, right surface.
It's still not full noise on everything hard. Blasting doesn't kill moss, so the growth gets pre-treated first. Too hard a jet, or a nozzle held too close, can knock stones out of exposed aggregate. Blasting pavers set in sand can wash their joints out. And ECIA says asphalt and bitumen driveways shouldn't be pressure washed.
Water restrictions come into it too. In Horowhenua, the higher restriction levels limit commercial water blasting, so a blasting job might have to wait until they lift.
Confirm: that you do blast hard concrete, and your set-up for it, for example a rotary surface cleaner or a fan nozzle
See SurfacesSources: Resene on waterblasting, Resene, cleaning outdoor areas, ECIA guidelines for driveways, Hydroclean on exposed aggregate and Horowhenua District Council, water restrictions
Older home? Asbestos comes first.
This bit isn't a preference. It's the law, and it's why the age of your house matters before anyone picks up a wand.
The rule
Under the asbestos regulations, a business must not use high-pressure water spray or compressed air on asbestos, or anything containing it. WorkSafe's guidelines define high-pressure water spray as water from a pump with an output capability above 350 kPa, about 50 psi, and name water blasters and pressure washers as examples. The exceptions don't cover cleaning.
You can't tell by looking
ECIA's code says Super 6 type roofing profiles, some shingles and older metal tile roofs should be assumed to be asbestos until testing proves otherwise, and its guidelines say asbestos can turn up in properties built before 2000. WorkSafe says find out first, from an asbestos survey, the building plans, the LIM or a tested sample.
Soft washing isn't a free pass
WorkSafe's safety alert names a soft wash or chemical wash as the alternative to blasting. ECIA says soft washing asbestos is illegal too, and that only low-pressure treatment cleaning, under 50 psi, by experienced people can be done. The two don't line up neatly, so a possible asbestos roof is a find-out-first job, not a soft wash job. WorkSafe's info sheets set out cleaning a weathered asbestos roof, even clearing its gutters, as asbestos-related work: respirators, the area isolated, waste bagged as asbestos waste.
Plenty of Kāpiti homes are old enough to ask the question. Going by the dwelling-age table in a council-commissioned housing report, close to half of them were built before 1980 (2019 data).
Lead paint is the other old-house catch. ECIA notes the original paint on homes built before the 1990s is likely to be lead-based, and likely to be in poor condition by now, so only someone who knows how to handle it should clean or strip it.
Our rule: we don't do asbestos work. If a roof or panel is known to contain asbestos, we'll decline the job. If your home was built before 2000 and you'd like a roof treatment, we may ask for an asbestos check first. Confirm: what you do with old, flaking paint that might contain lead
Ask about an older homeSources: WorkSafe, asbestos regulations interpretive guidelines, WorkSafe safety alert on blasting and asbestos, WorkSafe info sheets on weathered asbestos roofing and gutters on asbestos roofs, the ECIA Code of Practice, ECIA best-practice guidelines and the Kāpiti housing demand and need report (2022)
Surface by surface.
Here's where the guidance lands for the surfaces most homes have, and what we'd reach for. Your own maker's care guide is the final word, so dig it out if you've got it.
Painted weatherboards
Pressure can force water up under the boards and damage the timber.
Fibre cement, like Linea
James Hardie says no water blaster on its cladding.
Plaster, texture coat and EIFS
Dryvit's guide for this type of cladding says low pressure, a fan tip and the nozzle kept well back. ECIA says take special care around doors, joinery and windows so water doesn't get in.
Stained timber and cedar
Wattyl says blasting isn't recommended on stained timber, and Resene says cedar is easily damaged by it. A gentle wash does it.
COLORSTEEL roofs and cladding
NZ Steel allows a hand wash or blasting within its limits, and a 2% sodium hypochlorite wash for lichen.
Concrete roof tiles
Monier strongly advises against pressure washers. That's a roof treatment job.
Timber decks
High pressure can splinter and gouge soft timber, and Resene says blasting can leave a deck furry. It says never to blast one unless the maker recommends it.
Plain concrete driveways and paths
Hard and intact, so a blaster suits it, with care, once the moss is pre-treated. Pavers and exposed aggregate get a gentler hand, and asphalt doesn't get blasted.
Anything that might contain asbestos
No high-pressure water, by law. Here's why.
Sources: Resene on waterblasting, James Hardie, Linea, Dryvit, EIFS maintenance, Wattyl Forestwood, Resene, exterior timber, NZ Steel maintenance recommendations, Monier, Suds Wash on decks, Resene, cleaning outdoor areas, ECIA guidelines for claddings and roofs and ECIA guidelines for driveways
Stuff you'll hear that doesn't stack up.
Plenty of claims go round about both methods. We checked these ones against the sources.
"Every maker says no blaster, ever."
Not all of them. NZ Steel allows water blasting COLORSTEEL at up to 2,900 psi, and Resene and Dulux both say a blaster has its place on firm surfaces or caked-on mud. Hardie, Wattyl and Monier do advise against it on their products. It depends what you've got.
"Soft washing is garden-hose pressure."
"Soft wash" isn't one fixed number. ECIA's code defines it as anything up to 600 psi at the nozzle, and counts it as a form of pressure washing. It's gentle next to a blaster, but anyone quoting you a figure should say where they measured it.
"Bleach wrecks COLORSTEEL."
NZ Steel's own lichen fix for COLORSTEEL is a 2% sodium hypochlorite wash, washed off with plenty of water. What it warns against is stronger mixes than that. Strength and a proper rinse matter.
"Soft wash solution is harmless."
Sodium hypochlorite is corrosive in strong form and toxic to aquatic life, and Resene says to keep its moss and mould killer off plants. The Commerce Commission warns that vague green claims are risky for any business. So you won't see a green label from us. We'd rather tell you how it's handled.
"Water blasting a roof is illegal."
As far as we can find, only where asbestos is involved, and there it's a hard no. Otherwise it comes down to the roof. NZ Steel allows it within limits, Monier strongly advises against it on concrete tiles, and ECIA doesn't generally recommend pressure washing roofs.
"One soft wash keeps it clean for five years."
We couldn't find independent evidence for the long numbers going round. Resene says painted houses should be washed every year. How long yours stays clean comes down to shade, damp and the sea air.
Sources: NZ Steel maintenance recommendations, NZ Steel on removing lichen, Resene on waterblasting, Dulux Prep Wash, ECIA Code of Practice v1.03, ECIA best-practice guidelines, a sodium hypochlorite safety data sheet, the Commerce Commission environmental claims guidance, Monier and Resene, maintaining exterior painted surfaces
The questions people actually ask.
Is soft washing better than water blasting?
What pressure does soft washing use?
Is soft washing just bleach?
Will soft washing hurt my plants or paint?
Can you water blast my weatherboards?
Will water blasting void my warranty?
My house is old. Could it have asbestos?
Do you water blast driveways?
Where soft washing comes in.
House Wash
Low-pressure soft wash for the whole outside of the house.
See House WashRoof Treatment
Moss and lichen treated without blasting your roof.
See Roof TreatmentSurfaces
Driveways, paths and decks, each at the pressure it can handle.
See SurfacesRoof & Gutter Combo
A roof treatment and a gutter clean at one combined price.
See the comboLet's get your house juicy.
Tell us where you are and what needs a wash. We'll come back to you with a price.
Rather talk? Call 021 000 0000 or email hello@juicyhousewash.co.nz.
Sweet, it's in.
We'll be in touch with your quote soon.