Soft washing vs water blasting: which suits your house?

Updated 2026-10-06

For the walls and roof of a house, soft washing is almost always the better choice, and water blasting belongs on concrete, pavers and other hard ground. That’s the short version of what we tell people asking about house washing on the North Shore. The longer version, below, covers why, what a blaster can damage, and the one case where high pressure is against the rules.

What’s the difference between soft washing and water blasting?

The difference is what does the cleaning. Soft washing uses a cleaning solution applied at low pressure, leaves it to kill mould, algae and lichen, then rinses gently. Water blasting uses a narrow, high-pressure jet of water to strip dirt and growth off by force. One relies on chemistry and time, the other on pressure, so each suits very different surfaces.

Think of it as the difference between soaking a pot and scouring it. A soak loosens everything without scratching the surface, while a scourer gets results fast and takes a bit of the surface with it. On concrete that doesn’t matter. On a painted weatherboard or a plaster wall, it does.

There’s also a difference in what’s left behind. A jet can tear the visible green off a wall without killing what’s rooted in the paint or timber, so it comes back. A solution reaches into the texture of the surface and kills the growth where it lives. You can read more about how we use the gentle method on our soft washing page.

When is water blasting the right call?

Water blasting is the right tool for hard, unpainted surfaces that can take the force: concrete driveways and paths, exposed-aggregate patios, pavers, and some bare masonry walls and retaining walls. On these, a high-pressure jet lifts ground-in dirt, moss and slippery algae quickly, often with a surface cleaner attachment that keeps the finish even and stops striping.

Even then, more pressure isn’t always better. Too close a jet can etch the surface of concrete, loosen the sand between pavers and wear the top off exposed aggregate. A good operator matches the nozzle and distance to the surface, and treats stubborn growth with a solution first so the blaster doesn’t have to work as hard.

For driveways, paths and patios, our water blasting service is the one to look at. Many people book it on the same visit as a soft house wash, finishing with the ground so nothing from the walls runs onto clean concrete.

What can water blasting damage on a house?

On a house, a water blaster can strip or lift paint, roughen and split timber fibres, gouge plaster and EIFS coatings, and force water up behind weatherboard laps or past window and door seals. That water can soak framing and linings out of sight. It can also break old putty and seals around joinery, so a short-term clean turns into a repair job.

• Paint: pressure finds any weak edge and peels it back. Once paint has lifted, the timber underneath starts taking on water.
• Timber: softer timber can be furred up by a jet, leaving a rough, hairy surface that holds dirt and doesn’t take paint well.
• Plaster and EIFS: the finish coat is the waterproofing. Chipping or cracking it lets water into the wall.
• Weatherboard laps and flashings: boards are designed to shed water running down, not water driven up from below.
• Windows and doors: seals, putty and weep holes can be pushed past, and water ends up inside.

Consumer NZ’s advice on maintaining exterior walls points people to a soft brush and a low-pressure hose for routine washing, and to the cladding maker for cleaning products. That matches what we see: most damage from washing comes from too much pressure, not too little.

Why asbestos-era roofs must never be water blasted

High-pressure water must never be used on roofing that contains asbestos. WorkSafe says water blasting and compressed air are specifically prohibited on asbestos-containing material under the Asbestos Regulations, because they break the material up and spread fibres across the property. Buildings from before the 2000s may contain it, including some decramastic tile roofs, so older roofs get a low-pressure clean instead.

WorkSafe’s safety alert on high-pressure spraying of roofs describes a 1970s house where a decramastic roof was water blasted. Testing later found chrysotile asbestos in the tiles, debris had spread inside and outside the home, and the property needed specialist remediation. You can’t tell by looking whether a decramastic roof contains asbestos; in that case it took testing to confirm it.

That’s why our roof cleaning uses a soft wash or a spray-and-leave treatment, never a blaster, on any roof that could be from that period. If suspect material turns up partway through a job, the work stops and specialist advice comes first. If you’re not sure of your roof’s age or material, tell us when you ask for a quote and we’ll treat it as suspect until shown otherwise.

Which lasts longer, a soft wash or a water blast?

On walls and roofs, a soft wash generally stays clean longer, because the solution kills mould and lichen rather than just tearing off the visible layer. Blasting leaves roots and spores in the surface, and on paint or timber it can roughen the finish so growth gets a better grip next time. How long either lasts still depends mostly on shade, moisture and salt.

We’d be careful with anyone promising a set number of years. A sunny north wall in a breezy spot might stay clean well over a year after a soft wash, while a south wall under trees can show green within months whatever method is used. On concrete, the same logic applies: a blast followed by a treatment holds up better than a blast alone.

How do the costs compare?

For a typical house, a soft wash and a water blast of the walls cost much the same, because most of the price is time on site, access and set-up. Published Auckland prices for a three-bedroom single-storey soft house wash sit around $300 to $520 incl. GST. Where the two differ is risk: repairing paint or water damage after a blast costs far more.

Hard surfaces are priced by area and condition rather than by bedrooms, and roofs cost more than walls whichever way they’re cleaned, because of the height and safety set-up. The price tables on our house washing and soft washing pages break those bands down, and we confirm the actual figure once we’ve seen the property.