Home → Exterior Cleaning Advice → Soft Wash vs Pressure Wash
Match the method to the surface, not to how dirty it looks. Hard, non-porous, structural surfaces — concrete, pavers, brickwork, hard stands — take pressure. Painted, coated and fragile surfaces — render, paint, weatherboard, Colorbond walls and sheds — take a soft wash, which is a treatment applied at about garden-hose pressure that kills the growth rather than blasting it off. Putting a pressure wand on that second group is the single most common and most expensive mistake in this trade. Roofs sit in between: most get a soft wash, and roofs that suit it get a high-pressure surface cleaner with careful pressure control. Windows get pure water, and solar panels get a soft brush with a mild solar-safe cleaner where needed.
Pressure cleaning is exactly what it sounds like: water delivered with enough force to physically lift material off a surface. On a driveway that is the right tool, and a rotary surface cleaner does it evenly instead of leaving the wand stripes you get from waving a lance around.
Soft washing is a different approach entirely. A cleaning solution is applied to the surface, given time to work, and then rinsed at low pressure. The chemistry does the job; the water only carries it on and washes it off. To a bystander it looks almost lazy compared with a pressure washer. The results say otherwise.
The green on a Toowoomba wall is a living colony — algae, mould, and on older surfaces lichen, which grips into the surface rather than sitting on it. A pressure wand removes the visible part and leaves the root structure. It looks spectacular on the day and greens up again within a season, because you have pruned it rather than killed it.
Meanwhile the wand itself does real damage. On render it drives water behind the surface and can take the texture coat off. On paint it lifts the film and finds every hairline crack. On a tile roof, waved around by hand, it strips the glaze unevenly, which leaves the tile more porous and rougher than it was — so it holds more water and grows moss faster than before it was cleaned. On weatherboard it forces water up under the laps. And on any roof it can push water past the flashings into the ceiling cavity, which is a problem you find out about weeks later.
The giveaway on a badly pressure-washed roof is that the ridge capping mortar has been cut back and the tiles look chalky. That is not clean. That is surface loss.
Ask what the surface is made of, not how bad it looks.
This is where the difference shows up in money rather than appearance. A pressure-blasted wall is green again in a season or two because the colony was never killed. A properly soft-washed wall in Toowoomba holds for two to three years, and a soft-washed tile roof holds for four to six, because the lichen was killed right through and has to re-establish from nothing.
One thing worth expecting on a soft-washed roof: it does not look finished on the day. The treatment kills the lichen on contact, but the dead grey crust weathers off over the following weeks of rain and wind. Anyone promising a soft-washed tile roof that looks brand new by knock-off time is overselling.
Plants and garden beds along the wall line wet down before anything is applied and rinsed again afterwards. Downpipes into a rainwater tank diverted before roof work and reconnected before we leave. Surfaces rinsed properly rather than left to dry with residue on them. And the order right on a whole-house job: roof first, then gutters, then walls, then windows — because every one of those steps drops material onto the next.
Send us a photo. We will tell you which method the surface takes and why, and give you a firm price before we start — $20 million public liability, Working at Heights certified, no travel surcharge within about 35km of Toowoomba.
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