Guide
Soft washing or pressure washing: which one for your house?
To clean a house, the reflex is to reach for the pressure washer. On a roof or siding, though, that's not always a good idea. Here's the difference, surface by surface.
Soft washing vs. pressure washing: the difference
A pressure washer cleans with the force of the spray. It works well on concrete or a driveway, but on more fragile materials that force can strip, scratch or drive water where it shouldn't go.
Soft washing flips the logic: a cleaning solution is applied at low pressure, works for a few minutes on the organisms (algae, mould, moss, lichen), then everything is rinsed, still at low pressure. The solution does the cleaning, not the pressure.
| Pressure washing | Soft washing | |
|---|---|---|
| What cleans | The force of the spray | The cleaning solution |
| Algae and mould | Stripped from the surface, come back fast | Eliminated down to the root |
| Shingle roof | Risk of stripping the granules | Suitable |
| Vinyl siding | Risk of water getting behind the panels | Suitable |
| Concrete, pavers, driveway | Suitable | Possible, but less useful |
Why pressure damages a roof
An asphalt shingle is covered with mineral granules that protect it from the sun. The spray of a pressure washer strips them off: the roof looks clean, but it has lost part of its protection and will age faster. Water under pressure can also get under the shingle courses. Several manufacturers actually advise against pressure washing their shingles.
The stripped granules end up… in the gutters, which they clog. We often find them during our gutter maintenance visits.
Black streaks, moss, algae: what is what
- Black streaks on the roof: colonies of an alga, Gloeocapsa magma, which feeds on certain components of the shingles. They spread over time, often from the top down.
- Thick green moss: it grows in shaded areas, between the shingles, and holds moisture against the roof.
- Lichen: grey or pale green patches stuck firmly to the surface, typical of shaded and older roofs.
- A green film on the siding: algae, especially on the north side and under trees.
- Black spots on the soffit and fascia: often mould, in damp, poorly ventilated spots.
Surface by surface
Vinyl and aluminum
They clean up well with soft washing. With pressure, the danger is aiming the spray upward, under the panels.
Canexel and fibre cement
These sidings are factory-painted: too much pressure can damage the finish. The gentle method is better.
Brick, stone and stucco
Porous materials, and mortar joints that don't like pressure. They need a case-by-case assessment and a suitable product.
Asphalt shingle roofs
This is where soft washing makes the biggest difference: it removes streaks and moss without stripping the granules. For safety, working on a roof also depends on its pitch.
Doing it yourself: precautions
- Don't climb onto a roof that's wet or covered in moss: it's extremely slippery.
- Never aim a pressure washer upward on siding.
- Protect and wet the plants before applying a cleaning product, and rinse them afterwards.
- Follow the product manufacturer's instructions and precautions, and wear glasses and gloves.
- Close the windows and keep children and pets away.
Our upcoming service
What we offer today: complete gutter maintenance and exterior cleaning of gutters and fascia.
