Soft washing is the right tool when the substrate is delicate, painted wood, stucco, asphalt shingles, screen enclosures and old vinyl. The mix does the work at 100-300 PSI so nothing gets stripped, etched or carved. Most Montreal jobs land between $250 and $700 depending on size, access and how much algae has set in.
Chemistry, not pressure, kills the organism at the cell wall
High-pressure water rinses the surface but leaves the algae and lichen colonies alive on substrate they can re-attach to. Soft washing reverses that, the sodium hypochlorite plus surfactant mix penetrates the biofilm and kills the organism, the surfactant lifts the dead matter, and the low-pressure rinse takes the residue down the grass. Surfaces stay visibly clean for twelve to eighteen months on north walls and longer on south-facing ones.
The technique is the same one we use on house washing, roof cleaning and siding cleaning — only the dwell time and the mix concentration shift. When a substrate cannot take any pressure at all, screen enclosures around pool cages, old painted cedar shingles, weathered stucco, soft wash is the only safe method that gets it actually clean.
Recent work
How a Montreal soft wash runs
Four steps from test patch to dry surface
Test patch and prep
Small test section on an unusual substrate to confirm the mix will not lift colour or finish. Drop-cloths over beds, pre-wet plants, brief you on the access route and the rinse zone.
Apply the mix
Low-pressure downstream injector lays the surfactant and biocide mix bottom-up so it does not streak. Roof work uses a 12V pump at slightly higher concentration for tougher biological growth.
Dwell time
Five to ten minutes per elevation, fifteen on a heavily algae-fouled north wall. The chemistry needs the dwell to do its job, rushing the rinse just dilutes the mix before it kills the organism.
Rinse, walkaround, invoice
Top-down low-pressure rinse, plant beds re-rinsed, drop-cloths lifted, downspouts reopened. Walkaround with you at the end so you can point out anything we missed before the invoice gets sent.
Built for Montreal surfaces
Warm-snap freeze, vinyl oxidation and the asphalt-shingle algae problem
Montreal is hard on exterior surfaces in three specific ways. Warm-snap freeze-thaw drives moisture into hairline cracks in stucco and painted wood — high pressure makes those cracks worse, soft wash works around them. Vinyl siding oxidises in the region sun until the colour goes chalky, soft wash lifts the oxidation without polishing the surface unevenly the way a brush would. Asphalt shingle roofs grow gloeocapsa magma streaks every July, soft wash clears them without dislodging granules the way a 3,000 PSI tip would.
For delicate substrates, soft wash is the only method that gets things actually clean without trading short-term shine for long-term damage. Talk to us about an annual maintenance schedule if you want to keep ahead of the regrowth — the same crew, the same mix, the same dwell, on the calendar before the algae shows up. See the two-visit maintenance program for details.
Written quotesPricing
Annual + as-neededCadence
Montreal Pressure Washing soft washingResult
Soft washing pairs with
Other services where chemistry matters more than pressure
Soft washing is the right method for every substrate where pressure would damage the finish. These services use the same mix, only the dwell and concentration change.
Five questions that come up on most soft-wash quotes.
The working mix is sodium hypochlorite diluted to roughly 1-3% at the wall, combined with a surfactant so the chemistry stays on the surface long enough to do its job. Roof work runs at the higher end, siding at the lower end. Concentration is matched to the substrate and the depth of biological growth, not picked off a shelf.
Yes, with the prep we do. We pre-wet plant beds, drop a tarp over delicate perennials, brief you on which gates to keep pets behind and rinse foliage during and after the wash so the mix never lingers. Keep pets indoors during the application window, by the time we finish the rinse it is safe to come back out.
Twelve to eighteen months on a typical Montreal north-facing wall, longer on south and west walls that get more sun and less moisture. Because the chemistry kills the algae and lichen at the cell wall rather than just rinsing the colour off, regrowth is slow. Annual maintenance washes keep the surface from getting visibly dirty in the first place.
Yes, that streaking is gloeocapsa magma, a cyanobacteria that feeds on limestone filler in asphalt shingles. The same soft-wash chemistry used on siding clears it without lifting granules the way pressure washing would. Most shingle warranties actually require soft-wash rather than pressure, so this is the only roof cleaning method we use on asphalt.
Not the whole time. We do a quick walkaround with you at the start to confirm access, plant cover and any sensitive spots, then most clients run errands while we work. We text when we are an hour from done so you can be back for the walkaround at finish. Payment is invoiced after, you do not need to be there to hand over a cheque.
Montreal soft washing reviews
What clients say after the soft wash
★★★★★4.9· 75 reviews on Google
★★★★★
Crew did a test patch on our painted cedar siding before mixing the rest, which was the reassurance we needed. North wall went from green-streaked to clean and we have not seen the algae come back two summers later. Booked them again for the roof.
A. M.
Montreal · lakefront SE
★★★★★
Asphalt shingle roof had the black streaks down the north slope. The Montreal Pressure Washing crew set up the 12V pump, soft-washed the elevations from the ground and rinsed the gutters out at the same time. No granules in the downspout, just clean shingles.
B. K.
Montreal · Tuxedo Park
★★★★★
Stucco around our garage had years of dust ground in and we were nervous about anyone going near it with a pressure washer. Soft wash was the right call, the finish came back to original colour without any cracking or pitting.
J. H.
Montreal · inner-city
★★★★★
Pool cage was full of algae and we had been told no one would touch it because of the screen. The Montreal Pressure Washing crew used a low-pressure soft wash, no screen damage at all and the deck came up at the same time.
Tell us the substrates, the access notes and which elevations are the priority. A Montreal Pressure Washing estimator follows up within one business day, walks the property and leaves you with a written, itemised quote. Most jobs land in the $250 to $700 range depending on size, height and access.
