Building Exterior Cleaning: Pressure Washing and Facade Care

Pressure is a tool, not a service. What a facade needs is the removal of a specific soil, and soils differ.

Atmospheric grime, the general grey film that accumulates from traffic and airborne particulate, is a surface deposit. It responds to detergent, dwell time, and a rinse, and needs very little force.

Biological growth, the green and black staining on north-facing and shaded elevations, is alive. Blasting it removes what is visible and leaves what is rooted, which is why a pressure-washed north wall often looks worse again within a season. It responds to appropriate chemistry with dwell time, then a low-pressure rinse.

Mineral deposits, efflorescence on masonry and the white bloom left by hard water, are chemical rather than particulate. Force does nothing useful; the right treatment does.

Salt and road spray on lower elevations, which is an Ottawa constant, is a dissolved deposit. It rinses off readily with water volume and does not need pressure at all.

Naming the soil first is what makes the method obvious. Reaching for the highest pressure available is what turns a cleaning job into a repointing job.

Brick and mortar. The brick face itself is tough; the mortar joints are not. High pressure erodes mortar, drives water into the wall, and on older buildings can remove joint material outright. Masonry is a low-pressure, correct-chemistry, adequate-dwell-time job. On a heritage or soft-fired brick building it is a specialist job, and a general contractor should say so rather than proceed.

Precast and poured concrete. More tolerant than brick, but the same principle applies: too much pressure exposes aggregate and creates a rough surface that then holds dirt faster than before. A cleaned panel that gets dirty twice as quickly has been damaged, not cleaned.

EIFS and synthetic stucco. This is the substrate that gets destroyed most often. The finish coat is thin and the system depends on staying dry inside. High pressure cuts through the coat and drives water into the assembly. EIFS is a soft-wash surface, always.

Metal panel and composite cladding. The metal takes pressure; the coating and the joints do not. Water forced up behind a panel or into a sealed joint is the failure mode here, so the direction of the spray matters as much as its pressure. Work down and away from joints rather than up into them.

Glass and curtain wall. Cleaned as glass, not as facade. Detergent, agitation, and a controlled rinse, with attention to the frames and gaskets that hold water and then streak the glass on the next rain. Our exterior window cleaning frequency guide covers how often this is worth doing on a commercial building.

Wood and painted surfaces. Low pressure and mild chemistry, because both the coating and the substrate beneath it are what you are trying to keep.

Soft washing means applying a cleaning solution at low pressure, allowing it the dwell time it needs to work, then rinsing at a pressure the surface tolerates. The work is done by chemistry and time rather than by force.

It is the correct method for anything living, because it treats the growth rather than merely removing its visible layer. It is the correct method for EIFS, for older masonry, and for any surface where driving water into the assembly is the risk. And it is usually the correct method for large uniform elevations of atmospheric grime, because it covers area faster than a wand can.

Pressure still has its place: hard horizontal surfaces such as sidewalks, loading docks, entry aprons, and parking aprons, where the substrate is robust and the soil is ground in. The mistake is not using pressure, it is using the sidewalk setting on the wall above it.

Exterior work runs top down, for the obvious reason that anything released above lands on everything below. That means the elevation is cleaned before the entrance canopy, the canopy before the sidewalk, and the sidewalk last.

Protection comes before any of it. Landscaping, light fixtures, signage, air intakes, electrical, and any opening in the wall need covering or isolating before the first drop of solution is applied. Air intakes matter more than most people expect, because pulling a cleaning solution into a building's ventilation is the fastest way to turn an exterior job into an indoor complaint.

Runoff is the other constraint. Everything washed off a facade lands on the ground and travels to a drain. Where the solution or the soil warrants it, the runoff is contained and recovered rather than allowed into a storm system, and the property's own requirements decide which. As with any wash job, the question is answered at the walkthrough, not on the day.

Access decides feasibility. Ground-level and low-rise elevations are reachable from the ground or a lift. Above that, the work becomes a rope-access or suspended-platform job with its own planning, and it usually makes sense to combine it with the window cleaning cycle rather than mobilising twice. Our high-rise building cleaning guide covers how the elevations, glass, and interior circulation fit into one schedule.

The window for exterior washing in this climate is genuinely narrow, and pretending otherwise produces ice and disappointment.

Wet exterior work needs temperatures reliably above freezing for the duration of the wash and the drying that follows, which in practice means late spring through early autumn. Washing a wall in shoulder season and leaving water in a masonry joint overnight, where it freezes and expands, is a way to cause the damage the cleaning was meant to prevent.

That gives most Ottawa buildings one natural slot: late spring, after the salt season has ended and the road spray on the lower elevations has stopped accumulating. A second pass in early autumn suits buildings with heavy biological growth or a high-visibility entrance.

Within the season, the weather on the day still matters. Direct sun on a hot elevation dries a solution before it has had its dwell time, which is why crews work the shaded side or start early. Wind carries overspray onto cars, windows, and neighbouring property. Rain within a few hours of a job can undo a rinse that has not yet dried.

A quote worth comparing names the elevations, the substrates, the method for each, and the ground-level work.

Elevations, because "the building" is not a scope. North and shaded elevations often need different treatment from the sunny sides, and the street-facing elevation may deserve a frequency the back does not.

Substrates, because the method follows from them. A quote that does not name whether a wall is brick, precast, or EIFS has not made the decision that matters.

Ground-level work, because the entrance is what people actually see: the canopy, the door surround, the sidewalk, the entry apron, the bollards and bin enclosures. These take the most soil and are the cheapest part of the job to include.

Protection and runoff, because both are real costs and both are what a low bid quietly leaves out.

Our commercial janitorial services in Ottawa scope exterior work this way, elevation by elevation with the method named against each substrate, so the comparison between two quotes is a comparison of the same job.

If a building only gets one exterior job a year, it should be the bottom three metres.

That band takes everything: road spray and salt thrown up by traffic through the winter, hand contact on doors and glass, litter and food soil around bins and smoking areas, gum on the sidewalk, and the grime that collects wherever people stand still. It is also the only part of the building most visitors ever see closely.

The entrance is the highest-value square metre on the site. The door surround, the glass, the frame, the canopy soffit, the mat well, and the two metres of sidewalk in front of the door together form the impression a visitor forms before they are inside. Cleaning them properly is inexpensive and the effect is immediate.

Sidewalks and entry aprons are the one place where genuine pressure is the right tool, because the substrate is robust and the soil is ground into it. Gum, oil drips from the loading area, and the dark traffic path down the middle of a walkway all need force and heat rather than chemistry and patience.

Bin enclosures, bollards, and the loading dock are the parts nobody quotes and everybody notices. They collect the worst soil on the site and they are usually adjacent to a drain, which makes them the one area where runoff control needs the most attention.

Salt is the seasonal driver here as it is everywhere else in an Ottawa building. The lower elevations accumulate a road-spray film through the winter that dulls glass, stains masonry, and etches metal over time. Removing it in a late-spring pass, rather than letting it sit through a second season, is most of what keeps a ground floor looking maintained.

Almost every commercial exterior job happens while the building is occupied, and the plan for that is part of the scope rather than an afterthought.

Pedestrian routing comes first. A wet sidewalk under a wall being washed is a hazard, so the crew needs an agreed alternate route, signage, and a working area that moves with them rather than closing the whole frontage for a day.

Parking and vehicles come second. Overspray on cars is the most common complaint from exterior work, and it is entirely preventable with notice, a temporarily cleared row, and attention to wind direction.

Tenant notice comes third. Occupants need to know which elevation is being worked, when windows should stay closed, and when the air intakes will be isolated. A short notice a few days ahead prevents most of the calls a facade job generates.

Timing is the last piece. Early mornings suit the entrance and any elevation in direct afternoon sun. Weekends suit the loading area and the frontage of a retail tenant. A building with a night shift may have no quiet window at all, which is worth knowing before the schedule is written rather than after.

• Step 1. Identify the substrate on every elevation: brick, precast, EIFS, metal panel, glass, wood, painted. Write it down. Every later decision follows from this list.
• Step 2. Name the soil on each elevation: atmospheric grime, biological growth, mineral deposit, road salt, or a combination. The soil, not the surface, decides the chemistry.
• Step 3. Choose the method per elevation and record it: soft wash for living growth, EIFS, and older masonry; pressure only on robust horizontal surfaces.
• Step 4. Protect before you start: landscaping, fixtures, signage, electrical, openings, and above all air intakes.
• Step 5. Confirm where runoff goes and what the property requires, and set up containment and recovery where the solution or the soil calls for it.
• Step 6. Work top down: elevation, then canopy, then sidewalk and entry apron.
• Step 7. Allow the solution its dwell time. Work shaded elevations or early hours so a hot wall does not dry the product before it has worked.
• Step 8. Book inside the season: reliably above freezing through the wash and the drying, which in Ottawa means late spring to early autumn.
• Step 9. Combine the facade with the window cycle where access equipment is involved, so the building is mobilised once rather than twice.

Is pressure washing safe for a brick building?

Not at high pressure. Brick faces tolerate more than mortar joints do, and eroded mortar and water driven into the wall are the two failure modes. Masonry is a low-pressure job with the right chemistry and enough dwell time, and older or soft-fired brick is specialist work.

What is the difference between soft washing and pressure washing?

Soft washing applies a cleaning solution at low pressure, gives it time to work, and rinses at a pressure the surface tolerates. Pressure washing relies on force. Soft washing is correct for anything living, for EIFS, and for older masonry; pressure suits robust horizontal surfaces such as sidewalks and loading docks.

Why does the green staining come back so quickly after a wash?

Because it is alive and only the visible layer was removed. High pressure takes off the surface growth and leaves what is rooted in the substrate, so it regrows. Treating it with appropriate chemistry and dwell time is what actually clears it.

When can a building exterior be washed in Ottawa?

Between late spring and early autumn, when temperatures stay reliably above freezing through the wash and the drying that follows. Washing in shoulder season risks water freezing in masonry joints overnight, which causes exactly the damage the cleaning was meant to prevent.

How often should a commercial building exterior be cleaned?

Most commercial buildings suit an annual wash in late spring, with a second pass in early autumn for buildings with heavy shaded growth or a high-traffic entrance. Ground-level work such as the entrance, canopy, and sidewalk usually deserves a higher frequency than the elevations above it.

Should facade cleaning and window cleaning be booked together?

Where access equipment is involved, almost always. Mobilising a lift, platform, or rope access once for both is cheaper than twice, and it avoids washing a facade above glass that was cleaned the week before.

Exterior cleaning goes wrong in one specific way: the method is chosen before the surface is identified. Write down the substrate and the soil for every elevation, pick the method from that rather than from the equipment on the truck, protect what is below and behind the wall before starting, and book inside the season this climate actually allows. Questions about the condition of a facade, a joint, or a cladding system belong to the engineer or envelope consultant responsible for it. Cleaning's job is to remove what has landed on the building without adding to what has to be repaired.