A pressure washer is the cheapest tool that shows up on an exterior repaint and the only one capable of damaging a house in a single afternoon. It is also the step most often described in two words on a bid, which is unfortunate, because the wash decides whether the coating that follows is bonded to the building or bonded to a layer of dirt lying on top of it.
The wash has a narrow job, and most of the trouble comes from expecting more of it. It is not a restoration, it is not a substitute for scraping, and it is not a cleaning service with paint attached. It exists to remove the loose material sitting between the new coating and the sound old surface, and then to leave the wall dry enough to prime. Everything else people hope it will do is either a different step or wishful thinking.
Four things come off with water, and on a house near the harbour they are the four that count. Flaking and lifting paint, which a stream finds faster than any scraper will. Mildew and algae, provided a biocide does the killing and the water only does the rinsing. The thin salt film that settles continuously on every exterior surface within a mile or two of the water, which is invisible, holds moisture against the substrate and breaks adhesion quietly. And light surface powder.
That last one is where expectations usually break down. Water lifts what sits on a surface, not what the surface has turned into, and chalking is the clearest case of the difference. A faint dusting rinses away and leaves sound film behind. A wall that is still producing powder after it has washed and dried has a degraded binder several layers deep, and the answer to that is a penetrating masonry conditioner or a chalk binding primer, not more pressure. Turning the pressure up at that point starts removing the old coating instead, which converts a repaint into a strip job nobody quoted.
What water will never touch
Grease and cooking film around a kitchen vent, exhaust residue on a wall facing a carport, and silicone overspray from an earlier repair are all hydrophobic. Rinsing them spreads them thinner and wider. Those areas need a degreasing detergent, agitation with a brush, and a separate rinse, and they are small enough that doing it by hand is faster than arguing with a wand.
Rust bleed from fasteners and tannin stains from redwood or cedar are not surface contamination at all. They are something migrating out of the material, and they come back through two topcoats unless a stain blocking primer goes over them.
Sound glossy paint is untouched by water as well. Gloss is a bond problem, not a cleanliness problem, and it is answered by sanding to dull it or by a bonding primer.
White crystalline bloom on stucco is the one case where washing makes things actively worse. Those are soluble salts that came out of the wall, and flooding them dissolves them and sends them back in to reappear later. They get brushed off dry.
The damage a careless wash does
Cement plaster holds a surprising volume of water, and it has hairline cracks whether or not anyone can see them from the ground. A close, high pressure stream drives water straight through those cracks, and worse, up under the weep screed at the base of the wall and into the joint where plaster meets window trim. None of that shows on the day. It shows the following summer as blisters on an elevation that was prepared perfectly in every visible respect.
Lap siding and shingles have the same vulnerability with a simpler rule attached: never spray upward into a lap. Water that gets behind a board has no reason to leave, and it pushes the new coating off from the back months later.
Old window glazing putty, already dried and shrunken on a house of any age, is blown out of the rabbet by a near stream, and the same pass forces water past the sash and onto interior sills. Weep holes in aluminium window frames are drainage paths, and flushing them at high pressure sends water into the wall cavity rather than out of it.
Soft woods take physical damage that is permanent. Fir fascia, cedar trim and redwood siding raise their grain and fur up under too much pressure, and the resulting fuzzy surface holds paint worse than the dirty wood did. Etching on siding reads as a faint washboard pattern that becomes obvious once a fresh coat of gloss goes over it and raking afternoon light hits the wall.
On a house built before the late nineteen seventies, pressure washing old paint is uncontained paint removal. Chips and dust go into the soil, into the planting beds, and over the property line, which on the close-set lots common across much of Long Beach means into somebody else's yard. Lead safe work practices exist for exactly this, and a crew that intends to blast a pre-war bungalow should be asked how containment is handled before anything is switched on.
Pressure, volume and nozzle
Pressure dislodges, water volume carries debris away, and distance from the surface does more than either dial. Halving the distance between the tip and the wall multiplies the force landing on it, so a technician working close at a modest setting is hitting the house harder than one standing back with the machine wide open.
House washing generally lives in the low hundreds to around one thousand pounds per square inch at the surface, with a fan tip of twenty five to forty degrees and the wand held well back and angled slightly downward. The zero degree tip, usually red, has no use on a building at all. It belongs to concrete and even there it leaves marks.
The honest way to settle any of this is a test patch on an inconspicuous elevation, inspected close up before the rest of the house is committed. If the test leaves raised grain, a bright etched stripe or fresh exposed substrate, the setting is wrong and the test just saved the job.
Soft washing, and when it is the right call
A soft wash runs at garden hose pressure and lets chemistry do the work: a dilute hypochlorite solution with a surfactant, applied, left to dwell, then rinsed. It kills mildew rather than relocating it, and it is the correct method on old wood siding, on anything fragile, on heavily organic north facing walls, and on any surface where mechanical force is the risk rather than the solution.
The trade is housekeeping. Plants get soaked with clean water before and rinsed again after, metal gets rinsed properly because the solution is corrosive, and the runoff path matters. A crew that treats a soft wash as spray and walk away produces dead shrubs and streaked windows.
The shaded wall, and the dry time nobody budgets
A north elevation under a deep eave in Long Beach can sit damp for most of the cool half of the year, and the marine layer gives it a wet and dry cycle every night. Mildew on that wall is not a dirt problem, it is a habitat problem, and it grows straight through a new coating if it was rinsed rather than killed. The wash there needs a mildewcide with real dwell time, a thorough rinse, and realistically a mildewcide additive or a coating rated for biological resistance going on afterward. Cutting back the shrub holding the damp against the wall does more good than any amount of extra pressure.
Dry time is the line most schedules quietly skip. Stucco and masonry hold water millimetres deep and look dry long before they are. Wood should be metered and should read comfortably below the high teens as a percentage. In warm dry conditions a washed wall may be ready the next day. On a shaded elevation during a fog cycle it may need two or three, and primer applied before then seals moisture under the film and blisters it later.
The practical answer is to wash elevation by elevation, a day or more ahead of the crew, rather than washing the whole house on a Monday and chasing it with primer. Each wall then gets its own drying window instead of sharing one average.
What gets covered, closed and moved
Exterior outlets and fixtures get taped or plugged and the circuits killed at the panel. Light fixtures get bagged. Windows and doors get checked for gaps rather than assumed closed, and anything with a known leak gets taped from outside. Dryer vents, attic vents and skylights get covered, not sprayed into.
The air conditioning condenser gets wrapped. Plants get wet down first and rinsed afterward. Cars go off the driveway, and on a narrow street the car parked three feet away belongs to a neighbour who would rather be asked than surprised. Overspray from a wash carries further than people expect, and so does the smell of hypochlorite.
When a wash is the wrong tool entirely
Sometimes the right call is to leave the machine on the truck. A heavily failing wall is better dry scraped first, so the water is not driving a thousand paint chips into the garden. A small greasy or chalky area is better hand scrubbed with a brush and a bucket. A chalked surface that keeps powdering needs a conditioner, and no wash will substitute for it. And a wall with active water intrusion, the kind announcing itself with salt bloom or blisters in one isolated patch, needs the source found before anything is cleaned or coated, because washing it adds water to a wall that already has too much.
Judging whether the wash was done well takes about ten minutes before primer day. Run a hand over the walls and look for powder. Check the shaded elevations for any remaining dark spotting. Look along the siding and the fascia under low light for etching or raised grain. Look at the interior sills under the windows for water that came in. Push on the soft wood near the ground. If all of that reads clean and the wall is genuinely dry, the most underrated step on the job has been done properly, and the coating going over it has been given a real chance to last.