Nearly every ruined stucco wall we see was ruined by pressure, not dirt. A traditional wall puts about an eighth of an inch of finish coat between you and its guts. EIFS puts less. A 3,000 PSI wand removes that in under a second, and no patch ever blends. Chemistry and dwell time do the work instead.
A traditional three-coat wall is roughly 7/8 inch total: a 3/8-inch scratch coat, a 3/8-inch brown coat, and a finish coat about 1/8 inch thick that carries every bit of the color and texture. That finish coat is the only thing you are cleaning, and it is bound sand. A 15-degree tip at 3,000 PSI held six inches off the wall strips it faster than the operator can react, and because the wand is moving, the damage lands as stripes: lap marks, zebra lines, and clean halos where somebody paused to answer a phone. On sound cement stucco, cap it at roughly 1,500 PSI through a 40-degree fan tip held 18 to 24 inches back. Better answer: skip pressure entirely. Garden-hose pressure, about 40 to 60 PSI, with 8 to 12 minutes of dwell, cleans deeper and risks nothing.
Before anyone sprays, find out whether the wall is cement stucco or EIFS, the synthetic system built over foam board. Knuckle-tap it at chest height in several spots. Cement stucco over lath sounds solid and dead. EIFS sounds hollow and drummy and gives slightly under a thumbnail. EIFS carries roughly 1/16 inch of base coat and 1/16 inch of acrylic finish over expanded polystyrene, so about an eighth of an inch stands between a wand and a permanent hole in the foam. Pressure that merely scars cement stucco punches clean through EIFS. Cap it at 500 PSI, and realistically, keep a pressure washer off it altogether. One-coat stucco, common on Treasure Valley builds since the early 2000s, sits in between at 3/8 to 1/2 inch over foam: tougher than EIFS, far thinner than three-coat.
The damage you cannot see costs more than the damage you can. Stucco is a reservoir cladding. It absorbs water on purpose and dries outward, and a building paper or house-wrap barrier behind it handles whatever gets through. That system only works top-down. Spraying upward drives water under the horizontal laps of the barrier, behind window head flashing, into control joints, and up into the weep screed at the base of the wall, which exists to let water out and not in. Keep the wand level or angled slightly down. Never spray into the underside of a soffit, a frieze board, or a weep screed. Water that gets behind stucco does not show up that day. It surfaces six to eighteen months later as rust bleed streaking down from the metal lath, bubbling paint, or a soft spot under a window.
Acid is the fastest way to destroy a wall permanently. Muriatic acid and hydrofluoric rust removers dissolve the cement paste holding stucco's sand together. You get a bleached patch with loose grit under your palm, and nothing brings it back. Sodium hypochlorite is the correct tool for organic growth, but the errors repeat: mixed too hot, and allowed to dry. Roughly 1 to 2 percent at the wall is plenty for a house wash. Anything that flashes dry on stucco leaves a pale halo harder to remove than the algae was. Keep the surface wet the whole dwell, rinse from the bottom up so dirty runoff never tracks across clean stucco, then rinse again. Integral-color finishes in dark browns and reds, and dark elastomeric paint, can lighten. Test a two-foot square behind a downspout and judge it dry.
Temperature ruins more stucco jobs in Idaho than technique does. Stucco holds water in its pores for hours after a wash. If the overnight low drops below 32°F, that water expands about 9 percent and pops the finish off in flakes along the wall's coldest face. In the Treasure Valley the last spring freeze usually lands early-to-mid May and the first fall freeze early-to-mid October, so the safe wash window runs roughly mid-May through late September. The hot end is worse than people expect. At 95 to 100°F in July, solution flashes dry on a sunlit wall in about two minutes, long before it has done anything, and streaks are the result. Chase shade, or start at 7 a.m. New stucco is its own rule: no washing for at least 28 days, and 60 is better.
This part costs us work. Most Treasure Valley stucco is not dirty in a way a house wash fixes. Humidity here is low, organic growth is slow, and the real staining is mineral, driven by irrigation overspray on 10 to 13 grain water, plus ag and construction dust on the windward wall. Sodium hypochlorite does nothing to mineral scale. If the stain is a chalky white band four feet up on the sprinkler side, move the head; do not buy a wash. Efflorescence is the same trap, since it is salt pushed out by water moving through the wall, so scrubbing treats a symptom. If it returns within one season, you need a stucco contractor. Hosing the bottom four feet with a soft brush is a fine Saturday DIY. When a full wash is genuinely due, soft-wash house washing runs $0.18 per square foot.
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On sound, cured cement stucco, cap it around 1,500 PSI with a 40-degree fan tip held 18 to 24 inches off the wall, and never stop moving. On EIFS or any foam-backed system, 500 PSI is the ceiling. The better answer is that stucco does not need pressure at all. A soft wash at garden-hose pressure with 8 to 12 minutes of dwell cleans further and cannot carve the finish.
You can, and you should not. EIFS is roughly 1/16 inch of base coat plus 1/16 inch of acrylic finish over expanded polystyrene foam, so about an eighth of an inch stands between the wand and a permanent hole. Knuckle-tap the wall first: hollow and drummy means EIFS, solid and dead means cement stucco over lath. Clean EIFS with low-pressure chemistry and a gentle rinse, keeping water out of joints and terminations.
It can. At house-wash strength, roughly 1 to 2 percent sodium hypochlorite, most cementitious finishes handle it fine. Integral-color finishes in dark browns, reds, and tans, plus dark elastomeric paint, can lighten noticeably. Hypochlorite left to dry on any stucco leaves a pale halo that is harder to correct than the algae was. Test a two-foot square somewhere hidden, let it dry completely, and look at it in daylight before committing to an elevation.
Give it 28 days minimum, and 60 if the schedule allows. Portland cement plaster reaches most of its strength near 28 days, and green stucco is soft enough that even moderate pressure lifts sand out of the finish. New walls also push efflorescence for the first several months, which is normal salt migration rather than dirt, so washing it off early usually just invites it back. Construction slurry on glass is the exception: rinse that immediately, because it etches within days.
Not invisibly. Once a wand has removed finish-coat texture, the fix is refinishing, not spot repair, because a patch on textured stucco never matches the surrounding sand, float pattern, and color, and it reads worse in raking evening light than the burn did. Patching runs roughly $8 to $15 per square foot, an elastomeric recoat of a full elevation about $2.50 to $5.00, and a full re-stucco $8 to $12. No one can clean a burn out.
House first, glass second, every time. House-wash runoff carries dissolved dirt and hard-water minerals across the panes and dries into spotting, so cleaning glass first wastes the work. Reflekt sequences it that way and finishes the glass with 100% pure deionized water and no soap, which leaves nothing behind to re-spot. If a crew wants to do the windows first and rinse the walls afterward, ask why.
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