A guy in Sandy Springs rented a 3,000 PSI washer on a Saturday and cleaned the front of his 1962 brick ranch. He called me that Tuesday because the wall had gone from green-tinged to blotchy orange, and there was a pile of what looked like sand at the base. That pile was the face of his brick. He’d taken it off.
I get two or three of these a year, always in spring, always after a good weekend. The wall usually looks worse a year later than it did the week of the cleaning.
What the pressure actually does
Brick has a fired outer skin that’s harder and less absorbent than the body behind it. That skin is thin — on some older brick it’s barely a sixteenth of an inch. Hit it with a narrow tip at high pressure and you erode it, especially on the softer brick common in mid-century tract work around here.
Once that face is gone, the brick drinks. It picks up water faster, holds it longer, and pushes salts to the surface as it dries. That’s why the wall goes blotchy — you’re not seeing dirt anymore, you’re seeing uneven absorption. And in a climate that swings between soaking humidity and hard afternoon sun, a brick that stays wet longer is a brick that spalls sooner.
Mortar takes it worse than the brick does. Older lime-rich joints will wash out a quarter inch deep in one pass without the operator noticing, and now you’ve bought yourself repointing.
What the green stuff actually is
Most of what people are washing off in Georgia isn’t dirt. It’s algae and mildew growing on a north or shaded elevation that stays damp. Blasting it removes what’s visible and leaves the spores, which is why it’s back in eighteen months looking the same.
The thing that keeps it off is drying, not cleaning. Cut back the shrubs that are holding the wall in shade and moisture — I usually ask for eighteen inches of clearance minimum. Fix the downspout that’s misting the corner. Get the sprinkler head that’s been hitting the wall twice a day pointed somewhere else. Those three things do more for a shaded elevation than any washer.
How I clean brick when it needs it
Low pressure and chemistry, in that order. For biological growth, a dilute detergent or a proprietary masonry cleaner, applied to a pre-wet wall, given time to work, then rinsed at garden-hose pressure or a washer well under 500 PSI with a wide fan tip held back a couple of feet.
Pre-wetting matters more than people think. A dry brick pulls the cleaner deep into itself and you’ll never fully rinse it out — that’s how you get the chemical burn look weeks later.
Two things I don’t do on residential brick: muriatic acid straight out of the jug, and anything at all before testing a patch somewhere that doesn’t face the street. I’ve written out how far you can push cleaning before it does harm if you want the longer version. The National Park Service’s preservation briefs on cleaning and water-repellent treatments for masonry are written for historic buildings but the chemistry applies to a 1960s ranch just the same.
What it costs either way
A careful low-pressure chemical cleaning on a typical single-story elevation runs about $0.35 to $0.90 per square foot, so most front elevations land somewhere between $400 and $1,200 depending on access and how much growth there is.
Repointing brick that got washed out is $18 to $35 per linear foot of joint. Replacing spalled brick — which means finding a match for a fifty-year-old unit — is $900 to $2,500 for a small area, and the match is rarely perfect. The cleaning that caused it saved a few hundred dollars.
If the wall is old, soft, or painted, get someone to look at it before anything gets sprayed. Plenty of masonry contractors in Atlanta will do a walk-around and tell you honestly whether it needs cleaning at all. Half the time the answer is trim the bushes and wait a season.
Frequently asked questions
What PSI is safe for cleaning brick? Under 500 PSI with a wide fan tip, held at least a foot back, and only after the wall has been pre-wet and treated. Consumer washers run 2,000 to 3,000 PSI, which is enough to erode the fired face of the brick and cut out mortar joints.
Will the orange blotches go away? Not by cleaning them again. Blotchy color after a washing is uneven absorption in brick that lost its face, plus salts moving to the surface. It fades unevenly over a few years and the only real correction is a mineral coating or replacement.
How often should brick be cleaned? Most brick never needs it. If growth keeps coming back on a shaded wall, the problem is moisture and sunlight, not dirt — fix the drainage and cut back the plantings and you may not clean it again for a decade.