The Damage That Looks Like a Cleaning

Of all the ways a brick building gets damaged, one of the most common is also one of the least expected: someone cleans it. A property owner wants the facade to look fresh, a contractor shows up with a sandblaster or a high-pressure washer, and a day later the building is brighter — and quietly ruined. The damage from aggressive cleaning doesn't show up as a hole or a crack you can point to that afternoon. It shows up over the next several years as accelerated decay, and by then it's permanent.

This is worth understanding before you hire anyone to "clean up" a brick building, because once the harm is done, it can't be undone. You can't put the surface back on a brick. Here's what's actually happening when masonry gets blasted or blasted with water, and what careful cleaning looks like instead.

Brick Has a Skin, and It Only Has One

When brick is manufactured, the firing process creates a hard, dense outer layer — a fired "skin" — on the face of each unit. That skin is the brick's weatherproofing. It's denser and far more water-resistant than the softer, more porous body of the brick underneath. As long as the skin is intact, the brick sheds water and lasts for a century or more.

Sandblasting removes that skin. So does any abrasive media blasting, and so does high enough water pressure. Once you grind or blast the fired face off, you expose the soft, absorbent interior of the brick to the weather. From that point on, the brick drinks in water it used to repel — and in a Chicago-area climate, water in brick means freeze-thaw spalling.

This is the cruel part: a sandblasted wall can look great the day the work is done. The damage is invisible at first. But you've turned a weatherproof surface into a sponge, and the next several winters do the rest. Buildings that were blasted in the 1970s and '80s are some of the worst-deteriorated masonry we work on today, decades later.

What High-Pressure Washing Does

People assume water is gentle. At the pressures often used to "clean" masonry, it isn't. A high-pressure washer can do several kinds of damage at once:

Erodes the mortar joints. Pressure that strips dirt also strips mortar, especially older or softer mortar, opening the joints and driving the building toward needing tuckpointing it didn't need before.
Blasts the brick face in the same way abrasive media does, just with water — wearing down the fired skin on softer brick.
Forces water deep into the wall. This is the one people never think about. High-pressure water doesn't just clean the surface; it drives moisture into the masonry, behind the brick, and into the wall cavity, where it has no easy way out. On a solid masonry wall you've just saturated the structure; on a veneer wall you may have forced water past the flashing.

Pressure washing has its place on some hard, modern surfaces. As a default tool for cleaning an older brick building, it causes more problems than it solves.

Why Historic and Older Brick Is Most at Risk

The older and softer the brick, the worse abrasive cleaning is. The soft-fired common brick used in 19th- and early 20th-century buildings — exactly the kind you see in older Chicago neighborhoods and historic downtowns across the suburbs — has a thinner, more critical fired skin and a softer body underneath. Blasting it is catastrophic. Preservation standards for historic masonry treat abrasive cleaning as off-limits for precisely this reason: the damage is irreversible and it accelerates the loss of irreplaceable historic fabric.

Newer, harder brick is more forgiving, but "more forgiving" is not the same as "fine." The principle holds across the board: the gentlest method that gets the building acceptably clean is the right one.

How Masonry Should Actually Be Cleaned

Careful masonry cleaning starts from the opposite premise of blasting. Instead of "use the most aggressive method and stop when it's clean," the rule is "use the gentlest method that works, and don't chase perfection at the cost of the surface."

In practice that means:

Start with the least aggressive approach — low pressure, water, and appropriate masonry-safe cleaning agents matched to the type of soiling and the type of brick.
Test a small, inconspicuous area first. A responsible contractor proves the method is safe on a patch before touching the whole facade.
Match the cleaner to the stain. Different soiling — atmospheric grime, biological growth, efflorescence, paint — calls for different, specific approaches, not one universal blast.
Accept that an old building can look its age. A century-old wall is not supposed to look like new brick. Trying to force it there is what causes the damage.

Cleaning is also usually a step inside a larger restoration, not a standalone event. If the joints need work, the cleaning and the repointing get planned together so the wall isn't disturbed twice.

Questions to Ask Before You Let Anyone Clean Your Building

What method will you use, and why that one for this brick? If the answer is "we sandblast everything," walk away.
Will you test an inconspicuous area first? The right answer is yes, always.
What pressure will you use on the masonry? Vague or high numbers are a warning sign on older brick.
Have you cleaned buildings like this before? Experience with older and historic masonry specifically is what protects your building.

The Bottom Line

A brick building can be cleaned safely — gently, with the right method tested first, by someone who understands that the fired skin on the brick is the only one it gets. What it can't survive is the fast, aggressive version: sandblasting, abrasive media, or high-pressure water that strips the surface, opens the joints, and saturates the wall. That kind of "cleaning" trades one good afternoon for a decade of accelerated decay.

If you're considering cleaning or restoring a brick building anywhere in Chicagoland and you want it done without damaging the masonry, Emerald Masonry LLC can assess the building and recommend the right approach. We're a family-owned, licensed, bonded, and insured masonry contractor based in Palos Heights with more than 40 years of experience on Chicago-area brick and stone. Contact us for a free on-site evaluation, or call (708) 288-1696.

Why Sandblasting and Power-Washing Ruin Brick — And How Masonry Should Actually Be Cleaned