The fastest way to ruin good brick is to clean it too aggressively. I learned that reporting on a restoration where an eager homeowner had rented a pressure washer, blasted their front steps, and stripped the face right off century-old brick — along with half the mortar joints. Brick and mortar are more fragile than they look, and the mortar is almost always the weaker of the two. Clean with that in mind and you’ll do fine.
Start with the gentlest thing that works
The guiding principle professional conservators use is simple: start with the gentlest method and escalate only if you have to. The National Park Service’s preservation guidance on cleaning historic masonry is built entirely around that idea, and it applies just as well to a 1990s house as to a historic one. In practice that means low pressure and mild detergent before anything harsh, and a test patch in an inconspicuous spot before you touch the visible face.
Why pressure washing is so risky
A pressure washer that will happily clean a concrete driveway can carve mortar out of joints and erode the hard outer skin of the brick, exposing the softer, more absorbent core underneath. Once that skin is gone the brick soaks up water and deteriorates faster — you’ve traded a cosmetic problem for a structural one. If you must use a washer, keep it under about 400 to 800 psi, use a wide fan tip, and stay well back. Most pros I know reach for a garden hose and a soft brush first, and are surprised how often that’s enough.
Match the cleaner to the stain
- General grime: water, a mild dish soap or masonry detergent, and a natural- or nylon-bristle brush. Never a wire brush — it burnishes and scratches.
- Efflorescence (white powder): usually brushes off dry, or comes off with plain water. Resist the urge to hit it with acid; it typically returns until the moisture source is fixed.
- Biological growth (green or black): a diluted, masonry-safe cleaner or a mild bleach solution, well rinsed. Let it dwell, don’t scrub it dry.
- Smoke or heavy staining: a proprietary masonry cleaner made for the job, following the label’s dwell time.
About acid
Muriatic (hydrochloric) acid is the tool people reach for and misuse most. It can etch brick, burn out lime mortar, discolor the surface, and leave salts behind that cause fresh efflorescence. If a job truly calls for a masonry acid, it’s diluted, the wall is soaked with water first so the acid can’t penetrate deep, dwell time is short, and everything gets flushed thoroughly. Honestly, this is the point where I tell most homeowners to hire out — the downside of getting it wrong is permanent.
Protect the mortar and finish clean
Soft lime mortar on older brick is especially vulnerable; it’s meant to be sacrificial and it erodes easily. If joints are already crumbling, cleaning can accelerate the loss, so repoint after cleaning, not before. Rinse from the top down and keep the wall wet ahead of any cleaner so it doesn’t wick in. And resist the reflex to seal right afterward — sealing can trap moisture and cause more harm than good, which is a whole discussion of its own in when sealing brick and stone helps and when it hurts.
What it costs
DIY cleaning of a small area is mostly your time and $30 to $100 in supplies. Professional masonry cleaning typically runs $2 to $6 per square foot, more for delicate historic restoration or heavy staining. That’s cheap insurance compared with re-facing brick you scoured the skin off.
Frequently asked questions
Can I pressure wash brick? Only carefully. High pressure erodes mortar joints and the brick’s hard outer skin. Keep it under roughly 400 to 800 psi with a wide tip, or better, start with a garden hose and a soft brush.
Will muriatic acid damage my brick? It can. Used wrong, it etches brick, dissolves lime mortar, and leaves salts that bloom into new efflorescence. If acid is truly needed, the wall must be soaked first, the acid diluted, dwell time short, and everything rinsed thoroughly.
How do I remove efflorescence? Usually a dry brush or plain water removes the powder. Skip the acid — efflorescence keeps returning until you fix the moisture getting into the masonry. On commercial elevations the same restraint applies at a much bigger scale, which is why an industrial cleaning contractor in Atlanta works to a written spec instead of turning the pressure up.