How to Clean Exterior Brick

Brick reads as the toughest thing on the house, and in some respects it is. But cleaning brick isn't really a question about the brick at all — it's a question about the mortar between it. The joints are usually softer than the brick face by design, and they are what holds the whole wall together. On masonry, force reaches the mortar long before it troubles the brick, and once the joints start to go, you've quietly converted a cleaning afternoon into a repair project. So the first thing to establish is not how to clean the wall but what state it's in, because sound brick and tired old brick call for genuinely different treatment.

The joints, not the faces, set the limit

It's worth being precise about why mortar is the thing to protect. In a masonry wall, mortar is meant to be the sacrificial element — softer than the brick so the joints, not the units, absorb movement and stress. That intended softness is also its vulnerability: a high-pressure stream erodes the joints, opens gaps, and lets water travel behind the brick and into the wall. The water is the real cost. It doesn't just look bad; it can feed moisture problems inside the wall, and repointing eroded joints is an actual repair, not a rinse. Seen through how pressure washing works, the danger is plain — the tool is built to erode and dislodge, and soft mortar is exactly what it erodes fastest.

Two walls, two approaches

The dividing line is condition, and it changes everything downstream.

Sound, modern brick in good repair, with firm joints, can often take a fair amount — including careful pressure washing. The face is hard and the mortar is intact enough to resist erosion. Aged or soft brick paired with old mortar is a different animal. Older mortar tends to be softer to begin with, and years of weathering can leave both the brick and the joints fragile, so force a sound wall would ignore can wash crumbling mortar out and even flake the face of soft brick. Here gentle methods aren't a preference — they're the only safe option.

The catch is that condition isn't always readable from the yard. If the mortar looks powdery, cracked or recessed, or crumbles when you press a finger to it, treat the wall as fragile no matter how solid the brick looks from a distance.

A low-pressure routine that spares the mortar

For most home brick — and for anything you're the least bit unsure about — the safe default is low-pressure and cleaner-led:

1. Rinse the wall gently to carry off loose dirt.
2. Apply a masonry cleaner per its directions, and let it dwell to break down grime and growth.
3. Scrub problem areas with a soft or medium brush instead of escalating the pressure.
4. Rinse at low pressure, keeping the stream from digging into the joints.

Because brick is porous and the mortar is vulnerable, this is a natural soft washing surface in most cases. Letting the chemistry carry the work protects the joints in a way that raw force never can.

Reading efflorescence and growth as moisture

Two problems turn up on brick constantly, and both are really moisture stories wearing a cleaning disguise.

Efflorescence is the white, powdery bloom that appears when moisture moves through the masonry, carries dissolved salts to the surface, and evaporates, leaving the salt behind. Gentle methods and an appropriate cleaner can take the deposit off, but the deposit is only the symptom. As long as moisture keeps traveling through the wall, the efflorescence keeps coming back — so the durable fix is usually reducing the water reaching the brick, not scrubbing harder.

Green and black organic growth — algae, mildew and their staining — is alive, which means it needs a cleaner rather than force. A cleaner treats the growth at its source; blasting strips the visible layer, threatens the mortar, and lets the growth return anyway. The same low-pressure approach used for algae on exterior walls transfers directly to brick, and where growth or efflorescence keeps returning, green growth that returns on siding walks through the moisture-and-shade logic that drives it on masonry too. Watch, as you clean and after, for mortar washing out or looking recessed, chips or spalling on the brick face, joints that widen enough to see into, damp or stained interior walls, or growth that comes back fast — each one is the wall reporting a problem a clean won't cure.

Old masonry wants a lighter hand

Historic and aged masonry deserves its own category. It often pairs soft, handmade brick with lime-based mortar, and both can be permanently harmed by modern high-pressure methods and harsh chemicals. On material that can't be replaced, an aggressive clean isn't merely risky — it can do damage nothing undoes. The governing instinct here is restraint: gentle methods, tested carefully in an inconspicuous spot, and a strong bias toward handing the work to specialists who understand how historic masonry is meant to be cleaned. That same bias toward help applies whenever the mortar is crumbling and may need assessment or repointing, whenever the wall is large or high enough to add real height risk, or whenever you simply can't tell how sound the brick and joints are — a professional can judge what a wall will safely take before the first drop of water hits it. When the material is irreplaceable, the cost of getting it wrong dwarfs the cost of doing less.