Cleaning Brick and Masonry Safely

Brick reads as one of the toughest surfaces on a house, which is why so many people aim a pressure washer at it and regret it later. The brick face may shrug off the spray, but the mortar between the bricks is softer by design, and weathered mortar is softer still. High pressure scours those joints out and drives water into the wall. The safe way to clean masonry is almost the opposite of what instinct suggests: low pressure, a cleaner suited to the job, and enough patience to let the solution work. Done that way, ordinary dirt, efflorescence and organic growth come off without touching the mortar.

Why mortar is the vulnerable part

A masonry wall is a system of two materials with very different jobs. The brick or stone units carry the load and face the weather. The mortar joints bind them, and crucially, mortar is meant to be softer and more sacrificial than the units it holds. That is not a flaw; it lets the joints absorb movement and, when the time comes, be replaced without disturbing the brick.

The trouble for cleaning is that soft, weathered mortar has very little resistance to a concentrated stream of water. A pressure washer that leaves the brick face untouched can carve visible grooves into aged joints, wash out the outer layer of mortar, and open gaps that let water straight into the wall. Once water is inside masonry it has plenty of ways to cause harm: it feeds efflorescence, it fuels freeze-thaw damage in cold climates, and it can reach framing behind the wall.

So the risk in cleaning brick is rarely the brick. It is eroding the mortar and pushing water where it does not belong. Every choice below flows from protecting the joints.

The low-pressure method

The reliable approach borrows from soft washing: let a cleaning solution do the chemical work, use gentle mechanical help, and keep water pressure low throughout.

What you need

• A cleaner formulated for masonry, mixed per its label
• A soft or natural-bristle brush; avoid wire brushes, which shed and stain
• A garden hose, or a pressure washer used only on a low-pressure setting with a wide tip
• Plastic sheeting and water for protecting plants and windows
• Gloves and eye protection

The steps

Start by protecting the surroundings. Pre-wet plants near the wall and cover the ones you cannot move, and rinse them again afterward, because cleaner runoff can scorch landscaping. Our guide to protecting plants during exterior cleaning covers this in detail.

Rinse the wall gently with plain water first to clear loose dust. Then apply the masonry cleaner from the bottom up to avoid streaking, keep it wet, and give it the dwell time on the label so it can loosen dirt and kill growth. Work a section with the soft brush, following the joints and the brick face without scrubbing hard. Rinse from the top down at low pressure and check the result before moving on.

If you use a pressure washer at all, use it only as a rinse on a low setting with a wide-angle tip, held well back from the wall, and never point a narrow tip at the joints. The choice of tip matters enough that our nozzle guide is worth reading before you start.

Efflorescence and organic growth

Two specific problems come up on masonry often enough to treat on their own.

Efflorescence

The chalky white bloom on brick and foundation walls is efflorescence: mineral salts left on the surface as water that carried them evaporates. It is a symptom of moisture moving through the masonry, not a stain sitting on top of it. Light efflorescence often brushes off dry with a stiff natural or nylon brush, and a masonry-safe cleaner handles heavier deposits. The catch is that it returns as long as water keeps moving through the wall, so lasting relief comes from managing that moisture. We cover the full picture in efflorescence on foundation walls.

Algae, mildew and moss

Shaded, damp walls, especially north-facing ones, grow green and black film and sometimes moss. The fix is chemical, not mechanical: a masonry-safe solution applied at low pressure, allowed to dwell, then gently rinsed, kills and lifts the growth without grinding the joints. Scrubbing hard or blasting it wastes effort and endangers the mortar. Improving airflow and cutting back nearby plants slows regrowth.

Matching the problem to the approach

Problem	Safe approach	What to avoid
General dirt and grime	Masonry cleaner, soft brush, low-pressure rinse	Narrow high-pressure tips on the joints
Efflorescence (white bloom)	Dry brushing first, then masonry-safe cleaner; address the moisture source	Sealing over damp brick, trapping water inside
Algae and mildew	Soft-wash solution, dwell time, gentle rinse	Scrubbing hard or blasting the growth off
Moss in the joints	Cleaning solution, careful hand removal	Digging it out with wire tools that gouge mortar
Loose or missing mortar	Repoint before cleaning	Washing a wall with open joints

Common mistakes

• Treating brick as indestructible. The face may be tough, but the mortar is soft and the wall is only as sound as its joints. Force is the enemy here.
• Pointing high pressure at the joints. A narrow tip carves out weathered mortar and drives water into the wall, causing damage you will not see until later.
• Cleaning a wall with failing mortar. Washing before repointing pushes more water inside. Fix the joints first.
• Reaching for strong acid as a default. Masonry acids can etch and discolor brick and burn skin when misused. For routine dirt and growth, a masonry cleaner is safer and usually enough.
• Sealing brick reflexively after cleaning. The wrong sealer traps moisture and worsens efflorescence and freeze damage. Sealing is a wall-by-wall decision, not an automatic step.
• Forgetting the landscaping. Cleaner runoff scorches plants. Pre-wet, cover and rinse, as covered in what not to pressure wash and our plant-protection guide.

The takeaway

Cleaning brick safely comes down to respecting the mortar. The brick face can take more than the joints between it, and the joints are what hold the wall together and keep water out. Skip the high-pressure blast, reach for a masonry cleaner and a soft brush, give the solution time, and keep any rinse gentle and well back from the joints. Handle efflorescence as the moisture signal it is rather than a stain to scrub away, and treat algae chemically instead of mechanically. Do that, protect the plants below, and your masonry comes clean with its mortar and its water resistance intact.