TL;DR
Brick is usually hard enough to survive pressure washing, but the mortar between the bricks often is not, especially on homes built before the mid-twentieth century when softer lime-based mortar was standard. Test a hidden joint first, keep pressure at roughly 1,000 to 1,800 PSI with a wide tip, and let a masonry-safe detergent do the work.
The brick is not the problem
Fired clay brick is dense and hard. A well-made brick face will take more force than most of a house exterior.
Mortar is a different material entirely. It is softer by design -- deliberately weaker than the brick so that movement in the wall cracks the joint rather than the brick, since a joint can be repointed and a cracked brick cannot.
That intentional softness is what fails under a pressure stream. A narrow tip held on a joint hollows it out in seconds, and once mortar is gone the wall has an open path for water directly into the structure.
Repointing is skilled work priced by the square foot, and it costs many times what the cleaning did.
Older mortar is much softer than modern mortar
The dividing line matters. Homes built before roughly the 1930s were commonly laid with lime-based mortar, which is much softer and more permeable than the modern cement-based mortars used since.
Lime mortar erodes under a garden hose held close, let alone a pressure washer. It also has to stay permeable, because it is part of how those old walls manage moisture.
Source: masonry conservation and repointing practice guidance
If your house is old, or you can see sandy, crumbly joints, the honest starting position is that this is a soft wash job and possibly a job for a mason rather than a cleaner.
Test before anything else
Pick a hidden area -- behind a downspout, a low corner, a wall behind shrubs.
The finger test. Run a fingertip along a mortar joint. If sand comes off on your skin, the mortar is already deteriorating and pressure will accelerate it dramatically.
The scratch test. Drag a key or a screwdriver tip lightly along a joint. Mortar that gouges easily will not survive washing.
The spray test. With the machine set low and a wide tip, spray a small hidden area from a distance for a few seconds, then look at the joint and at the runoff. Sand in the runoff means stop.
If any of these fails, switch to a garden hose, detergent, and a soft brush, and get the joints looked at.
The method
1. Prep. Close windows and doors, cut power at the breaker to exterior fixtures, cover what you cannot disconnect, and move furniture clear.
2. Soak the plants. Wet beds and shrubs with plain water, keep them wet, and rinse again at the end.
3. Pre-wet the wall, top down. Brick is absorbent. A dry wall pulls cleaner deep into the pores where it is hard to rinse out, which causes streaking and residue. Pre-wetting fills the pores with plain water first.
4. Apply a masonry-safe cleaner, bottom up. Work in sections small enough to return to before they dry. Applying bottom up keeps runs from streaking dry brick.
5. Dwell. Five to ten minutes, out of direct sun, never to dryness. Chemistry and time do the work here, exactly as in soft washing and when it applies.
6. Brush. A soft or medium-bristle masonry brush for stubborn areas. Never a wire brush -- it leaves metal particles that rust and stain the brick permanently.
7. Rinse, top down, wide tip, well back. If a machine is used, keep it in the 1,000 to 1,800 PSI range with a 25 or 40 degree tip, held a foot or more away, and never pointed straight into a joint. Material tolerances are in what PSI each surface can take.
8. Rinse thoroughly. Cleaner left in porous brick will bloom back to the surface as it dries.
Cleaner choices and one serious warning
Mild exterior detergents handle dust and film. Bleach-based exterior washes handle algae and mildew on shaded walls.
Acidic masonry cleaners exist for mortar smears and efflorescence and they work, but they are aggressive. They can burn the brick face, discolor it, and attack the mortar you are trying to protect. Dilute exactly as directed, always pre-wet, test in a hidden spot, and rinse very thoroughly.
Never combine an acidic masonry cleaner with a bleach-based product. Acid plus bleach releases chlorine gas. If you use both on the same job, finish one completely, rinse the wall until the runoff is clear, and only then start the other. Better still, choose one and stick with it.
Never use a wire brush, and never use a rotary or turbo nozzle on brick.
Problems that are not really cleaning problems
Efflorescence is a white powdery bloom of mineral salts pushed to the surface by moisture moving through the wall. Dry brushing removes it. If it returns, the cause is water in the wall, and repeated washing just adds more water.
Green and black growth concentrated at the bottom of a wall or under a downspout usually means splashback or a drainage problem. Cleaning helps for a season; fixing the water fixes it.
Spalling, where brick faces flake off, means water got into the brick and froze. That brick is failing and should not be washed at pressure at all.
Paint on brick is a separate decision. Pressure will take loose paint off along with mortar, and stripping painted brick is a specialist job.
If your masonry is patio or walkway rather than wall, the joint sand and moss questions differ -- see how to clean a brick patio.
Safety
Never work a wand from a ladder. The recoil is a genuine fall hazard, and brick walls are usually the tallest surfaces on a house. Wear eye protection and gloves, especially with any acidic product, and keep runoff out of storm drains where local rules require it.
If your home mixes brick with stucco, remember the stucco portions have far lower tolerance -- see cleaning stucco without stripping it.
FAQ
Can you pressure wash a brick house?
Usually yes, at low pressure with a wide tip held well back, but the mortar joints set the limit rather than the brick. Test a hidden joint first, keep pressure around 1,000 to 1,800 PSI, and never aim a stream directly into a joint. Older lime mortar may not tolerate a machine at all.
How do I know if my mortar is too soft to pressure wash?
Run a fingertip along a joint in a hidden area. Sand coming off on your skin means the mortar is deteriorating. A key dragged lightly along the joint that gouges it confirms it. If either test fails, use a garden hose, detergent, and a soft brush instead.
What PSI is safe for brick?
Roughly 1,000 to 1,800 PSI with a 25 or 40 degree tip held a foot or more from the wall, on sound modern mortar. Older homes with soft lime-based mortar should be washed with a garden hose and detergent instead. Test a hidden area before committing to any setting.
What is the best cleaner for exterior brick?
A mild exterior detergent for ordinary soil and a diluted bleach-based wash for algae and mildew. Acidic masonry cleaners work on mortar smears and efflorescence but are aggressive, so pre-wet, dilute exactly, and test first. Never use an acid and a bleach product together.
Why does white powder keep appearing on my brick?
That is efflorescence, mineral salts carried to the surface as moisture moves through the wall and evaporates. Dry brushing removes what is there. If it keeps returning, water is entering the masonry, and the fix is drainage or repair rather than repeated washing.
Brick walls reward patience and punish shortcuts, and the joints decide the whole approach. Our pressure washing service tests the mortar before choosing a method. Get a quote and we will look at the masonry with you.