TL;DR
Most brick patios come clean with a stiff broom, a detergent left to dwell for 10 to 15 minutes, and a rinse at moderate pressure -- not a narrow nozzle at full throttle. Brick and the sand or mortar between it are softer than they look, and moss in the joints is a drainage problem before it is a cleaning problem.
Why a brick patio needs a gentler hand than it looks like it needs
Brick is fired clay, and clay is porous. The face you walk on has a slightly denser skin from firing, and once that skin erodes the brick drinks in water, holds soil, and grows things faster than it did before.
The joints are the weaker half. A mortared patio has a mortar line that is deliberately softer than the brick around it, so movement cracks the joint instead of the unit. A sand-set patio has nothing between the bricks but graded sand, and that sand is easy to blast out in seconds. Either way, the fastest way to ruin a brick patio is to point a high-pressure stream at the seams.
Speed is the trap. A narrow nozzle looks like it is working because the cleaned stripe appears instantly, but part of what you are watching leave is the surface of the brick.
Source: Masonry and hardscape maintenance guidance
What is the right way to clean a brick patio?
Sweep the surface, pull weeds and moss out of the joints by hand, apply an outdoor detergent and let it dwell 10 to 15 minutes without drying, agitate stubborn areas with a stiff bristle brush, then rinse with a garden hose or a wide fan tip held well back. Refill joint sand afterward if any washed out.
Step one: handle weeds and moss by hand first
Pull weeds before any water touches the patio. Wet weeds tear off at the crown and leave the root behind, which means they are back in a few weeks.
Moss scrapes out best when it is dry and brittle. A narrow joint tool, an old flathead screwdriver, or a stiff wire joint brush will lift a surprising amount in one pass. Get the bulk out mechanically so the cleaner only has to handle what is left, rather than asking a detergent to dissolve a thick mat.
Moss keeps coming back for a reason. It grows where the surface stays damp, which usually means shade, poor drainage, or a downspout dumping nearby. If one section is always green, the long-term fix is more light, better runoff, or both.
Step two: detergent and dwell time do the real work
This is the step most people skip, and it is the one that replaces pressure. A cleaner needs contact time to break the bond between soil and brick.
Wet the patio first so the brick does not instantly absorb the cleaner. Apply an outdoor detergent or a dedicated masonry cleaner and keep the surface wet for 10 to 15 minutes. If it starts drying, mist it again. A cleaner that dries on the brick has stopped working and can leave a streak of its own.
Two safety limits that are not optional. Never combine a chlorine bleach product with any acidic cleaner, descaler, or rust remover -- that combination releases chlorine gas. Never mix bleach with an ammonia-based cleaner either. Use one product at a time, rinse fully between products, and work in open air.
Bleach solutions do kill moss and algae, but the runoff will damage lawn and plantings at the patio edge. If you use one, pre-wet the surrounding plants with plain water, keep the mix weak, and rinse the beds afterward. An oxygen bleach product is gentler on landscaping and works well on organic staining, though it needs a longer dwell.
Step three: agitate, then rinse gently
Scrub whatever did not release with a stiff bristle brush on a pole. Bristle contact does the job pressure would otherwise do, without the erosion.
Rinse with a garden hose and a spray nozzle where you can. If you use a pressure washer, stay at low pressure with a wide fan tip, hold the wand 12 to 18 inches back, keep it moving, and never aim into a joint. The same logic governs cleaning brick without blowing out the mortar on a wall and keeping joint sand in place on a paver surface. If you are unsure what your surface tolerates, what PSI each surface can take is the short version.
Rinse in one direction, toward the drainage side, and overlap every pass. Stopping and starting mid-run is what creates the striped look people notice a week later.
Step four: resand or repoint, then let it dry
Sand-set patios almost always lose some joint sand, even with a careful rinse. Sweep fresh joint sand back in once the surface is dry to the touch, work it down with the broom, and settle it with a light mist rather than a stream.
Mortared patios need a look at the joints instead. Crumbling or hollow-sounding mortar means water is getting under the brick, and that is a repointing job rather than a cleaning job. Cleaning a patio with failing joints only moves water into the base faster.
Let the patio dry fully before sealing anything. Sealer over trapped moisture clouds and peels, and stripping a failed sealer is a much bigger job than the original clean. For how outdoor surfaces differ from one another, see the exterior surface cleaning overview.
FAQ
How do I get moss out of brick patio joints?
Scrape it out mechanically while it is dry, using a joint tool or a stiff wire brush, then treat what remains with an outdoor cleaner and a 10 to 15 minute dwell. Moss returns wherever the surface stays damp, so improving light or drainage matters more long term than any single treatment.
Can I pressure wash a brick patio?
Yes, but at low pressure with a wide fan tip held 12 to 18 inches back and kept moving. Narrow tips erode brick faces, cut mortar, and blast joint sand out in seconds. Detergent dwell time should be doing most of the work, with the washer only rinsing what the cleaner loosened.
Does bleach damage a brick patio?
Diluted chlorine bleach usually will not harm the brick itself, but the runoff damages lawn and plantings at the edges and it can lighten colored mortar. Pre-wet surrounding plants, keep the mix weak, and rinse afterward. Never combine it with an acid or an ammonia-based cleaner.
What is the white powder on my brick patio?
That is efflorescence -- mineral salts carried to the surface as water moves through the masonry and evaporates. It brushes off dry, though it returns until the moisture source is addressed. Acid-based efflorescence removers exist but can etch brick and should be tested in a hidden spot first.
Do I have to put sand back between the bricks?
If the patio is sand-set, yes. Joint sand is what locks the units together and keeps them from shifting underfoot. Sweep fresh joint sand in once the surface is dry, work it down with a broom, and settle it with a light mist rather than a hose stream.
Should I seal a brick patio after cleaning it?
Sealing is optional. It slows staining, but it has to go on a fully dry surface or it will cloud and peel, and it needs reapplication every few years. Stripping a failed sealer is harder than the original cleaning, so many homeowners skip it and simply clean annually.
Why does my patio look striped after cleaning?
Uneven overlap or an inconsistent wand distance leaves alternating clean and dirty bands. Keep the tip the same distance off the surface, overlap each pass by roughly half, and rinse in one continuous direction. A surface cleaner attachment eliminates the problem entirely on flat runs.
Patio size, joint type, and how long the growth has been established all change what the job actually takes, and a mortared patio with failing joints needs a different plan than a sand-set one. Get a quote and we will look at the surface with you, or read more about pressure washing services.