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The brick industry's own guidance caps pressure washing at 400 PSI measured at the nozzle tip — and a typical consumer pressure washer produces four to eight times that. That single fact reframes the whole job. Brick is not a surface you blast clean; it is a surface you clean chemically and rinse gently, and the pressure washer's role is to be the rinse, on its lowest setting, from a distance.
The Brick Industry Association's Technical Note 20, Cleaning Brickwork (2018) is explicit about it. It defines very low pressure as under 100 PSI, low pressure as 100 to 400 PSI, medium as 400 to 800 PSI — permitted only if the brick manufacturer allows it — and states of anything above that: "High-pressure water cleaning is not appropriate for brick and may damage the brickwork." It also specifies a stainless steel 25 to 50 degree fan tip held a minimum of 12 inches from the surface.
Why the limit is so low
Two reasons, and both produce damage that does not repair.
The mortar is meant to be the weak part. Mortar joints are formulated to be softer than the brick so a wall can accommodate movement without cracking the units themselves. That design decision means the joint face is the first thing a high-pressure jet erodes. Once the mortar is washed back, water gets into the wall, and the fix is repointing — a skilled, slow, expensive job that costs far more than any cleaning ever saved.
The brick has a skin. Fired clay brick has a denser outer surface formed in the kiln. Strip it and you expose the more porous body underneath, which holds dirt, gets dirty faster, absorbs more water and becomes more vulnerable to freeze-thaw spalling. Technical Note 20 makes the same point about abrasive methods, noting that removing the outer surface increases water penetration and makes future cleaning harder. Sand-finished, glazed, coated and slurry-finished brick should not be pressure washed at all.
For a historic building, be more careful still. The National Park Service's Preservation Brief 1 frames the whole subject around using the gentlest effective method, and treats inappropriate cleaning as a leading cause of damage to historic masonry. If the building is old, listed, or has soft lime mortar, get advice before touching it with a machine.
The numbers, side by side
| Category (BIA Technical Note 20) | Pressure at the nozzle | Use on brick? |
|---|---|---|
| Very low | Under 100 PSI | Yes — pre-wetting and saturating |
| Low | 100–400 PSI | Yes — rinsing after a cleaner |
| Medium | 400–800 PSI | Only if the brick manufacturer permits it |
| High | Above 800 PSI | Not appropriate for brick |
| Cleaning solution spray | 30–50 PSI maximum | Higher pressure drives the solution deep into the masonry |
| Typical consumer pressure washer | 1600–3200 PSI | Far above the limit — use the low-pressure tip and distance |
So how do you use a 2000 PSI machine on a 400 PSI job? Three levers: the tip, the distance, and throttling the trigger. Fit the black soap or low-pressure tip, which is what the injector uses and which delivers a fraction of the machine's rated output. Stand well back — pressure at the surface drops sharply with distance, which is why the 12-inch minimum in the standard is a minimum and not a target. And do not squeeze the trigger fully. If your machine has a variable wand, use its lowest setting. If you are cleaning a wall where the mortar is already soft or crumbling, put the machine away and use a garden hose and a brush.
Tools and materials
- A pressure washer used gently — an electric in the 1600–2000 PSI class is easier to control here than a gas machine. See current rankings.
- The black soap / low-pressure tip, and a 40° white tip as the narrowest you will fit. A fresh nozzle set costs a few dollars and worn tips spray unevenly.
- A long-handled stiff bristle brush. Non-metallic — a wire brush leaves iron particles that rust-stain the wall.
- A proprietary masonry cleaner, or a general-purpose pressure washer detergent such as Kärcher multi-purpose detergent (paid link) for ordinary dirt and organic growth. For heavier work, Oxy Solve house and siding cleaner (paid link) is an oxygenated option formulated to run through an injector.
- A garden hose, plastic sheeting for windows, doors and plantings, eye protection and gloves.
Do not use unbuffered muriatic (hydrochloric) or hydrofluoric acid. Technical Note 20 is unambiguous about this. Acid produces the discoloration known as acid burn, particularly on lighter brick, and can trigger vanadium and manganese staining that is dramatically harder to remove than whatever you started with.
The method
- Test an inconspicuous area first — a rear wall, a garage side, a section behind a shrub. Give it a week and look at it in dry conditions before doing the front of the house. Every masonry cleaning guide says this and almost nobody does it.
- Wait if the brickwork is new. At least seven days after completion, so the mortar has hardened. Cleaning earlier washes soft mortar out and drives dissolved mortar into the brick face.
- Pick the weather. Above 40°F, overcast, and ideally with no freeze expected for a week afterward. Cleaner drying on the wall in direct sun streaks and stops working.
- Protect everything. Cover windows, doors, trim and light fittings; many masonry cleaners attack glass and metal. Wet the plantings below thoroughly with clean water before and after.
- Saturate the wall — and the wall below it. This is the step most people skip and it matters more than any other. A dry brick absorbs the cleaning solution and the dissolved dirt, carrying the stain into the body of the unit where you cannot reach it. Wet the area and everything beneath, at very low pressure, and keep it wet through the whole process.
- Apply the cleaner at low pressure. Brush it on or use a pump sprayer with a wide fan at 30 to 50 PSI. The soap tip on a pressure washer is the equivalent. Work in small sections you can rinse before anything dries.
- Agitate with the brush. This is where the cleaning happens. A stiff non-metallic brush on a pole does what pressure cannot do safely.
- Rinse within five to ten minutes, before the solution dries, using low pressure and plenty of water. Rinse from the top down, and keep going after the wall looks clean — residual cleaner left in the masonry causes staining later.
- Work small sections, top to bottom, all the way along. Half-cleaned walls with a tide line are the second most common regret here. Finish to a natural boundary such as a corner or a downpipe.
Efflorescence: clean the symptom, find the cause
The white powdery bloom on brick is efflorescence — water-soluble salts brought to the surface as moisture moves through the wall and evaporates. Fresh efflorescence generally comes off with plain water and a stiff brush, and often weathers away on its own.
The part that matters is that it is a moisture indicator. If efflorescence keeps returning, water is getting into the masonry: a failed flashing, a blocked or leaking gutter, ground splash-back against the wall, a cracked joint, or rising damp. Cleaning it repeatedly without fixing the water source is a maintenance treadmill, and the underlying moisture is doing far more damage to the wall than the salt on the surface ever will.
The mistakes that cost repointing
The turbo nozzle. A rotary tip on brick blows mortar out of joints in seconds. It is the fastest way to a repointing bill.
Not pre-wetting. Dry brick absorbs cleaner and dissolved dirt, producing a stain deeper than the one you removed.
Letting cleaner dry on the wall. Streaks, and cleaner left in the masonry stains later.
Muriatic acid. Acid burn on light brick, and vanadium or manganese staining that a contractor will charge you to remove.
Metal brushes. Iron particles embed in the surface and rust-stain the wall in the first rain.
Spraying upward into weep holes. Brick veneer walls have weep holes at the base of each course line for drainage. Driving water into them puts it inside the cavity.
Safety
A pressure washer can break skin even at moderate settings. A high-pressure injection injury forces water, grit and bacteria into the tissue beneath through a puncture that can look trivial, and it is a surgical emergency rather than a wound to clean at home. A 2023 analysis in the journal Hand of a decade of US emergency-department records found that pressure washers accounted for roughly 90% of high-pressure injection hand injuries. Never point the wand at anyone, never brace a hand in front of the tip, and bleed the pressure before changing a nozzle. More: pressure washer injection injuries.
Masonry cleaners deserve respect of their own — eye protection, gloves, long sleeves, and never mixing products. And do not work off a ladder with a pressure washer; the recoil is enough to unbalance you. Use an extension wand from the ground, or hire someone.
Where to go next
If the surface you are actually facing is a brick or paver patio rather than a wall, the rules are looser on the pavers themselves but the jointing sand still washes out — see how to pressure wash a patio. For house walls generally, how to pressure wash a house and what soft washing is cover the low-pressure approach that suits masonry and siding alike. For the detergent, the best pressure washer soaps.
We never buy or physically test the products we recommend — guidance here comes from published industry standards, manufacturer instructions and aggregated owner reports. Method: how we rank. Hub: leaf blowers & yard cleanup.