Does Pressure Washing Remove Moss?

There’s something deeply satisfying about pressure washing a mossy patio. Watching that jet of water blast away years of green growth, revealing clean stone underneath. It’s instant gratification.

But here’s what nobody tells you: pressure washing alone isn’t really solving your moss problem. It’s just resetting the clock.

Yes, Pressure Washing Removes Moss

Let’s be clear: a pressure washer will absolutely remove moss from most hard surfaces. The high-pressure water jet physically blasts it off. No chemicals needed, no waiting around, just immediate visible results.

For sheer speed and satisfaction, nothing beats it. A mossy patio that would take hours to scrub by hand can be cleaned in under an hour with a decent pressure washer.

So what’s the problem?

The Regrowth Issue

Pressure washing removes moss. It doesn’t kill moss. And that distinction matters more than you might think.

When you blast moss off with water, you’re removing the visible growth but leaving behind microscopic spores and fragments embedded in the surface. These survivors start regrowing almost immediately. In the right conditions, your patio can be visibly green again within weeks.

Moss spreads through spores that are everywhere in the air. A freshly pressure-washed surface is actually quite inviting to new moss. You’ve roughened the texture, opened up pores, and created plenty of places for spores to settle.

This is why moss keeps coming back despite your annual pressure washing ritual. You’re cleaning the surface but doing nothing to make it hostile to moss.

The Damage Problem

Beyond regrowth, pressure washing comes with real risks of damage.

Soft stones like sandstone and limestone are particularly vulnerable. The high-pressure water erodes the surface, wearing away detail and creating a rougher texture that actually holds more water and grows more moss.

Pointing between slabs gets blasted out. You’ll see gaps opening up in the joints, which then need repointing. These gaps also create perfect sheltered spots for moss to establish.

Brick can be damaged too, especially older or softer varieties. The surface gets eroded, edges become rounded, and the brick becomes more porous.

Even tough materials like concrete can suffer if you use too much pressure or hold the nozzle too close. Etching and pitting create a surface that’s harder to keep clean.

Wooden decking is particularly at risk. Pressure washing can splinter the surface, raise the grain, and force water deep into the timber where it causes rot.

The Right Way to Use a Pressure Washer

None of this means you should never pressure wash. Used correctly, it’s a useful tool. The key is combining it with proper treatment.

Here’s the approach that actually works:

Treat first. Apply a moss killer to the affected areas and wait for it to work. This typically takes one to two weeks. The moss will change colour as it dies.

Then pressure wash. Once the moss is dead, it releases its grip on the surface and comes off much more easily. You can use lower pressure and still get excellent results, reducing the risk of damage.

The treatment also leaves an active residue that continues working after you’ve cleaned. This hostile environment slows regrowth significantly, giving you months rather than weeks before the green returns.

Pressure Washer Settings That Minimise Damage

If you’re going to pressure wash, these practices reduce the risk of damage:

Use the lowest effective pressure. Start low and increase only if needed. Most moss removal doesn’t require maximum power.

Keep your distance. Hold the nozzle at least 30cm from the surface. Closer means more concentrated force and more potential damage.

Use a fan nozzle, not a pinpoint jet. The wider spray pattern distributes pressure more evenly and reduces the risk of etching.

Keep the nozzle moving. Never hold it in one spot. Constant movement prevents concentrated damage.

Work at an angle. Spraying at 45 degrees is gentler than hitting the surface head-on.

Test first. Try your settings on an inconspicuous area before doing the whole patio.

Surfaces to Avoid Pressure Washing

Some surfaces really shouldn’t be pressure washed at all, or only with extreme care:

Soft sandstone and limestone. These erode easily and the damage is permanent. A stiff brush after treatment is safer.

Old brick with lime mortar. The mortar is softer than modern cement and blasts out easily.

Painted or sealed surfaces. High pressure can strip coatings and finishes.

Wooden structures. Fencing, decking, and garden furniture all risk splintering and water damage.

Render and exterior walls. High pressure can crack render and force water behind it.

For these surfaces, the treat-and-brush method is both safer and more effective. If you don’t own a pressure washer or prefer to avoid the risks altogether, our guide to cleaning a patio without a pressure washer walks through every alternative method step by step.

When Pressure Washing Makes Sense

Pressure washing does have its place in moss control:

For initial clearing of heavy growth on tough surfaces like concrete or hard granite, it’s fast and effective.

After treatment, when moss is dead and loose, gentle pressure washing can speed up removal.

For quick results before an event, when you need the patio clean today and can deal with long-term prevention later.

As part of annual maintenance, combined with preventative treatment to slow regrowth.

The mistake is relying on pressure washing alone and expecting lasting results.

The Better Long-Term Approach

If you want to spend less time fighting moss, focus on treatment and prevention rather than repeated pressure washing.

Treat moss properly with a product that kills it and leaves residual protection. The moss comes off more easily and stays away longer. If you’re unsure which moss killers pair best with pressure washing, it’s worth comparing chemical treatments before committing to a method.

Address the underlying causes. Improving drainage, reducing shade, and keeping surfaces clean all help.

Apply preventative treatment. A light application in spring and autumn stops moss establishing before it becomes visible.

Reserve pressure washing for occasional deep cleans rather than your primary moss control method.

Our everything you need to know about killing moss guide covers the complete approach to long-term moss control.

Frequently Asked Questions

Can pressure washing damage my patio?

Yes. High-pressure settings can erode pointing between slabs, pit softer stones like sandstone, and damage the surface of concrete over time. Use the lowest effective pressure setting, hold the lance at a 45-degree angle, and avoid directing the jet into joints. Natural stone and older surfaces are most vulnerable.

How soon after moss killer can I pressure wash?

Wait at least 7-14 days until the moss is completely dead, brown, and crumbly. Pressure washing too early scatters live fragments across your surface, creating new colonies. Test a small area first. If the moss brushes off cleanly, it is ready for pressure washing.

Is a pressure washer better than a stiff brush for removing dead moss?

For large areas, a pressure washer is faster. For small areas or delicate surfaces like Indian sandstone, a stiff brush is safer and equally effective on truly dead moss. Either method works well once the moss has been properly killed by chemical treatment first.

Why does moss come back worse after pressure washing?

Pressure washing roughens smooth surfaces and opens up pores and cracks, creating more anchor points for new moss spores. It also scatters live moss fragments into joints where they regenerate. Treating with moss killer before and after pressure washing breaks this cycle.

Do I need a pressure washer to remove moss?

No. A stiff broom or brush works well for removing dead moss after chemical treatment. Many people achieve excellent results without ever using a pressure washer. Our guide to cleaning a patio without a pressure washer covers all the alternatives, from soapy water to spray-and-leave treatments. The spray-and-leave approach is simpler, cheaper, and less likely to damage surfaces.

What PSI setting should I use for moss removal?

For most patios, 1,500-2,000 PSI is sufficient for removing dead moss without damaging surfaces. Never exceed 2,500 PSI on standard paving. Use a fan nozzle rather than a pinpoint jet, and keep the lance moving to avoid concentrating pressure on one spot.