How To Clean Patio Slabs

A patio takes a beating. Rain, algae, moss, spilled barbecue grease, leaf tannins and general foot traffic all conspire to turn a smart outdoor space into something tired and slippery. Learning how to clean patio slabs properly, without wrecking the surface or the joints, is one of the most cost effective bits of home maintenance you can do. Get it right and you can add years to the life of your paving. Get it wrong, and you can etch the stone, blow out the pointing or drive water into the substrate.

I have cleaned and restored more patios than I can count, from Yorkstone terraces to modern porcelain and budget concrete flags. This article sets out exactly how to do the job safely, what kit to use, what to avoid, and what it costs if you decide to bring in a professional instead.

Why Patio Slabs Get Dirty in the First Place

Understanding the enemy helps you choose the right treatment. Most of what you are cleaning falls into a few categories.

Organic growth. Green algae, dark green to black moss, and lichen thrive in the damp UK climate, especially on north facing patios and anywhere shaded by fences or trees. This is the most common cause of that slippery film underfoot.

Ingrained dirt and grime. Airborne pollution, soil splashback and general use leave a grey film that dulls the surface over time.

Organic staining. Fallen leaves, particularly from oak and sycamore, leach tannins that leave brown marks. Bird droppings and berries do similar damage.

Man made stains. Barbecue grease, cooking oil, rust from metal furniture feet, and paint spills all need targeted treatment rather than a general wash.

The point here is simple. There is no single magic cleaner. What works on green algae will do nothing for a rust stain, and what shifts grease might damage a porous natural stone.

Identify Your Patio Material Before You Start

This step matters more than any other. The material dictates the cleaning method, the pressure you can safely use and the chemicals you can apply.

Material	Porosity	Pressure washing	Acid based cleaners
Porcelain	Very low	Safe at moderate pressure	Generally safe, but check
Concrete slabs	Medium	Safe, keep nozzle moving	Avoid, can etch surface
Indian sandstone	High	Low pressure only	Never use acid
Limestone	High	Low pressure only	Never, acid dissolves it
Yorkstone	Medium to high	Low to moderate	Avoid
Slate	Low to medium	Moderate, avoid flaking edges	Avoid

If you are unsure what you have, test any product on a hidden corner first and wait 24 hours to check for discolouration. Limestone and acid are a disaster waiting to happen. The acid reacts with the calcium carbonate and eats into the surface, leaving a permanent dull patch.

The Tools and Products You Will Need

You do not need a van full of kit. For most patios, this list covers it.

• A stiff bristled broom or deck brush. Avoid wire brushes on soft stone.
• A garden hose with a decent flow, or a bucket and watering can.
• A pressure washer, ideally with a fan or rotary flat surface attachment.
• A dedicated patio cleaner suited to your material.
• Sodium hypochlorite or a proprietary algae and moss killer for organic growth.
• A plastic scraper for stubborn deposits.
• Rubber gloves, eye protection and old clothing.
• Plastic sheeting to protect nearby plants and borders.

A patio cleaner attachment for your pressure washer is worth the money. It encloses the spray, spins two nozzles under a hood and gives a far more even finish than waving a lance around. It also stops you soaking yourself and the neighbour's washing.

How To Clean Patio Slabs Step by Step

Here is the method I use on a typical domestic patio. Set aside half a day for an average sized area, more if it is heavily soiled or large.

1. Clear and sweep

Move furniture, pots and the barbecue off the patio. Sweep the whole area thoroughly with a stiff broom to remove loose debris, leaves and grit. This alone lifts a surprising amount of surface dirt and stops you grinding it in later.

2. Pull weeds and check the joints

Remove any weeds growing between slabs by hand or with a weeding knife. If your pointing is cracked, loose or missing, sort that before or after cleaning rather than blasting it out with a pressure washer. Our guide on How to Repoint Patio Slabs and Stop Weeds Coming Back walks through the repointing process in detail.

3. Protect surrounding areas

Cover nearby borders and prized plants with plastic sheeting, especially if you are using chemical treatments. Sodium hypochlorite will scorch foliage and lawns. Give beds a good watering first so any splash is diluted.

4. Apply your cleaning solution

For general grime, a proprietary patio cleaner diluted per the label works well. For heavy algae and moss, apply a hypochlorite based cleaner or a dedicated moss killer. Work it in with a stiff broom and leave it to dwell for the time stated, usually 10 to 20 minutes. Do not let it dry out on the surface.

5. Agitate the stubborn areas

Scrub heavily soiled patches by hand. The chemistry does most of the work, but agitation breaks the surface film and lets the cleaner penetrate.

6. Rinse or pressure wash

Rinse thoroughly with clean water. If you are pressure washing, keep the nozzle at a consistent distance, usually 20 to 30cm from the surface, and move steadily. Never hold the lance in one spot on soft stone, as you can scour a channel into it within seconds. Work in overlapping passes so you do not leave tiger stripes.

7. Let it dry and reassess

Allow the patio to dry fully, ideally 24 hours in dry weather. Only then can you see the true result. Any remaining stains can be spot treated at this stage.

8. Refill joints and consider sealing

Pressure washing often removes jointing sand or loosens pointing. Top up kiln dried sand in block paving joints or repoint mortar joints as needed. On porous natural stone, a breathable sealer applied to a dry patio helps repel stains and slows algae return.

Dealing With Specific Stains

General cleaning will not shift everything. Here is how to tackle the awkward ones.

Black spot lichen. Those tiny black circular marks on sandstone are lichen, and they are notoriously stubborn. A general wash will not budge them. You need a dedicated black spot remover, and even then it may take two applications a few weeks apart. Never attack them with a pressure washer alone, as you will pit the stone before you shift the lichen.

Grease and oil. Sprinkle the area with baking soda or a proprietary degreaser to draw out the oil, leave it, then scrub with hot water and washing up liquid. Cat litter works well on fresh spills to absorb the bulk first.

Rust. Rust from furniture feet or metal ornaments needs an oxalic acid based rust remover. Standard patio cleaner will not touch it. Follow the product instructions and rinse well.

Efflorescence. That white powdery bloom on newer concrete and some natural stone is mineral salts working their way out. Brush it off dry first. A specialist efflorescence remover handles the rest, but often it fades naturally over the first year.

Pressure Washing: Use With Care

A pressure washer is the fastest route to a clean patio, but it causes more damage than any other tool when misused. I have been called to fix patios where an enthusiastic owner has stripped the mortar out of every joint and scoured swirl marks into soft sandstone.

Keep these rules in mind.

• Use the widest fan setting or a flat surface cleaner, never the pinpoint jet on paving.
• Keep the lance moving at all times.
• Stay at least 20cm from the surface on natural stone.
• Angle the spray so you are not blasting directly into the joints.
• Expect to top up jointing afterwards. It almost always needs it.

The Health and Safety Executive offers useful guidance on the safe use of pressure washers, including protective equipment and the risk of high pressure injection injuries. Read it at the HSE guidance on water jetting before you start if you are new to the kit.

Cost Breakdown: DIY vs Professional Cleaning

Cleaning your own patio is one of the cheaper jobs to take on yourself. Here is a realistic view of both routes based on 2026 UK prices.

Item	DIY cost	Notes
Patio cleaner (5L)	£12 to £25	Covers roughly 30 to 50 square metres
Moss and algae killer	£10 to £20	Concentrate goes further
Pressure washer hire (day)	£30 to £50	Or buy a domestic unit for £80 to £200
Surface cleaner attachment	£25 to £60	One off purchase
Sealer (if used)	£30 to £70	Natural stone only

For a professional clean, expect to pay around £3 to £6 per square metre for a straightforward pressure wash and treatment. Many firms have a minimum charge of £120 to £200 to cover call out and setup. A typical 25 square metre patio might cost £150 to £300 cleaned and treated, more if resanding or sealing is included.

If your patio is beyond saving, cleaning is money down the drain. In that case it is worth reading How Much Does It Cost to Install a New Patio in the UK in 2026? Porcelain vs Sandstone vs Concrete Slab Prices, Ground Prep and Labour Rates Explained to weigh cleaning against replacement.

Common Mistakes To Avoid

Most patio cleaning disasters come down to a handful of avoidable errors. I see the same ones again and again.

Using acid on limestone or sandstone. Acidic cleaners, including some brick cleaners and patio products, will etch and dull calcium rich stone permanently. Always check the product is suitable for your material.

Holding the pressure washer too close. On soft stone, you can cut visible lines into the surface in seconds. Once it is scoured, there is no fixing it short of replacing the slab.

Blasting out the pointing. If your mortar joints are weak, a pressure washer will destroy them. You then have open joints where weeds and water get in, and a repointing job on top of the cleaning.

Letting chemicals dry on the surface. Cleaners that dry out can leave streaks or bleach marks, especially hypochlorite. Keep the surface wet and rinse thoroughly.

Cleaning in the wrong weather. Applying treatments in full sun or before heavy rain wastes product. A dry, overcast day with no rain forecast for a few hours is ideal.

Ignoring runoff. Chemical laden water running into drains, ponds or watercourses can breach environmental rules. Direct runoff to soil or foul drains where permitted, and dilute well. The government guidance on preventing water pollution from cleaning activities explains your responsibilities.

Skipping the resanding step. After cleaning block paving especially, the joints need refilling with kiln dried sand to lock the blocks and keep weeds out.

How Often Should You Clean Your Patio?

For most UK homes, a proper clean once a year keeps a patio in good order. Late spring or early autumn works well. A quick brush and hose down every few weeks through the growing season stops algae building into a slippery layer.

North facing and shaded patios need more attention, as they stay damp and grow moss faster. A biannual treatment with a moss inhibitor keeps regrowth in check.

Sealing natural stone every few years, depending on the product, reduces how much dirt penetrates and makes each subsequent clean easier and quicker.

Keeping Your Patio Cleaner For Longer

A few habits stretch the time between deep cleans.

• Sweep regularly to stop leaves rotting and staining the surface.
• Move furniture occasionally so algae does not build under fixed points.
• Clear leaf fall promptly in autumn, particularly under trees.
• Keep gutters and downpipes clear so water does not sheet across the patio.
• Apply a preventative moss treatment in early spring.
• Reseal porous stone on schedule.

If you are planning a new outdoor space and want low maintenance from the start, porcelain is the easiest surface to keep clean. For inspiration on making the most of a compact area, our piece on Small Patio Ideas is worth a look.

What About Block Paving and Driveways?

Block paving is cleaned along similar lines, but the jointing sand and the interlocking nature of the blocks mean the process differs in the detail, particularly around resanding and stabilising the surface afterwards. If your project includes a driveway or paved paths, the dedicated guide on How To Clean Block Paving covers the specifics.

Frequently Asked Questions

Can I clean patio slabs with just washing up liquid and water?

For light grime, yes. A bucket of hot water with a squirt of washing up liquid and a stiff brush will shift general surface dirt and mild greasiness. It will not touch established algae, black spot lichen or ingrained staining, though. For those, you need a dedicated patio cleaner or a hypochlorite based treatment. Washing up liquid is a fine maintenance option between deeper cleans, but it is not a substitute for the real thing on a neglected patio.

Will bleach damage my patio slabs?

Diluted household bleach is essentially sodium hypochlorite, which is the active ingredient in many patio cleaners, so it can be effective against algae and moss. The risks are that it can lighten coloured slabs, scorch nearby plants and lawns, and harm aquatic life if it reaches watercourses. Use it diluted, keep it off borders, rinse thoroughly and never use it near ponds. On natural stone with a coloured finish, test a hidden area first, as some products cause patchy fading. A purpose made patio cleaner is usually a safer and more predictable choice.

Do I need planning permission to clean or replace my patio?

Cleaning a patio needs no permission at all. Replacing an existing patio of the same size is normally permitted development and does not require planning consent. The main thing to watch is surface water drainage. If you are laying a new patio or expanding one so that surface water cannot drain naturally, you may need to use permeable materials or direct runoff to a soakaway. The rules on drainage and paving over front gardens are set out in the Planning Portal guidance on planning permission. For a straightforward clean, none of this applies.

How long does it take to clean an average patio?

For a typical 20 to 30 square metre domestic patio, allow half a day if you are pressure washing and treating it yourself. Add extra time if the surface is heavily soiled, if you are treating black spot lichen, or if you plan to resand joints and seal afterwards. Chemical treatments need dwell time, and the patio should dry fully before sealing, so a proper job with sealing often spans two days to allow for drying between stages.

Should I seal my patio after cleaning?

It depends on the material. Porous natural stone such as sandstone, limestone and Yorkstone benefits from a breathable sealer, which repels stains and slows algae return. Porcelain does not need sealing, as it is virtually non porous. Concrete slabs can be sealed but do not always require it. If you do seal, the patio must be completely dry and free of any cleaning residue first, or you will trap moisture and cause a cloudy finish. Always use a sealer rated for your specific material.

Final Thoughts

Cleaning patio slabs is well within reach for most homeowners, provided you match the method to the material and resist the temptation to blast everything at full pressure. Sweep first, treat the organic growth, work methodically, protect your borders and refill the joints afterwards. Do that once a year and your patio will stay safe underfoot and looking smart for decades.

If the job is large, the stone is delicate, or you would simply rather hand it to someone with the right kit and experience, a professional clean is affordable and quick. To compare options, post a job on BookaBuilderUK and get free quotes from vetted local tradespeople near you.