Block Paving Cleaning: The Proper Method and When to Replace

Cleaning block paving properly is a five-part job: kill the weeds and moss, wash the surface at medium pressure, treat the stains, let it dry out fully, then brush kiln-dried sand back into the joints. The re-sanding is the step almost everyone skips, and it's the one that decides whether the drive still looks good in spring.

This is for the homeowner looking at a drive that went green over winter, black along the tyre lines, with weeds sitting in every joint. The good news: most of what you're seeing is in the joints and on the surface, not in the blocks themselves. It cleans up. Here's how it should be done, what goes wrong with a hired pressure washer, and the honest point where cleaning stops being the answer.

Why block paving goes green, black and full of weeds

Kiln-dried sand is what holds block paving together. Brushed into the joints, it locks each block against its neighbours and spreads the load of a car across the whole surface.

Rain, tyres and cleaning all push that sand out over time. Once the joints sit low, wind-blown grit and dust settle into them, seeds land, and suddenly every joint is a little flower bed. Moss and algae then spread across the blocks themselves, worst in shade and where water sits after rain. The green film is algae. The black spotting that survives a wash is usually lichen, and it roots into the face of the block, which is why plain water never shifts it.

So a drive that looks ruined is usually a drive that's lost its sand. That's fixable.

How to clean block paving: the proper process

This is the order we work in on a driveway, and the order that gets results if you're doing it yourself. Each step has a reason, and shuffling them is where jobs go wrong.

1. Clear and sweep. Everything off the drive, then a proper going-over with a stiff broom. Loose grit under a jet turns into a scouring agent.
2. Kill the growth first. Weeds by hand or with a paving-safe weedkiller, moss and algae with a biocide left to dwell. Dead growth washes off. Live growth just gets chopped up and spread into the joints you've already lost sand from.
3. Rotary surface clean. A rotary flat-surface cleaner is the right tool for the main area, not an open lance. It keeps the pressure even, contains the spray, and doesn't chew stripes into the blocks. A lance comes out for edges and corners only, held at a shallow angle.
4. Spot-treat oil and black spot. Fresh oil gets absorbed first, then degreased. Old oil and black spot need a chemical treatment and patience, not more pressure. Pressure alone just lightens the top of the stain.
5. Rinse and leave it to dry. Everything rinsed down, including splashed walls and the pavement outside. Then the drive is left to dry right through, joints included.
6. Re-sand with kiln-dried sand. Dry sand poured on, brushed diagonally into every joint, topped up until the joints are full. Ordinary sand won't do, it's damp and it bridges over the joints instead of falling into them.
7. Compact. A plate compactor (or a good thump with a rubber mallet on a small area) settles the sand down, then a final top-up pass. This is what puts the structure back into the surface.
8. Sealing, if you want it. Optional, quoted separately, and it locks the sand in so the joints don't empty again. We've written the honest pros, cons and timing in is block paving sealing worth it, because it isn't right for every drive.

The same approach, scaled down, is how we'd do a block-paved patio. Our patio cleaning method covers the slab and stone side of that.

Cleaning block paving with a pressure washer: the mistakes we get called to fix

A hired machine on a block paving driveway causes the same three problems, over and over.

Blasting the joints out. A pencil jet or turbo nozzle pointed straight down fires the jointing sand out in seconds. Marshalls, who make a good share of the block paving on British drives, say in their own cleaning advice that "the pressure washer should be angled at 30° and sprayed diagonally on a medium pressure", warning that otherwise it can "mark the surface of some paving materials and break up the jointing material".

Etching. Too much pressure, or the lance held too close, scours the face of the block. On patterned or coloured blocks it strips the finish, and it doesn't come back.

Tiger stripes. Stopping mid-pass, or working in narrow overlapping bands, leaves light and dark stripes that only show once the drive dries. By then the machine's gone back to the hire shop.

If you're hiring, the fix is simple: wide fan, medium pressure, lance at roughly 30 degrees about a foot off the surface, keep moving, work diagonally across the blocks rather than along the joints. And budget for the sand afterwards, because you will lose some whatever you do.

Drying time: the boring bit that makes or breaks the re-sand

Kiln-dried sand only flows into a joint if the joint is dry. Brush it onto a damp drive and it sticks to the surface, bridges over the gaps, and washes away with the next rain.

In summer, a washed drive can be dry enough in a day. In a London autumn, give it 24 to 48 hours of dry weather before you sand it. The Met Office's Heathrow station data tells the story: April 2026 managed 223.1 hours of sunshine and just 4.8 mm of rain, while September 2026 got 147.8 hours and 26.2 mm (2026 figures still provisional). Spring dries a drive. Autumn takes patience.

Watch the joints, not the blocks. The surface can look bone dry while the joints are still dark with moisture underneath.

Permeable block paving needs different care

Some drives are built to let rain soak straight through them, with wider joints filled with open-graded grit rather than sand. The government's guidance on permeable front gardens describes them as surfaces with "open voids across the surface of the material or around the edges of blocks that allow water to soak in", and it warns against putting "soil, sand or similar material on the driveway that will block the surface and stop water soaking in".

Two things follow. First, if your drive is permeable, re-jointing with kiln-dried sand clogs the very gaps it drains through, so it needs the matching grit instead. Second, the cleaning itself matters more, because silt washed down into those voids chokes them. It's gentler work with the run-off controlled, not a flat-out blast.

The same guidance notes that laying more than 5 square metres of traditional impermeable driveway in a front garden has needed planning permission since 1 October 2008, unless the water runs to a permeable area. Worth knowing if a clean has you thinking about a full replacement.

Where the wash water goes

A block paving clean moves a lot of dirty water, with biocide and degreaser in it. That water should go to the foul drain, the one that goes to a treatment works, not the surface water drain at the end of your drive.

The Environment Agency's piece on drain misconnections explains why: one household system "carries wastewater from toilets, sinks and washing machines to a treatment works", while the other "carries rainwater from roofs and driveways straight to rivers and lakes". What goes down the wrong pipe "bypassing treatment entirely" ends up in the river.

On a professional job we control the run-off as we go. If you're doing it yourself, sweep the slurry away from the road drain and let it soak into a border or lawn instead, planting well wetted down first.

How long does a block paving clean last?

Honest answer: it depends on shade and trees, not on how hard it was washed.

• Open, sunny drive, re-sanded properly: 12 to 18 months before it starts to green again.
• Shaded drive, or one under trees: growth can be back in 6 to 9 months, because the surface never dries fast enough to discourage it.
• Either way: a stiff brush every few weeks and a spot-treatment at the first green film will stretch any clean by months.

Sealing pushes the intervals out further because the sand stays put and there's less for seeds to root in. What doesn't work is pressure alone on a wet autumn weekend, which is why so many drives look worse by Christmas than they did in September.

Clean it or replace it? An honest guide

Sometimes people ring us for a clean and the kind thing to do is talk them out of it. Cleaning makes a dirty drive look new. It can't make a failed drive sound again.

Cleaning is worth it when:

• The blocks are sound but the surface is green, black or stained. That's a cleaning job.
• The joints are empty but the blocks sit flat and tight. Clean, re-sand, compact, done.
• Oil stains are the main problem. Treatable in most cases, worst case a few blocks get lifted and swapped.

Replacement (or relaying) is the honest answer when:

• Blocks rock, sink or rut where the car sits. The sub-base underneath has failed, and no wash fixes that. The blocks can sometimes be lifted, the base redone and the same blocks relaid.
• The edges have spread. Broken edge restraints mean the whole field of blocks is creeping outwards.
• Blocks are crumbling or spalled. Water has got into them and frozen, or they've taken years of over-pressure washing.
• Half the drive is on different levels. That's groundwork, not cleaning.

We'll tell you which yours is from a couple of photos, free, before anyone books anything.

FAQ

How do you clean block paving without damaging it? Kill the weeds and moss first, then wash at medium pressure with a wide fan, the lance at about 30 degrees and a foot off the surface, working diagonally across the blocks. Never point a jet straight into the joints, and re-sand with kiln-dried sand once the drive is fully dry.

Do you have to re-sand block paving after cleaning? Yes, whenever sand has come out, which it will have. The jointing sand is structural: it locks the blocks and spreads the load of a car. Skip it and the blocks start to rock and shift.

Why does block paving grow so many weeds? Because the joints have lost their sand. Wind-blown dust and grit settle into the empty joints, seeds land in them, and each joint becomes a planter. Re-sanding, and optionally sealing, is what slows them down, not weedkiller alone.

How long should block paving dry before re-sanding? In summer, around a day. In autumn, allow 24 to 48 hours of dry weather and check the joints, not just the surface. Damp joints make kiln-dried sand bridge and stick instead of filling them.

Can you pressure wash permeable block paving? Carefully, yes, but it needs gentler work with the run-off controlled so silt isn't washed into the drainage voids. Re-joint with the matching open-graded grit afterwards, not kiln-dried sand, which would clog the surface it drains through.

Is it worth cleaning old block paving? Usually, yes. Green algae, black spot and weeds live in the joints and on the surface, not in the blocks, so a proper clean and re-sand makes a tired drive look close to new. If blocks rock, sink or crumble, that's a relaying job instead.

Get your drive cleaned and re-sanded properly

If the drive is green, slippery or losing its sand, send us a couple of photos and rough dimensions. We'll tell you straight whether it's a clean and re-sand, a few replacement blocks, or a bigger job, and quote the driveway cleaning and re-sanding with sealing as a separate, optional line. If it's a bigger job, we'll say so and point you at a groundworker rather than take your money for a wash that won't last.

Get a free, no-obligation quote, call us on 07375 104665, or message us on WhatsApp at wa.me/447375104665 for a same-day answer. We cover North London and the Hertfordshire borders.

Last updated: 7 October 2026

About Techno Clean: a London deep-cleaning company covering North London and the Hertfordshire borders. We specialise in one-off deep cleans, end of tenancy and after builders cleaning, fully insured with £5 million public liability cover and DBS-checked teams, rated 4.9 from over 180 reviews across 500+ completed jobs.