Patio cleaning cost depends heavily on size, surface type and how bad the black algae spotting has got, so a single flat rate rarely tells the whole story. Most homeowners searching this are trying to work out a realistic budget before booking.
Below are size-banded price ranges, an explanation of why black spot algae often carries a surcharge, and what re-sanding the joints typically adds.
Patio cleaning prices by size
For a small patio, roughly up to 20m², expect £80-£150. A medium patio around 20-40m² typically runs £150-£280. A larger patio or one combined with a path and driveway area over 40m² can reach £280-£450+, especially with heavy algae or moss in the joints.
Natural stone (sandstone, York stone) and concrete flags price similarly, though porous natural stone with deep black spot staining sometimes takes longer to treat properly and can push toward the higher end of a given size band.
Why black spot algae adds to the cost
Black spot is a particularly stubborn lichen that bonds tightly to stone and doesn't lift with a standard pressure wash alone. It needs a specific chemical treatment applied before or alongside cleaning, and sometimes a second visit once the treatment has had time to work. Firms that quote a flat low price often haven't accounted for black spot, and either skip it (leaving the patio still spotted) or add a surprise charge on the day.
If your patio has the tell-tale small black or grey-black rings, especially on sandstone, mention it when you get a quote so it's priced in properly from the start rather than becoming an on-the-day add-on.
Re-sanding costs
Pressure washing a patio inevitably disturbs some of the jointing sand or old pointing between slabs, and a thorough clean often washes weeds and moss out of joints that then need refilling. Re-sanding with kiln-dried sand typically adds £3-£6 per m² on top of the clean, or a flat £50-£150 depending on patio size, and it's worth doing since empty joints let weeds and moss straight back in within a matter of weeks.
Some firms include basic re-sanding as standard on a full clean; others treat it as an optional extra. Ask which applies before booking so there's no surprise line item at the end, and check whether the sand used is a proper kiln-dried product rather than ordinary building sand, which washes out far more quickly.
Getting an accurate patio quote
Because black spot, joint condition and slab material all change the time a job takes, the most reliable quotes come from a look at the patio itself, either in person or from good photos showing the joints and any staining close up. A flat online price for 'any patio' rarely reflects what a specific garden actually needs.
It's also worth asking whether the quote includes clearing plant pots, furniture or a small amount of garden debris from the patio surface before cleaning starts, since some firms expect the area to be cleared in advance and others will happily move light items themselves.
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