Cleaning, and the
part everyone skips.
Washing a patio takes an afternoon. Re-jointing it afterwards is what stops it looking the same again by spring.
A dirty London patio is usually not dirty. It is biological: algae, lichen and moss growing in a damp, shaded, low-airflow space, feeding on organic film from leaf fall and pollution. That is why it comes back so quickly after a wash — the pressure washer removes the growth but nothing about the conditions that grew it.
It is also why pressure alone is the wrong tool used on its own. A lance held too close, or a turbo nozzle used on the wrong surface, erodes the face of natural stone, furs up the surface of concrete block so it holds dirt more readily than before, and blasts the jointing straight out from between the units. A surface cleaned aggressively once is measurably faster to re-soil, because the surface texture has been opened up.
The work that actually changes the outcome happens after the washing. Once the joints have been cleaned out — and they always are, to some extent — they have to be refilled: kiln-dried sand for block paving so the interlock is restored, or a brush-in jointing compound for slabs. Paving without joint fill loses its structural interlock, lets water into the bed and grows weeds along every line. Re-jointing is the step most often left out, and it is the one that decides whether the surface still looks clean next year.
What the work involves
- Rotary surface cleaning
- A flat-surface head rather than a bare lance. It cleans evenly and does not cut the tiger stripes into stone that a lance leaves.
- Biocide treatment
- Kills the algae and lichen at the root. Pressure alone removes what is visible and it returns within months.
- Re-sanding joints
- Washing strips jointing sand out. Left unfilled, blocks work loose and weeds return — so joints are refilled as part of the job.
- Sealing
- Worth it on porous sandstone and limestone against oil and staining. Unnecessary on porcelain, which does not absorb anything.
How it is built
- Protect the plantingBeds and borders covered before anything is sprayed, and treatments chosen to be safe around them.
- TreatBiocide applied and left to work, rather than blasting first and hoping.
- WashEven passes with a rotary head, at a pressure the surface can take — soft sandstone and hard granite are not cleaned the same way.
- Re-sand and settleJoints refilled and vibrated where the surface is block paving.
- Seal if specifiedOnly once the surface is fully dry, or the sealer traps moisture and clouds.
What decides the approach
The things that change the answer on a London job — and that nobody can judge from a brochure.
The surface decides the pressure
Natural sandstone and old concrete are soft and erode under a turbo nozzle. Granite and porcelain take far more. Block paving cleans well but loses its sand every time. The setting is chosen from the material and its condition, not turned to maximum by default.
Re-jointing is the actual job
Kiln-dried sand restores interlock in block paving; a brush-in compound refills slab joints and resists weed growth. Skipping it leaves the paving structurally looser and dirtier faster than before it was cleaned.
Where the run-off goes
Wash water carries silt, biocide residue and hydrocarbons. It should be directed to a foul drain or a soakaway, not flushed into a surface-water gully that discharges to a watercourse. On a driveway this is a genuine pollution issue rather than a technicality.
Treating the growth, not just removing it
A biocide applied after cleaning kills the spores the wash left behind and substantially lengthens the interval before regrowth. Washing alone leaves a fully viable root system in the joints and the surface pores.
Shade, airflow and why it came back
North-facing, enclosed, overhung by a neighbouring tree — that combination regrows algae within months whatever is done to it. Sometimes the honest recommendation is thinning the canopy or improving drainage rather than washing more often.
When cleaning is the wrong answer
If slabs rock, joints have opened along a line, or a low area holds water, the base has moved. Cleaning it makes a failing patio look better for a season while the actual fault continues. That is a lifting-and-relaying conversation, and it is worth having honestly.
What it costs
Every garden is priced from its own survey, because the cost is decided by things that are invisible until the ground is opened: how far the spoil has to be carried, what the existing sub-base is made of, whether levels have to be built up or cut away, and how the site drains. We quote after measuring, not before.
Book a free site surveyJet Washing & Rejuvenation, answered.
How often should a patio be jet washed?
For most London gardens, once a year is enough if the joints are refilled and a biocide is applied afterwards. A shaded, north-facing or tree-overhung terrace regrows faster. Washing more frequently than needed is counterproductive on soft stone, because each aggressive clean opens the surface a little further.
Can jet washing damage paving?
Yes. Too much pressure, or a turbo nozzle held too close, erodes soft sandstone and old concrete, furs up block paving so it holds dirt more easily, and strips the jointing out. The pressure is matched to the material — the damage is not usually obvious on the day, but the surface re-soils noticeably faster.
Does the sand need replacing after cleaning block paving?
Always. Block paving works by interlock, and that interlock depends on sand filling the joints. Washing removes it, so the blocks are left free to move, water gets into the bed and weeds germinate along every line. Re-sanding with kiln-dried sand is part of the job, not an extra.
Why does the green growth come back so quickly?
Because the wash removes the visible growth but leaves spores in the surface pores and joints, and it does nothing about the shade and damp that let them grow. A biocide treatment after cleaning kills what was left behind and pushes the regrowth back substantially.
My patio is uneven as well as dirty — will cleaning help?
No. Rocking slabs, joints that have opened along a line and areas that pond water are all signs the base beneath has moved or was never deep enough. Cleaning improves the appearance for a season while the underlying fault carries on. That surface needs lifting and relaying, not washing.
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