How Often Should You Jet Wash a Driveway?

Twelve to twenty-four months covers most drives. That range is wide because the factors that decide it vary enormously between two houses on the same street.

Here is how to work out where yours sits, and a better test than any interval.

The better test

Forget the calendar. Go and stand on it in November, when it is wet.

If it is slippery underfoot, it needed doing in September. Algae becomes genuinely hazardous before it becomes visually offensive, and a green north-facing drive in winter is the most likely place on a property for somebody to fall.

If it is not slippery and you are just not keen on the colour, you have time.

Aspect is the biggest single factor

Which way your drive faces matters more than anything else on this list.

A north-facing drive gets little or no direct sun through the winter half of the year. Surfaces stay damp for most of the day, and damp is what algae needs above all else.

A south-facing drive in the open dries within an hour or two of rain for much of the year, and direct sun is actively hostile to algae.

The difference is not marginal. A north-facing drive might need doing annually. The equivalent south-facing drive in the same street can go three years.

If your drive is partly shaded, it will go green in the shaded strip long before the rest, and it needs doing on the schedule of its worst section.

Tree cover

Trees do three things, all unhelpful.

They block sun, which extends the damp period.

They drop leaves, which sit on the surface holding water against it, and leach tannins into porous paving leaving brown staining that is a different problem entirely.

They reduce airflow, which slows drying further.

A drive under a mature tree is roughly on a twelve month cycle. The same drive in the open might be on thirty.

Coastal exposure

If you can see the sea, you are on the shorter end.

Salt in the air is hygroscopic, meaning it absorbs and holds atmospheric moisture. A salted surface stays damp longer after rain and picks up dew earlier in the evening, which extends the growing conditions for algae well beyond what the rainfall alone would suggest.

Around Seaford, Peacehaven and the exposed clifftop properties, twelve to eighteen months is realistic. A sheltered drive a couple of miles inland at the same latitude will go noticeably longer.

The ground underneath

Free-draining ground helps. Chalk, which is most of the coastal strip here, drains fast and the sub-base under your paving dries out.

Clay does not. Weald clay holds water, so paving laid on it keeps drawing moisture from below long after the surface looks dry. The inland towns north of the downs are on a shorter cycle for this reason alone.

A high water table does the same thing, which is why low-lying areas need doing more often.

Surface type

Porous surfaces are worse than dense ones, because the growth gets into the material rather than sitting on it and cleaning does not remove all of it.

Soft natural sandstone is the most porous common paving. Concrete block is moderately porous. Porcelain is almost completely non-porous, which is why porcelain patios stay clean far longer.

If your drive greens up again within months of a proper clean, porosity is usually why, and sealing is the thing that changes it.

Putting it together

Work through the list and count.

Shorter interval, roughly annually: north-facing, under trees, coastal, on clay, porous surface. Any three of those and you are on a yearly cycle.

Longer interval, two to three years: south-facing, open, inland, free-draining, dense surface.

Most drives sit between the two, which is where the eighteen month figure comes from.

What changes the interval

Two things genuinely extend it.

A biocide treatment after cleaning kills the spores left in the surface rather than just removing the visible growth. At £1.50 a square metre it typically buys an extra year, and it is the best value item on my price list for a shaded or coastal drive.

A joint-stabilising sealer on block paving keeps the sand in the joints and denies weed seed a footing. It roughly doubles the interval, at a cost of £7.50 a square metre.

One thing that does not: cleaning it harder. Turning the pressure up removes more block, not more algae, and a roughened surface then holds dirt better than it did before. You will need me sooner, not later.

The case against doing it too often

Every clean takes a small amount off the surface. That is unavoidable, even done carefully.

Washing a drive annually when it does not need it will visibly age it over a decade, and on block paving it means the joint sand is being disturbed far more often than it should be.

If your drive genuinely stays clean for two years, leave it for two years. There is no maintenance benefit to cleaning paving that is not dirty.

The seasonal answer

If you want it done for spring, book in February. Demand rises sharply from the middle of that month and by April most of us are working several weeks out.

If you want it done cheaply and you do not care when, ask in November or January. That is when the diary has gaps.

A rough scoring method

If you want something more concrete than “it depends”, score your drive out of six. One point for each of these that applies.

North-facing, or shaded for most of the day.

Overhung by trees, or with a hedge along one side.

Within a mile of open water.

On clay, or somewhere water stands after rain.

Porous surface: natural sandstone, older concrete, local soft stone.

Never treated with a biocide.

Five or six points means annually. Three or four means every eighteen months. One or two means every two to three years. Zero means leave it alone until it looks like it needs doing.

It is not science. It is the mental arithmetic I do standing on somebody’s drive, written down.

Between cleans

Three things that are free and make a measurable difference.

Sweep it. Leaf litter and silt hold moisture against the surface and give algae a growing medium. Twenty minutes in November is worth more than most products.

Clear the gaps and gullies. A blocked gully means standing water, and standing water means the worst growth on the drive will be in that spot.

Cut back what shades it. Two extra hours of winter sun on a drive changes its drying behaviour materially, and it is the single most effective thing available to most people.

What I would not bother with: household bleach, which kills what it touches and does nothing afterwards, can lighten paving unevenly, and should not be going into a border or a drain. Salt, which actively makes things worse because it holds moisture. Washing-up liquid, which leaves a residue that attracts dirt.

If you want a between-cleans product, buy a proper exterior biocide and follow the dilution.

Doing it more often than necessary

Every clean takes a small amount off the surface, however carefully it is done, and on block paving it disturbs the joint sand.

A drive washed annually when it only needed doing every three years will look visibly older after a decade than one washed on a sensible interval. That is a real cost and it does not show up until it is too late to do anything about it.

The test at the top of this article is the honest one. Slippery in November means it needed doing. Merely not as bright as it was in 2019 does not.