Patio and driveway paving
The most-asked outdoor cleaning question, and the manufacturer's own guidance spends more words on how NOT to pressure wash it than on how to clean it.
Precautions
- Wear gloves
- Wear eye protection
- Test on an inconspicuous area first
- Dispose of responsibly
Start here
What this is, what tends to go wrong with it, and what to do about it.
Made from
What tends to go wrong
Three different organisms treated as one green problem. Where they grow tells you more about the fix than any product does.
Why it is difficult: Moisture control and recurrence, Surface roughness
The stain where the trade guidance switches from water to solvent — and the switch brings a warning the water route does not have.
Why it is difficult: Why oil resists water, Penetration into fibres, Why old stains are harder
A seasonal particulate that is part of ordinary dust for most of the year and overwhelms it for a few weeks. Dry removal first, because wet pollen stains.
Why it is difficult: Why different surfaces get different dirt
- Algaevia its material
The green film outdoors, and NOT the same organism as the mould indoors. Where it grows is the diagnosis: shade, overhanging trees, or paving that does not drain.
Why it is difficult: Moisture control and recurrence
- Engine oilvia its material
Not simply an oil. Used engine oil carries combustion soot and metal particles, which is why it marks darker and behaves worse than the oil that went in.
Why it is difficult: Why oil resists water, Penetration into fibres, Why old stains are harder
- Road salt· no established method
A white tidemark on boots, carpet and car sills that is also actively corroding whatever it is sitting on.
Why it is difficult: Chloride attack, Evaporative deposition
- Bird droppings· no established method
Acidic, alkaline in places, and gritty. On vehicle paint in sun it etches within hours, and what remains after washing is a mark in the finish rather than on it.
Why it is difficult: Why old stains are harder, Coating thickness
The science behind this: Porous and non-porous surfaces, Water purity and aggressiveness
In detail
Almost everyone asking about a patio is asking one of two things: why it keeps going green, and whether the pressure washer will wreck it. The green is algae, moss or lichen, and where it grows is the diagnosis rather than the problem. The paving manufacturer names heavy shade, overhanging trees, and paving not laid to an adequate fall. That makes it a drainage and light question, which is why it returns after every clean. On the pressure washer the answer is a qualified yes with a geometry attached. Used to excess it shortens the paving's service life. The lance is never aimed straight down, because that lifts the jointing material out from between the units; it is held at no more than THIRTY DEGREES across the diagonal; and the joints are inspected and refilled afterwards, because empty joints are bad for the pavement itself. The routine the manufacturer leads with is the one most people skip: regular brushing, and an acid-free soapy wash where the colour has been masked, rinsed until all the soap has gone. Run-off matters outdoors in a way it does not indoors: hypochlorite will burn or kill plants, so borders are protected and the wash water goes to a drain.
Where the answer depends
Acetic acid (vinegar) requires the precaution Patio and driveway paving
Not established
Whether this is safe is not established by any authoritative source. That is not the same as it being safe — it means the evidence needed to answer has not been published. Do not treat this as permission to proceed.
THE CLEARANCE IS FOR ONE CONTAMINANT AND NOT THE OTHER. The paving manufacturer offers vinegar as a household remedy for RUST on its product, after a discreet test, and gives an entirely different route for organic growth. It is not offered for organic growth, and does not carry across.
Precautions
- Test on an inconspicuous area first
- Check the manufacturer's instructions
Evidence
Disputed
Sources
Cleaning & Maintenance Guidelines — Gardens & Driveways
Marshalls plc · Manufacturer documentation
Relied on for: That vinegar is offered as a household remedy for RUST marks on paving after a discreet test, and that organic growth on the same surface is addressed by an entirely different route. (states this directly)
Related
- Patio and driveway paving is made from Concrete and stone paving
- Patio and driveway paving is commonly affected by Moss and lichen
- Patio and driveway paving is commonly affected by Oil and grease on textile
- Patio and driveway paving is commonly affected by Road salt
- Patio and driveway paving is commonly affected by Pollen
- Patio and driveway paving is commonly affected by Bird droppings
Hacks and claims involving this
- Jet-washing the patio every spring Supported
Sources for this page
Sources
Cleaning & Maintenance Guidelines — Gardens & Driveways
Marshalls plc · Manufacturer documentation
Relied on for: That organic growth is prevalent in heavy shade, under trees or where paving is not laid to an adequate fall, that the power lance is held at no more than thirty degrees across the diagonal and never directed down because that loses jointing material, that joints are refilled after washing, and that sodium hypochlorite will burn or kill plants. (states this directly)