Patio cleaning: which method suits which surface?

The first instinct when a patio has turned green is to reach for the pressure washer. On some surfaces that is exactly right; on others it does more damage than the dirt ever did. What decides which method is an option is the surface material — not how dirty it is.

Concrete slabs and concrete paving

The most robust case: concrete slabs and concrete paving take cold-water as well as hot-water high pressure. What matters is what happens afterwards. The jointing sand is washed out along with the dirt and has to be brushed back in once the surface is clean. If that is forgotten, the surface settles over the years and weeds have an easier time in the open joints — the most common mistake when people clean a patio themselves.

Natural stone

Natural stone is not a single category, and blanket recommendations are misleading here. Hard natural stones such as granite are considerably less sensitive than soft, porous ones such as sandstone. On soft stone, too much pressure can roughen the surface — after which dirt takes hold faster than it did before. So for these surfaces: lower pressure, more distance, and if in doubt a test patch in an inconspicuous spot before the whole patio is worked on. Which methods exist at all, and where their limits lie, is covered in more detail in Cleaning paving and natural stone: high pressure, steam or by hand?.

Wood

On wood, high pressure tears the fibres open. The effect is treacherous because it cannot be seen straight after cleaning: the patio looks clean and then greys faster than before, because the roughened surface holds moisture and dirt better. The gentle option is the right one here — a brush, a cleaning agent suited to the surface, and working along the grain. Whatever the manufacturer specifies for that particular timber always takes precedence.

WPC and composite materials

With WPC and similar composite materials much the same applies as with wood, but for a different reason: the plastic content can be damaged at the surface by too much pressure or water that is too hot. The structure then goes dull and blotchy, and that cannot be undone. Because the composition differs from product to product, the manufacturer’s specifications are the binding basis here — not what worked on the neighbour’s patio.

How often does a patio need cleaning?

That depends above all on the position and the aspect: shady, damp areas under trees need freshening up every 1–2 years, while sunny, well-ventilated spots often manage 3–5 years without. Preventing regularly is almost always cheaper than restoring occasionally — fresh green growth comes away with far less effort than moss that has been growing in for years. When a cosmetic problem turns into a safety one is described in Algae, moss and green growth on patios and footpaths: when does it become dangerous?.

What does a patio clean cost?

Pricing is generally worked out per square metre. How high that square-metre price turns out to be comes down to four things:

• Area: the most important factor — larger continuous areas can be worked more economically than small, awkwardly shaped ones.
• Degree of soiling: a light green film comes off faster than ingrained moss, where the joints need follow-up treatment as well.
• Material: wood and WPC call for the more laborious gentle method; robust concrete paving does not.
• Access: roof terraces, narrow carriage entrances or long runs for hose and machine all add to the work involved.

For a wider view of what determines the price of stone cleaning, see Stone cleaning: when is it needed, and what does it cost? — which also points you to the price calculator.

How Zamsa goes about it

We choose the method to suit the surface rather than out of habit — the check happens before the first move, not after it. On request we clean a test patch in an inconspicuous spot beforehand, so you can judge the result once it is dry and before the whole patio is done. And the jointing sand is brushed back in after cleaning. What else is included is set out on our page on stone cleaning.