Cleaning paving and natural stone: high pressure, steam or by hand?

Not every cleaning method that works on concrete is also suitable for natural stone or jointed paving — used wrongly, a pressure washer soon does more damage than it puts right. An overview of the common methods and when each one is the right choice.

Why the choice of method decides the outcome

Surfaces such as interlocking concrete block paving, natural stone (sandstone or granite, for example) and jointing material each react differently to pressure, heat and chemicals. Water pressure that is too high from too short a distance can wash out the jointing sand, roughen the surface of soft natural stone or damage an existing seal — with the result that dirt and algae then take hold again even faster.

The three common methods compared

• High-pressure cleaning: fast and effective on robust concrete paving, but only with the pressure adjusted (well below the maximum pressure of standard machines) and enough distance from the surface.
• Steam cleaning: gentler, working with heat instead of high pressure — well suited to more delicate natural stone surfaces and to heavily used areas such as entrances.
• Cleaning by hand with brush and cleaning agent: more time-consuming, but the gentlest method for historic or particularly delicate natural stone, as well as immediately next to planting and lawns.

Typical mistakes that cause damage

• Holding the lance too close to the surface (rule of thumb: at least 20–30 cm, depending on the machine and the surface)
• Cleaning jointing sand at too high a pressure, without re-filling the joints afterwards
• Using aggressive cleaning agents on lime-bearing natural stone (which can cause irreversible etching or staining)
• Cleaning in full sun, which makes cleaning agents dry too quickly and leave streaks behind

After cleaning: sealing as protection

A professional clean lasts considerably longer if the surface is sealed or impregnated afterwards — that makes it harder for algae, moss and dirt to take hold again, and so also reduces the cleaning effort needed the following year. Why some surfaces turn green again so quickly in the first place is covered in our article Algae, moss and dirt on paving and façades — causes and prevention.

How Zamsa helps

Before every job we first check the material and the degree of soiling, and only then decide on the method. We mostly work with hot-water high pressure: the heat penetrates moss and algae more deeply than cold water, so the pressure can be kept lower and the joints and the stone surface are treated gently. Delicate spots and the transitions to beds and lawns are finished off by hand. What is included is set out on our page on stone cleaning.