Sustainable Building

Effective graffiti removal

In many cities, graffiti is a serious public nuisance. Daniel Took, Head of Professional Product Marketing at Kärcher UK explains four of the most effective ways to tackle graffiti and leave surfaces looking like new.

Particle blasting procedures – for stubborn dirt

Particle blasting is used when stubborn dirt, such as graffiti, has to be removed gently.  The procedure uses an air flow (compressor with a minimum output of 4 m³ per minute) to which precisely dosed spray agents are added. By selecting the appropriate type and quantity of spray agent, as well as air pressure, the procedure can be adapted for different surfaces.

There are around 2,000 types of spray agent available on the market, ranging from blast furnace slag to chalk and glass powder, as well as calcium carbonate. The differences are not just down to the output materials used, but also the size, shape and hardness of the grain. Dust is largely prevented by adding water at the nozzle (“damp blasting”) which has the added benefit of binding the spray agent and removed pigments in the water.

Flexible injector blasting systems

Injector blasting systems have proven to be extremely flexible, as they are easily transported in a case and have short set-up times, making them particularly effective for graffiti removal, as graffiti can often only be dealt with at individual points, rather than over a large area.  It can be used as one-man operation and is very adaptable. All parameters – air flow and air pressure, water flow and spray agent volume – can be set by the operator on the trigger gun according to the level of dirt and the surface being cleaned. This means that the operator can quickly switch the type of spray agent being used, from very gentle to very abrasive.

Injector blasting offers the following advantages:

  • easy transport and short set-up times
  • high adaptability
  • versatile
  • environmentally friendly
  • low operating and investment costs
  • safe handling

In order to be able to precisely determine costs and area performance, it is always advisable to carry out a test clean on-site.

High-pressure cleaning

High-pressure cleaners are a popular choice. The type and level of dirt will dictate whether cold or hot water machines are used. There is a trend towards using hot water machines, as the higher temperature makes greasy and oily dirt easier to remove, as well as lighter graffiti. Additional benefits of the hot water machines are a reduced cleaning time of up to 40% and that less cleaning agent is required, sometimes even none at all.  Drying times are also reduced so that next steps can get underway more quickly.

Water flow, too, is an important factor when selecting a machine, as it is crucial for impact pressure, which generates the cleaning action and aids the removal of the dislodged dirt.  The type of nozzle, spray angle (a 40° nozzle is normally used) and spray distance are also extremely important.

Dry ice blasting

While still a relatively new cleaning method, dry ice blasting is gentle, effective and has a wide range of uses, including grease, oils, adhesives, binders and silicone. It is also non-corrosive and virtually non-abrasive, which means it can be used on sensitive surfaces. Dry ice blasting is recommended when other cleaning procedures are prohibited by legal regulations, or if these methods would not be successful or could only be used with considerable investment of time and at great expense. However, this method does require consideration, as the technology is more costly.

Dry ice particles are ejected from the trigger gun with a compressed airstream up to the speed of sound and sublimate immediately upon contact with the surface being treated. They take effect in three main ways:

  • Ejected particles release their kinetic energy upon impact.
  • The layer being removed cools suddenly upon contact with the –79 °C ice, becomes brittle and cracks.
  • Some of the frozen carbon dioxide penetrates into the cracks of the encrusted dirt and paint layers and sublimates, thereby increasing its volume by a factor of 400, and causing the dirt to split off completely at a microscopic level.

The dirt is dislodged without the use of high pressure or water and falls off the surface.  As the dry ice turns into a gas upon impact, no residues are left.

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