How do I prepare the metal surface before powder coating with a Karcher pressure washer?

Karcher pressure washers are used very frequently in industrial practice. They are present where the capacity of the paint shop does not justify the investment in a fully automatic washing line or the parts to be washed would not fit in the washing booths or tunnels.


Surface preparation of metals consists, in the first instance, of the removal of all types of contamination from the surface of the parts which could adversely affect the adhesion of the powder coating. These include oil impurities (degreasing) and oxides of these metals. This is especially important for aluminium and galvanised parts. After washing, the chemical reacts with the surface of the metals to form a so-called conversion coating. This increases the adhesion of the paint and improves corrosion resistance.

Technical solutions

Typically, the washing and conversion coating (passivation) process is carried out on special stations.

The workpieces are placed in drip trays and then pressure washed. The washing solution is returned from the tray to the main tank. From there, usually by gravity, it is delivered to the Karcher.

After washing, it is necessary to rinse the elements with water.

With this approach, the washing solution can be used over a longer period of time. However, nothing is forever and the bath will eventually become saturated with contaminants and washed-off oil.

It also happens that users use chemical dosing systems installed on Karcher pressure washers. In this case, once the desired working concentration is set, the system itself dispenses the correct amount of concentrate and mixes it with water before feeding it onto the spray lance.

There is then no main tank in which the bath is collected.

The downside of this solution is that the solution is used once and goes straight to disposal after washing.


Phosphating problems

The most common type of chemical for cleaning and surface preparation (passivation) is iron phosphating. However, it has its shortcomings when it comes to operation:

- high operating temperatures - above 65 ºC

- formation of sludge and deposits - these block pipes, nozzles and boilers that heat the working bath.

It is very common for Karcher pressure washers to work in rotation - one is under repair due to sludge and the other is still washing. The cost of such repairs can be substantial - the cost of the Karcher coil alone averages £1,000 net.


The alternative to phosphating - Kairo-SURF chemistry in high-pressure cleaning


Kairo-SURF products are a viable, working alternative to traditional phosphate chemistry.


Low operating temperature - 25-30 ºC

  • Effective washing at almost ambient temperature reduces costs from bath heating.
  • Reduced evaporation improves the working environment.

No deposit formation

  • Kairo-SURF products do not contain phosphates. For this reason, there is no build-up of deposits in pressure equipment and no blockage of nozzles, lines or boiler faults.

Washes all materials

  • Kairo-SURF products wash and apply a conversion coating (passivate) to steel, galvanised steel, aluminium alloys, aluzinc.
  • Do not form white tarnish on aluminium


Low operating cost

  • Typical working concentrations are 5-7 grams / litre of bath. Over 4 x lower concentrations than competing products.
  • They work in the same pressure ranges as traditional chemistry.
  • To speed up the drying process, water of about 50 ºC can be used for rinsing.


No need for additives

  • Our products are ready to use without additional measures. Simply dilute them with water to a concentration of 5 to 7 grams / litre.
  • There is no need to carry out pH correction with NaOH solutions - our solutions are self-buffering, meaning that the pH stabilises itself at a certain level.
  • There is no need for special additives to improve cleaning properties.