Phosphating - is it the best method of surface preparation before powder coating?

In the introduction, we will not try to invent a definition of phosphatisation from scratch, but will refer to the definition in Wikipedia ( "Phosphatisation is the process of chemically or electrochemically producing a protective matt grey coating of phosphates on the surface of metals (mainly steel); carried out in hot solutions of phosphate and phosphoric acid." Phosphatisation (another name for phosphating) is applied prior to powder coating and aims to prepare the surface in such a way that the paint provides effective surface protection against the weather. Obtaining a durable, low-porosity anticorrosive surface is not the only application of phosphating. The process is also used to facilitate cold forming (e.g. stamping), as a friction-reducing layer and even for electrical engineering purposes as an insulating layer.

What are the advantages of phosphating?

There is no denying that phosphating has a great many advantages, of particular importance to painters. Among these are: corrosion resistance, improved adhesion, degreasing and the removal of chemical impurities. It is a widely used and well-known process and, with all the requirements, the conversion coating obtained is of good quality. The question that arises is whether it is the optimal process to prepare the surface for powder coating?

Disadvantages of phosphatising

Phosphating is a complex process that requires space for it to run properly due to the successive washing, rinsing and draining stages. Pre-washing agents, additives to improve washing, additives to correct the pH, products to form a conversion coating, possibly fluoride additives (treatment of aluminium and zinc), often toxic, are used for this process, and the whole process requires constant control of the operating parameters. Phosphating requires demineralised water. If, due to surface constraints, limited personnel, sludge formation, there are minor errors in this complex process, the result is problems in the quality of the conversion coating, which affect the quality of the paint finish. And that's not all.

Energy costs

In previous offer publications sent to customers, we did not place as much emphasis on the energy intensity of the phosphating process. However, following recent increases in energy and gas prices, we have to point out that phosphatising requires an alkaline pre-wash temperature of more than 50°C. At present, this is a noticeably energy-intensive element in the process surface preparation for powder coating.


Is phosphating the best way to prepare a surface for powder coating? To answer this question, we will use a simple car analogy. When washing and protecting your car, do you use the proverbial Ludwik liquid, or do you use modern chemicals in the form of bloody rim, tar and rubber removers, and apply ceramic coatings to the paint? Likewise with phosphating. It is a process that has worthy successors in the form of chemicals that are easier to apply, require lower temperatures and generate savings at every stage of surface preparation for painting. Kairos has a range of chemicals, the use of which we discuss during a free consultation, and we support each implementation with our knowledge and experience. Detailed comparison of the Kairosurf technology and the phosphating process we presented in a separate entry.