How to clean different metals well – a quick guide

In order to get a high-quality painted surface, you need to take care of its cleanliness. Indeed, often the cause of many defects is insufficient cleaning and neglect of the surface degreasing stage. Some metals go through specific shaping steps that will prevent paint from adhering without proper pre-treatment. The most common compounds that spoil the quality of the coating are waxy residues, oily stains, vegetable or animal fat stains. They act as a certain insulator between the polymer material of the powder paint and the metal. There is no way to avoid their influence, since fatty compounds contain special substances that are used during rolling, processing and forging of metal parts. Some are treated to prevent rusting.

But powder paint should only be applied to a clean surface. When choosing cleaning methods, it is important to consider the material of the product, the processes that were used in its creation, grinding, processing, etc. After all, there is a tool for every pollution and there is no single universal and economical cleaning method.

There are both mechanical and chemical methods for removing dirt from metal surfaces. All of them are used for certain types of metals and their characteristic contaminants:

Hot rolled steel

The most common problem with this type of metal is precisely dross. It forms on the metal surface due to oxidation of the top layer. It is such rust, no more than 1 mm thick. This process is absolutely natural. An oxide layer forms on the surface and protects the product from further corrosion, but outwardly it is not smooth and looks very untidy. In addition, everything is accompanied by residues of soot, grease and dust. In order to remove the rust layer from the surface, sandblasting is necessary. This is a fairly economical method. Also, in this way, the remains of old paint are removed. Sandblasting improves the surface and makes it smooth. And in the fight against foreign substances and dirt, degreasing with alkalis and orthophosphoric acid will help.

Cold rolled steel

The same contamination is typical for cold rolled steel. Oil stains often appear on it, as well as corrosion inhibitors. These are special substances that prevent the metal from rusting during its formation, but at the same time they negatively affect the adhesion of the paint to the surface. To avoid this, alkaline cleaning and phosphoric acid cleaning should be used before powder coating.


Stainless steel and galvanized steel

Stainless steel and galvanized steel do not require cleaning from anti-corrosion materials, but after working with these alloys, dust, oils from processing equipment, as well as a thin layer of passive oxides remain on the surface. It may be quite unnoticeable at first, but it’s worth remembering that high quality stainless steel also reacts with oxygen. Such contamination will require sandblasting, alkaline cleaning and rinsing.

Extruded metal

Its peculiarity is that the molten material is squeezed through the matrix to form metal rods, pipes or any other elongated objects. Usually, aluminum performs better in this technology, since it is more malleable to change and formation. However, you have to use special anti-corrosion agents. Then they need to be cleaned in several stages – alkaline cleaning and cleaning with phosphoric acid, chromate treatment, and then powder coating. The process is multilevel, but really worth it. Such products serve for a long time and do not lose their attractiveness for many years.


For cast aluminum and zinc products, sandblasting is essential. It will remove any remaining dirt. Polishing may also be necessary to remove traces of the fasteners and, last but not least, degrease the residual oils with phosphoric acid.

As we can see, the preparation process is not so much difficult as it is very troublesome. It is worth taking into account all the nuances and keeping track of which methods are best to deal with certain contaminants. Let all of the above serve as a reminder of the importance of cleaning and degreasing the surface before painting, and also be a little cheat sheet on the correct cleaning methods.


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