Why should the metal be primed before painting?
Primer directly determines how strong will be the layer of paint that you put on the metal. It promotes good adhesion of the paint and the surface itself. In addition, it performs another significant and important role - protection against corrosion and rust. After all, metal products often fail because of it.
To minimize metal damage, it is necessary to perform the whole complex of protection. Some types of primers are so-called rust converters. It is coated with a metal that has already been corroded to extend its life.
Priming for metal surfaces is divided into several types: insulating, phosphating, passivating, protective, inhibiting and rust converters. Let's consider each more in detail.
types of primer for metal The insulating film forms a film that protects the surface from moisture and oxygen. Usually zinc white, iron rosary and fillers are added to it. The most common are alkyd primer for metal GF-021 and epoxy EP-0010.Apply it mainly to ferrous metals. Advantage can be considered its low price.
Phosphating is used for non-ferrous and ferrous metal surfaces. It makes it easier to passivate the metal, phosphate it and increase adhesion. Usually it is called a two-component, since it contains a base and an acidic diluent with orthophosphoric acid.
It also has one more name - zinc primer, because it can be painted with galvanized steel, to which the majority of paint and varnish materials do not have adhesion. But the final coating can be any enamel. Such can be VL-02 and VL-023.
Passivating reduces the electrochemical activity of the metal, significantly slows down corrosion. Water, which gets to the metal through the coating, dissolves some of the pigments contained in the layer. Representatives of this type are the primer FL-03K and GF-0119.
Protector contains up to 90% of metal pigments( zinc-magnesium alloy, zinc powder and lead).When interacting with the electrolyte, the paint and varnish composition with zinc powder forms a dense impermeable film under the action of corrosion.
Epoxy-polyamide compounds, alkyd-styrene resins are used for film formation, etc. If a scratch occurs on the paint coating, the zinc particles protect the metal, acting as a tread.
It is good to use it for corrosion protection of steel surfaces that are in seawater. Such are the primer XS-068, EP-057 and EP-0284.
Inhibiting primer has become very popular lately. Corrosion inhibitors not only increase protection, but create a new kind of material - primer-enamel. They combine the advantages of these two substances. Corrosion inhibitors have two types: oil-soluble and water-soluble. Issued such a brand as EP-0180.
rust converters are used on the surface with which rust or scale has already been removed. Primer for rust in its composition has orthophosphoric acid. It converts corrosion into insoluble iron phosphates. Simultaneously with the transformation of rust, the surface acquires a polymer film, which makes the coating resistant to corrosion. The compositions of this action can be called EP-0199 and ХВ-0278.
How to choose a primer for metal and how to apply it?
It is worth taking into account several factors when choosing a primer:
- which metal is processed;
- in what conditions will be used( aggressiveness of the environment, climatic conditions, mechanical loads);
- type of substance that forms the film.
After selecting a primer, you can start surface treatment. The first thing you need is to check the existing layer of paint. To do this, make two notches, glue the tape between them and tear it off sharply. If the paint comes off, then it must be completely removed.
Next you need to clean the surface of rust and other contaminants. After these procedures, you can begin to apply a primer a thin layer. Do this with a roller, brush and spray gun.
If the surface is glossy, then it needs to be scraped with fine-grained emery paper for better adhesion to the paint. And only now you can start applying a coat of paint.