A Primer On Epoxy Zinc Rich Primer Coating

By Author: protexion LLP
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Epoxy Zinc Rich Primer Coating has the advantage of healing moisture levels faster and independently than the healing efficiency of zinc-rich silicate primers. They also have good surface tolerance.

The primer is the most important layer of the coating as it acts as the base of the specified top coating needed to prevent rust. It also provides an after layer to hold the surface, thus enabling the subsequent coating films to stick properly. Therefore, the primer contains the binders needed to stick to the substrate and form the next coating system layer.

Since the primer is to fill and hide impurities on the surface of the substrate, it must be carefully matched to the surface features such as porosity. If parts of the top coat are damaged or later, the zinc content in the primer will continue to provide corrosion protection for a limited period of time.
Basics of Epoxy Zinc Rich Primer Coating
Epoxy Zinc Rich Primer Coating belongs to the family of zinc-containing coatings that are applied to prevent corrosion on iron surfaces. These primarily serve as single cathodic protection products. Since zinc ...
... is anode to steel, these particles rust first, preventing the iron layer beneath the primer from rusting.

The zinc product is powdered zinc oxide which exposes the remaining zinc coating to further oxidation, providing a protective consistency. Therefore, zinc-based primers offer sacrificial cathodic protection for steel substrates.

Reduced zinc epoxy primers contain approximately 55% zinc by weight, while zinc-rich epoxy primers contain approximately 80 to 85% zinc by weight.
Organic Versus Inorganic Epoxy Zinc Rich Primer Coating
Epoxy Zinc Rich Primer Coating is an organic coating and requires a top coating for durable and reliable heavy-duty protection. It can be applied with an airless spray, air spray, roller or brush - and the simplicity of application as well as the durability of the surface make it suitable for onsite maintenance applications. However, excessive use of primers containing organic zinc can cause cracks, which can lead to coating failure. Failures often appear on welds and corners.

On the other hand, primers containing inorganic zinc have the advantage of not requiring a top coating. In this case, silicate is usually used as a binder. This primer cannot be applied to the site, as it is very important to create the right surface by abrasive blasting of the surface. (For more information on this topic, see Surface Preparation for Inorganic Zinc Silicate Coatings.)

There are four major differences between organic and inorganic zinc-containing primers:
Binder. Organic forms use epoxy, butyl, urethane or other organic resins, while inorganic zinc coatings usually use zinc silicate binders.
Display temperature. Inorganic zinc can work at high service temperatures (up to 400C), while organic or epoxy zinc is known to work at low temperatures (up to 120C).
Lifetime service. Inorganic zinc has a longer service life than organic zinc. In marine environments, for example, inorganic zinc can last up to 15 years - while organic zinc has a service life of 13.5 years.
Resistance to friction, sunlight and solvents. Inorganic zinc is also known to be more resistant to organic zinc.
The Protection Mechanism of Zinc Rich Primers
Although the effective performance of zinc-rich primers is primarily attributed to corrosion prevention, the complex protection mechanism needs to be fully understood.

Initially, once the zinc-rich primer and top coating are applied as a continuous layer on the substrate, the coating system works. The corrosive environment can be termed as a barrier and aptly as a barrier coating. The coating completely separates the layer from the atmosphere.

Only after a defect has formed in the coating, thus the substrate has to be exposed to a partially corrosive environment, the zinc-rich primer layer plays its role in providing protective protection to delay the onset of electrochemical reaction (corrosion) of the substrate. The amount of sacrificial protection provided depends on variables such as the purity of the zinc dust used, the presence of moisture and the electrical conductivity between the substrate and the interconnected zinc particles. Thus, the zinc used in the primer is anodic to the ferrous substrate which acts as the cathode. When zinc particles are converted to zinc oxide, the yajna protection ends.

In his paper "Epoxy Zinc Rich Primer Coating", Peter concludes that in general "inorganic zinc coatings may provide better rust protection than organic zinc coatings." Rust protection provided by coating systems with zinc-rich primers was found to be superior to protection provided by organic coatings without zinc-rich primers.
Performance of Epoxy Zinc Rich Primer Coating
Compared to zinc-rich silicates, the major advantages of zinc-rich epoxies include:
Ability to heal faster regardless of ambient humidity.
Overcoating facility.
Ability to increase the thickness of the film without the risk of cracking the soil.
Suitable for using standard airless sprays, without using special equipment for zinc-containing sprays. Silicate
High tolerance for variable surface conditions and low hardness surface quality requirements for substrates. For example, impermeable surfaces can be protected by an epoxy primer containing zinc to clean abrasive blasts.

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