Differences between epoxy zinc-rich paint and inorganic zinc-rich paint

Since they are both zinc-rich primers, many users have various doubts regarding the choice between inorganic zinc-rich primers and epoxy zinc-rich primers. Which paint is the best to use? In the corrosion protection systems for steel structures using multi-coating systems, epoxy zinc-rich coatings and inorganic zinc-rich coatings have similar performance, so epoxy zinc-rich primers can be used in place of inorganic zinc-rich primers. From the perspective of construction and construction speed, epoxy zinc-rich primer is more suitable. Recently, many large-scale steel structure projects in China have begun to make extensive use of epoxy zinc-rich primers, such as the main stadium for the 2008 Olympics (Dalian Zhenbang Paints), the expansion of Beijing Airport (International and Haihong Paints), the expansion of Shanghai Pudong International Airport (Shanghai Kailin Paints), and the Chaotianmen Yangtze River Bridge in Chongqing (Zhou Dun Paints). The main stadium for the 2000 Sydney Olympics (International Paint), the 2004 Athens Olympics (International Paint), and so on, all used epoxy zinc-rich primers. Inorganic zinc-rich paint outperforms epoxy zinc-rich paint in terms of heat resistance, solvent and chemical resistance, as well as electrostatic discharge properties, but it has poorer film flexibility and application characteristics. Inorganic zinc-rich paint has some special requirements during application; for example, its curing depends on a high relative humidity, and the porosity of its surface necessitates the use of mist spraying techniques. In contrast, the application requirements for epoxy zinc-rich paint are much simpler. The advantages and disadvantages of epoxy zinc-rich primers and inorganic zinc-rich primers in terms of application are shown in the table below:

| Comparison Item | Epoxy Zinc-Rich Primer | Inorganic Zinc-Rich Primer |
|------------------|------------------------|--------------------------|
| Curing Environment | Suitable in environments with relatively low humidity; no impact on the curing reaction. Does not cure at low humidity; even if it appears dry, watering is required to accelerate the curing process. | – |
| Mixing Requirements | Easy to apply; no need for continuous mixing. If mixing stops, zinc powder will settle. | Requires continuous mixing; otherwise, zinc powder will settle. |
| Repainting Ability | Easy to repaint; no need for a sealant. However, the porous surface can cause pinholes and bubbles in subsequent coats, requiring special spraying techniques such as mist spraying. | Repainting is possible, but the porous surface can lead to defects in subsequent coats. Special spraying techniques are needed. |
| Repainting Interval (at 23°C) | 1.5 hours | Longer interval; curing tests (using MEK) are required before applying subsequent coats. |
| Repairability | Damaged areas can be easily repaired. It is designated by the American SSPC for repairing inorganic zinc-rich primers. Sensitive to poor surface preparation; damaged areas tend to delaminate. | Difficult to repair; damaged areas easily delaminate. |
| Coating Flexibility | The coating is less brittle and more flexible compared to inorganic zinc-rich primers. | The coating is brittle and lacks flexibility. |
| Thickness Control | If the thickness exceeds 125/150 microns, cracking of the coating may occur. | – |

In summary, inorganic zinc-rich primers require curing in the presence of moisture, have long intervals between repaints at normal temperatures, necessitate curing tests before applying subsequent coats, and require special spraying techniques ； For epoxy zinc-rich primers, it only takes 1.5 hours to apply the intermediate coat; with conventional construction methods, this results in high efficiency and can **reduce tight construction schedules**.

These days, few people use zinc-rich paint without an organic component; epoxy zinc-rich paint is generally used instead.

Additional information on the second floor: First, inorganic zinc-rich primers – since the inorganic silicate binder reacts not only with zinc powder but also with the base metal iron – form a chemical bond; as a result, their corrosion resistance and durability are superior to those of epoxy zinc-rich primers. Correspondingly, the requirements for surface treatment for these primers are also higher than those for epoxy zinc-rich primers. Inorganic zinc-rich surface treatments have higher requirements; sandblasting for rust removal is needed to reach Sa2 1/2 grade, whereas for epoxy zinc-rich coatings, Sa2 grade is sufficient. Second, the heat resistance, solvent resistance, and electrical conductivity of inorganic zinc-rich coatings are superior to those of epoxy-based coatings, but their mechanical properties are inferior to the latter. III. Epoxy zinc-rich primers are easier to pair with topcoats ； Inorganic zinc-rich primers are subject to certain limitations: for example, their surfaces have many pores, which can cause bubbling when a topcoat is applied; moreover, there are requirements regarding the alkali resistance of the topcoat, and the primer itself must be fully cured before the topcoat can be applied, otherwise adhesion will be poor and peeling is likely to occur. IV. The epoxy zinc-rich primer improves the performance of inorganic zinc-rich primers in terms of application, and is less affected by environmental factors. Inorganic zinc-rich coatings offer better rust prevention performance, but they require higher standards for surface treatment ； Epoxy zinc-rich coatings have better physical and mechanical properties, and require fewer requirements regarding surface treatment. V. The inorganic zinc-rich primer is a water-based paint and is weldable; the epoxy zinc-rich primer is a two-component solvent-based liquid epoxy coating.

The inorganic zinc-rich primer is a water-based coating; as the name suggests, it uses pure water as a diluent, and it can withstand temperatures up to 400 degrees； Epoxy zinc-rich primer is a solvent-based coating that requires dilution with a thinner.

We use epoxy zinc-rich paint for wind turbine hubs; it is easy to apply and yields good results.

What was said on the third floor is really great! The heat resistance, solvent resistance, and electrical conductivity of inorganic zinc-rich coatings are superior to those of epoxy coatings, whereas their mechanical properties are inferior. If the surface treatment is of good quality, inorganic zinc-rich coatings are superior to epoxy zinc-rich coatings

Inorganic zinc-rich primers aren’t very widespread, are they? Except where large marine equipment is required.

Inorganic zinc powder requires high standards for the surface treatment of equipment. In the case of epoxy coatings, they are not sensitive to the thickness of the paint layer, but this is not the case with inorganic zinc powder; once the thickness exceeds a certain level, the paint will peel off. Therefore, choosing the right thickness is very important, and paint suppliers usually provide recommendations regarding the appropriate thickness. Also, inorganic zinc powder does not necessarily have as good resistance to rain and moisture as epoxy; it is a water-soluble paint.

Comparison between epoxy zinc-rich primers and inorganic zinc-rich primers