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Question posted - January 26 to January 30, 2015:

What are the pros and cons of using an organic vs. inorganic zinc primer?


Selected Answers

From Ahren Olson of Covestro on January 5, 2016:
 The pros of using IOZ over OZ include excellent galvanic protection, slightly better than OZ. IOZ can also be used untopcoated in the correct environmental conditions.  IOZ has significantly higher heat resistance than OZ. The  cons of using IOZ over OZ are, first,  that IOZ requires humidity (moisture) to cure, typically above 50% relative humidity, which can be very problematic in the winter months for most shops; and also that IOZ typically require a higher level of surface cleanliness (SSPC-SP 10 or greater). Additionally, IOZ tends to mudcrack when applied too thick, while OZ tend to be more tolerant of excessive film thickness.  IOZ also requires a mist coat if  it is going to be topcoated to prevent outgassing.

From Todd Williams of Covestro on January 5, 2016:
There are several circumstances where inorganic zinc is a fitting choice over organic zinc for atmospheric service conditions. These include shop-applied coatings where zinc-rich primers are exposed to UV before applying the final coats and high temperature applications. In all other scenarios, the possibility exists to use either organic or inorganic zinc and additional considerations must be taken into account. Oftentimes, inorganic zinc systems are specified because of slightly improved corrosion resistance obtained when applied under ideal conditions versus organic zinc. The ideal conditions can be very different from a project’s actual application conditions. Several recent papers have highlighted that prudent coating selection should be based on systems that have the best chance for success in real world conditions, not   strictly upon the coatings performance. For example, inorganic zinc coatings require extremely clean surfaces (Sa 2½+) and humidity to cure, and if humidity is not present directly after application, the coating may not ever cure properly even upon re-exposure to moisture. Unless humidity can be controlled during dry application conditions, the results can be disastrous – the production schedule will be significantly slower than expected or curing will be insufficient, leading to cohesive coating failures in the field. Furthermore, application issues of inorganic zinc such as mud cracking, dry spray, specialized application equipment and topcoat pinholing are not issues when using organic zincs. Since application errors are responsible for the majority of all failures, the performance benefits gained using inorganic zinc must be weighed against potential application errors, especially when inexperienced applicators are involved.

From Usama Jacir of Cortec Middle East on May 31, 2015:
My understanding is you will get a higher utilization of the zinc galvanic properties due to the conductive nature of the inorganic binder, therefore better protection. A consideration in dry environments is the inorganic zinc require moisture for curing, making it harder to apply. In some of our regions, we have to actually force cure it by spraying with water.

From Paiboonsak Saengsomboon of JT Marketing Co., Ltd. on March 13, 2015:
They are both very good at corrosion protection. They both provide a cathodic effect to steel surfaces. The difference between the two types are, first, that inorganic zinc performs in higher service temperatures (up to 400 C), while organic or epoxy zinc performs only up to 120 C; and second, that inorganic zinc can be used alone at specified thicknesses, e.g., as a tank coating for some kind of chemicals, but organic zinc needs to have a topcoat.  Neither of them is good as a primer for underwater areas due to high porosity and osmotic blistering.

From Larry Muzia of Exceletech LLC on January 28, 2015:
Inorganic zincs (IOZs) offer a high level of galvanic protection as there is direct zinc to metal contact. In an organic zinc (OZ) the metal is bound in an organic resin and does not provide the same level of galvanic protection. OZs are easier to overcoat as they do not outgas, which may occur with an IOZ. IOZs can provide a high level of corrosion protection untopcoated, provided the environmental pH is within 5-10. IOZs require rigorous surface preparation and close adherence to dry film thickness specifications. They also require a minimum of 50% humidity to properly cure by hydration. Like any primer types,  no single zinc rich type is best for all conditions.


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Tagged categories: Primers; Zinc-rich (inorganic); Zinc-rich (organic)


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