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July 13 - July 17, 2020

Why are zinc-rich paints generally not used for an immersion environment, despite the superior anti-corrosive protection?

Selected Answers

From Peter Bock of Performance Polymers Americas LLC on July 16, 2020:
Over the decades, both the formulation and definition of "Inorganic Zinc" have changed. In the 1960's and 70's, when post-cured inorganic zincs were widely specified and used, those formulations were a standard one-coat system for tank linings where the stored product was water, and they performed well. Those products became unavailable in the 1980's, and today's ethyl silicate IOZ formulations do not hold up well in water immersion service.

From Mark Edmonds of Placer Inspection on July 15, 2020:
Earl is correct about one Waterborne High Ratio Inorganic Zinc single coat system successfully being used in immersion. He and I worked on a project for many years applying that product to literage pontoons for the US Navy (NAVFAC). It works very well.

From Earl Ramlow of Polyset on July 14, 2020:
The key word for the main reason(s) zinc-rich coatings have not been used in immersion is actually in the title of the forum question. The industry, for some time, has “generally” considered zinc-rich coatings, specifically inorganic zinc (IOZ) rich coatings, the same technologies and performance results. Grouping all “IOZ” products into a “general” category is inaccurate and has caused people to think of them as the same in many respects. However, there are many different chemistries that effect performance in every application setting. There are solvent-borne, solvent-based, water-borne, water-based, standard ratio, high ratio, sodium, lithium, and potassium silicates; all very different IOZ products and they are NOT the same. There is one Waterborne High Ratio Zinc Silicate (inorganic) Single Coat System that has years of excellent corrosion prevention in immersion settings in both freshwater and saltwater applications in the Energy (Hydro) industry, DoD and, Offshore industries. This coating system provides long-term corrosion prevention and is found to be in the same condition today as it was when first installed – regardless of the length of time – and will continue to provide superior corrosion prevention for many years to come. As with anything, if you put the wrong product technology in the wrong application setting and treat a wide variety of “IOZ” products “generally” as a common technology or “all things being equal," there will be failures and continued lack of use.

From Jaime Marcos of Profesional independiente on July 14, 2020:
In immersion service, the paint layer applied on the zinc-rich paint to peel off. Zinc produces zinc salts, which are hydrophilic. The paints are permeable, over time. When reacting with the salts, they swell (increase their volume), causing the layer to detach.

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Tagged categories: Asia Pacific; Coating Materials; EMEA (Europe, Middle East and Africa); Latin America; North America; Zinc-rich (inorganic); Zinc-rich (organic)

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