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May 22 - May 26, 2017

What are the significant performance differences between an inorganic zinc primer (ethyl silicate) and an organic zinc primer (epoxy), given the same application and exposure conditions?

Selected Answers

From trevor neale of TF Warren Group on October 19, 2017:
Great summary Larry ! Another factor in selecting inorganic zinc over organic is the open recoat window when projects are anticipating very long delays (12+ months) between priming and final paintin., Of course, that does not preclude the need for the correct surface preparation when coating does eventually take place.

From jiyash bhaskaran of Samsung engg on October 18, 2017:
In my experience, the main difference between IOZS and zinc rich epoxy is in the application. IOZS application needs more care and precautions during application, such as 1) continuous agitation of paint during application; 2) more controlled application techniques including number of passes and tip sizes because excessively thick DFT may lead to mud cracking; 3) avoidance of dry spray by adjusting gun distance and application temperature; 4) MEK test for curing check; 5) mist coat technique for top coating to avoid pin holes; 6) water sprinkling for curing if RH is less than 50%. But for zinc rich epoxy, we can apply like any organic coating.

From Larry Muzia of Exceletech Coating & Applications, LLC on May 23, 2017:
First off is the type of protection: inorganic zinc is a sacrificial coating and the organic zinc is a blend of sacrificial and barrier protection. An inorganic zinc will offer much higher temperature resistance and in the right environment can be a stand-alone protective system, whereas organic zincs should be top-coated for long-term performance. The inorganic zinc is very porous; however, because the zinc acts as the anode, the resulting zinc carbonate salts fill the open porosity and act as an inorganic barrier not broken down by UV and acting as a quasi-topcoat,thereby reducing the rate of sacrifice of the zinc.  Other than the temperature-resistance difference,inorganic zincs will offer better resistance to salt-laden atmospheres; however, they will break down rapidly in an environment with a low ( less than 5) or high ( greater than 10) pH. Inorganic zincs also do a better job of protecting bare or damaged areas of the steel due to the throwing power of the anode. In an organic zinc film the zinc tends to be encapsulated within the binder. Albeit not necessarily a performance issue, but the organic zincs are easier to topcoat as pinholing is not normally an issue as can sometimes be the case with an inorganic zinc, if proper procedures are not exactly followed. Inorganic zincs are also less tolerant of excessive film build and surface profile issues, whereas organic zincs will be more forgiving on less than a properly prepared substrate. I have often used the  phrase,   "inorganic zincs tend to be self-inspecting" because if improperly prepared and applied, they tend  in most cases to demonstrate some form of  "something is wrong here" very soon.

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Tagged categories: Coating Materials; Epoxy; Zinc-rich (inorganic); Zinc-rich (organic)

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