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April 14 - April 18, 2014

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?

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Selected Answers

From David Lemke of Team Industries on April 29, 2014:
We have applied the 3-coat systems using both OZ and IOZ primers in a shop atmosphere. The problem with the IOZ is the moisture cure of the product. In a heated shop in winter, where I live, the heat just sucks out the moisture, making the coating tough to cure out. We have a special room where we induce moisture to cure the IOZ. Then there is the added mist coat that normally doesn’t need to be done on the OZ. The OZ dries much faster and is a preference on 3-coat systems. If Will is right about the performance of both a primers in 3-coat systems, I wish some of our customers knew those results. It would make my life easier.

From Samuel Felisario of PT RAJAWALI HIYOTO on April 29, 2014:
I agree with David Lemke: in terms of performance, IOZ is better. However, OZ is more user-friendly.

From Will Fultz of Sika Greenstreak / Tuff-N-Nuff on April 28, 2014:
The short answer is that there are few differences in performance for OZ and IOZ primers when they are used within three coats systems. Look at the weathering test results generated by numerous state DOT authorities, and you will come to this conclusion.

From Willie Mandeno of Opus International Consultants Ltd. on April 28, 2014:
There are no significant differences when correctly applied, then topcoated with organic intermediate/finish coats and exposed to normal atmospheric conditions. Zinc silicate's significant difference is its superior performance under atmospheric exposure when applied without a topcoat due to its more durable and conductive binder, which is more resistant than organic zinc-rich coatings to UV, heat, and abrasion.

From David Lemke of Team Industries on April 25, 2014:
Inorganic (ethyl silicate) zincs will have more zinc attached to the immediate surface of the substrate to offer cathodic protection, while organic (epoxy zinc-rich) zincs will have the zinc suspended throughout the film layer for that cathodic protection. Therefore, the inorganic zinc will offer more cathodic protection than the organic because more zinc will be on the surface of the substrate. The organic can offer the cathodic protection as an electrolyte permeates through the film if that happens. As Dan mentioned, inorganic zincs can withstand higher temperature service environments and UV protection over the organic zincs. Some coating manufacturers will allow a SP-6 surface cleanliness standard for the application of inorganic zincs but will state that in severe service environments a minimum of SP-10 surface preparation will be required. Organic zincs can be usually applied to a lesser degree of surface preparation. So to me the significant differences are that inorganic zincs will offer more cathodic protection, UV resistance, and withstand much higher service temperatures. Organic zincs can be used in situations where elevated surface preparation is not attainable as long as heat is not a factor. Most organic zincs can have a coat of urethane applied over the top for UV protection because heat is not a factor.

From Louis Vincent of L.D. "LOU" VINCENT PHD LLC on April 24, 2014:
Inorganic zinc primers have the longest proven corrosion prevention, whereas the organic zinc-rich primers have the most user-friendly application. The real problem lies in applicator training. Most applicators are trained on organic coatings, mostly organic topcoats. When faced with applying an inorganic primer, they use improper techniques because they were never trained on inorganic zinc primers. Mud-cracking is an applicator problem, not a coatings problem.

From Derek Righinni of Certified Coating Inspection Ltd on April 24, 2014:
Brian, both ethyl silicate and epoxy zinc-rich coatings may provide cathodic protection if loaded with sufficient zinc pigment so that the pigments are in contact. Ethyl silicate is prone to mud-cracking, but this is an application difference and not a performance difference. Dan, again you are focusing on application differences. Organic binders are subject to the same frailties as all organic beings, including extremes of temperature, aging, and UV; whereas, inorganic binders are far more resistant to our organic frailties and perform much better when exposed to UV, extremes of temperature and time.

From Brian Chapman of Cadillac Fabrication on April 23, 2014:
I believe, in the simplest terms, that one offers cathodic protection while the other is a barrier coat.

From Neelakandan S of Carboline RPMSaudiArabiaLLC on April 19, 2014:
I agree with Dan Durus, who mentioned valuable points. Also, notable  differences favoring epoxy zinc-rich include hardness,  excellent bond strength, and greater adhesion, when compared with inorganic zinc-rich counterparts, which are known for mud- cracking and poor scratch hardness resistance.

From Jim Boyce of Insl-x Products Corp on April 18, 2014:
The direct zinc-to-substrate contact is greater with the zinc-rich ethyl silicate.

From Dan Durus of Chimtitan on April 15, 2014:
The drying time for ethyl silicate zinc-rich primer is much less than for epoxies. The temperature resistance for ethyl silicate is up to 400 degrees C and can be up to 600 C if it is topcoated with aluminum silicone. Also a zinc-rich ethyl silicate primer requires a minimum surface preparation of Sa 2 1/2 (SSPC-SP 10).

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

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