Problem Solving Forum
June 5 - June 9, 2017
What would be a reasonable service life for a two-coat, zinc-rich epoxy/epoxy mastic system, about 200-250 microns, in a marine environment? What evidence is there from the field?
Larry Muzia of Exceletech Coating & Applications, LLC on
June 13, 2017:
I no longer have a copy of the Gordon Brevoort stu ...read more I no longer have a copy of the Gordon Brevoort study on coating life expectancy in various environments; however, experience allows me to interject the following. First off, I will assume this is carbon structural steel, so the first order of business is what type of surface preparation did the steel receive before the application of the organic zinc. It will have an effect on service life. Assuming an SP 10 prep followed by removal of non-visible contaminants followed by sufficient film thickness of a highly loaded zinc-epoxy, this system will be a reasonably good primer choice in a marine environment. The question I have about the epoxy mastic is, does i,t have aluminum platelets within the composition. As typical epoxy mastic is noted for lower film stress which can equate to permeability rating. The mastics with platelets have the ability to impede the passage of the water molecule (electrolyte) and can enhance the performance. The other consideration is where specifically is the marine environment? Colder climates also have lower corrosion rates than for example the Space Coast here in Florida. My opinion is on average this system would perform 8-12 years with proper maintenance in your average atmospheric marine environment .
Regina Montgomery of Thordon Bearings Inc. on
June 13, 2017:
I would be interested in hearing experiences for c ...read more I would be interested in hearing experiences for coatings of this thickness. My experience is with 160-280 micron, two-part epoxy coatings designed to provide up to 15 years performance integrity for protecting marine propeller shafts. Service life is, however, based on typical conditions and can't take into account extreme conditions such as damage caused by ropes, groundings, or flotsam. Other difficulties include stray currents or marine growth where anti-fouling protection falters, which cause coatings to be compromised.