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Bridge Coating Performance: Two-Coat vs. Three-Coat Systems

From JPCL, May 2014

More items for Coating Materials

by Shameem A. Khan, Maryland State Highway Administration

The author describes the results of various performance tests to determine whether two-coat or three-coat coating systems would provide the best protection for bridge rehabilitation at the lowest cost. The article also breaks down the evaluation process step-by-step and explains the significance of each of the testing criteria....
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Tagged categories: Bridges; Coating chemistry; Coatings systems; Coatings technology; Corrosion protection; Performance testing; Site/field testing

Comment from Gregory Berg, (6/9/2014, 8:06 AM)

Very impformative test. Only thing I would have liked to have seen would have been a zinc rich epoxy with two high build coats of acrylic.

Comment from Doug Wolthausen, (6/9/2014, 6:22 PM)

Another system to test is an Organic Zinc and Polysiloxane

Comment from Tom Schwerdt, (6/10/2014, 10:11 AM)

Doug - there are dozens of potential system types, each generally available from many different manufacturers.

Comment from Mark Puckett, (6/10/2014, 3:24 PM)

why didnt they report the coating manufacturers and products??

Comment from Pamela Simmons, (6/12/2014, 4:40 PM)

Mark, we forwarded your question to the author. His response: “When we advertise we place a generic description of the paint system required and do not indicate any system by name. For your information we may provide a copy of the generic specification that we are using on all jobs.”

Comment from Brian D. Madsen, (6/16/2014, 4:36 AM)

Is the right term “cohesion failure”, when the failure is between two coats ? Shouldn't it be “adhesion failure” ? ( system K).

Comment from David King, (6/16/2014, 10:24 PM)

I note both systems show peeling and would ask what the RH was during and for what period after application. What percentage of the visible rust staining with the elastomeric, was rust bleed?

Comment from Tom Schwerdt, (6/17/2014, 8:21 AM)

Cohesion failure: When a coating film splits internally within the film (layer). Adhesion failure: When a coating film debonds from a substrate (which can be a lower layer of paint.)

Comment from Pamela Simmons, (6/17/2014, 10:20 AM)

The author was contacted for clarification. His response: “Coating System K showed areas of rust, peeling, adhesion and cohesion failure between the primer and finish coat, and finish coat itself on approximately 10 percent of the total surface area.” The online version of this article will be corrected accordingly. Please feel free to contact Mr. Khan directly at

Comment from Chris McEvoy, (6/18/2014, 10:30 AM)

It would be interesting to show test results from a system of 10.0 - 12.0 mils DFT Epoxy Mastic plus 2.0 - 4.0 mils DFT Polyurethane.

Comment from Nathan Spencer, (6/18/2014, 7:47 PM)

That is really poor performance. I suspect there are some prep/application issues. I have seen better performance out of one coat aspartic polyurea, or even aromatic polyurea for that matter.

Comment from Eric Kline, (6/30/2014, 8:46 AM)

Nice work! The issue of advances in the possible uses of two and perhaps even one coat systems can still use further research. As was said by Edison, "...

Comment from Eric Kline, (6/30/2014, 8:51 AM)

Actually, it was said by Michael Faraday, ..."but still try, for who knows what is possible?"

Comment from Will Fultz, (7/17/2014, 9:36 AM)

I would be curious to see how a system which is nothing more than one coat of an IOZ primer at 3.0 to 4.0 mils would perform.

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