The Effect of Feathering on Coating Performance

From JPCL, June 2019

By Patrick Cassidy and Michael Kibler, Elzly Technology Corporation; and Cameron Miller, Paul Slebodnick and James Martin, U.S. Naval Research Laboratory

Feedback from waterfront personnel performing maintenance painting for the U.S. Navy has consistently questioned the Navy’s requirement for performing feathering. NAVSEA Standard Item (NSI) 009-32 defines feathering as tapering the edges of tightly adhering old paint at an approximate 30-degree angle into the newly prepared bare metal surface. This article describes a U.S. Naval Research Laboratory program designed to test the hypothesis that feathering does not affect repair coating system performance and discusses what this testing revealed....

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Tagged categories: Feathering; Patrick Cassidy; Performance testing; Surface Preparation; U.S. Navy

Comment from Stuart Ross, (6/14/2019, 11:50 AM)

The human error factor plays the most significant role in weather or not a coating/repair fails prematurely or performs according to it's life expectancy. Not including an abrasive blast repair, feathering a repaired area 'should' ensure that no future corrosion cells are hiding under the (irregular) edges of a coating. Conversely, will a hot, tired, or lazy worker physically check 100% of the exposed coating edges of a repair with a dull putty knife to confirm tight adherence, if it is not visibly lifting? Doubtful. While I respect the findings of the laboratory tests under controlled conditions, Imho, feathering in this case is more of a visual sign that all exposed edges have been addressed and no visible moisture or other agent has entered into or under the existing coating system unnoticed.

Comment from Patrick Cassidy, (6/17/2019, 10:00 AM)

Stuart, great comments. I agree with you that human factors play a huge role in this and every other coating and surface prep process. What we saw in our testing was that feathering did not provide any more guarantee that the edge was ready for coating application than not feathering (i.e., there was just as much coating failure at the edge, and lifting coating, when feathering as when not feathering). Performing touch-up painting is difficult and time consuming. In our experience the feathering step did not seem to be a visual sign that all exposed edges had been addressed, as coatings still failed when feathering was performed. Feathering should not be used as a QA/QC step. The worker should be in the habit of using the primary prep method or tool to ensure they reach sound intact tightly adherent coating per the SSPC SP standard. Finally, while half of this testing was conducted in the lab, the other half was done in the field using real shipyard workers under real conditions on a mock ballast tank, and a third study (not included here, but can be found in our SSPC 2019 Conference Paper) was done on ship using shipboard maintainers. So two thirds of the results are "real world" results, not controlled lab conditions. Thanks again for the comments.

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