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November 25 - November 29, 2019

Does roller nap decrease the lifespan of a three-coat OZEU (organic zinc prime coat, an epoxy intermediate coat and a urethane finish coat) paint system? Is there a visual guide or specification for this in the industry or test results available for study?

Selected Answers

From Luc N. Turenne of Western Industrial Services Ltd. on December 18, 2019:
Decreased performance must be accepted if spray application is not permitted or is not practical, as is the case in many facilities. Alternately, a different primer should be explored.

From Aajjay Sunkay of ASSETREIFURB ENGINEERRS on November 27, 2019:
The objective in using an OZEU system is to protect the metal surface. The primer layer of organic zinc-based coating protects by sacrificial means, followed by epoxy coating as intermediate coat and urethane as top coat . Zinc particles blended blended with the organic, liquid resin  are most important and act as a sacrificial anode and form an oxide layer to protect further. The  intermediate coat and top coat protect the surface by their barrier properties. Hence, the life span of this coating system is assured by the cumulative effect of all these inherent characteristics of the different coats. When we use a roller nap for application of the zinc-based organic coating, zinc particle get trapped in the roller and only liquid will lie on the metal surface, which results in an uneven quantum of zinc particles on the surface, which will  hamper the basic objective of sacrificial anode formation and weaken the oxide film formation,  keeping open sites in the film for liquid to reach to metal surface. Hence, application of an OZEU coating system with a roller nap reduces the life span of coating.  It  needs to be applied by spray with thorough stirring of the paint before application.

From Erik Andreassen of CPS on November 25, 2019:
A roller should never be used for application of a zinc coating. For people in our trade, the reasons are obviously known: air inclusions, lack of wet film application, only liquid applied instead of zinc. Other coats can be applied but not recommended if you require a high build system.

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Tagged categories: Brushes and rollers; Coating Application; Paint application

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