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September 21 - September 25, 2020

What causes bubbling or cratering of epoxy intermediate coat when applied over epoxy zinc-rich primer?

Selected Answers

From Wole Abimbola of Navante Oil and Gas Company Limited on September 25, 2020:
Insufficient overcoating time of the zinc-rich primer will cause remnant solvents to force their ways out through the epoxy intermediate, thereby causing craters and bubble appearances.

From Marco Fabio Ramenzoni of ZINGA METALL BRASIL on September 22, 2020:
True Zinc Rich Primers are porous, after applied. The higher the Zinc content, more porous it will be. When a sealant or other layer is applied over a Zinc Rich primer, it will “try” to fill up the spaces of this porosity expelling the air contained in those spaces towards the surface. If the dynamics of the sealant layer is not to let the bubbles out quickly, the result is that these bubbles will end up entrapped forming surface bubbles or, later, craters. Therefore, to avoid this problem, it is important to apply the following layer to a Zinc Rich Primer using the “mist coat – full coat” technique, witch consists of applying a very thin layer first, letting the air from the porosity to escape forming bubbles that will collapse and close the film, and only then applying the full coat according to specs.

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Tagged categories: Asia Pacific; EMEA (Europe, Middle East and Africa); Epoxy; Latin America; Maintenance + Renovation; North America

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