It’s Time to Rethink Zinc



Ceramic epoxy technology has become a staple for the care of water and wastewater assets throughout the United States. Treatment plants, distribution pipelines and storage tanks have all benefited from thick-film ceramic epoxy linings, which can be applied direct-to-metal; however, they are often paired with zinc-rich primers in the field and in shop environments. With the introduction of Ceramaprime, a new thin-film ceramic epoxy primer from Induron, asset owners, contractors and specifying engineers are invited to "rethink zinc" as their go-to priming option.

Zinc-rich, moisture-cured urethane primers have dominated the water industry during the past 20 years. The primary salable attribute of these primers has been the promise of longer service life due to the addition of a "sacrificial layer" of coating in the form of a zinc-rich primer. While these primers continue to perform admirably, the real reason they have gained purchasing support from the contractor community lies in their user-friendly application properties. Zinc-rich primers dry quickly, are applied in a thin film and offer an extended recoat window — all attributes that have been difficult for epoxy technology to match.

Throughout the reign of zinc-rich primers, however, many owners have stayed with epoxy primers out of a safety concern about using heavy-metal-containing products on projects that involve drinking water — and they're paying nearly double the price per gallon to do so. When comparing evaluations of assets coated with zinc-rich primers versus epoxy primers, there is a lack of noticeable difference in performance.

If the top coats applied to either primer are performing well, then properly applied primer need only guard against one mechanism of failure: undercutting corrosion where breaks in the film occur. While zinc-rich primers are billed as well-suited for this protection due to their sacrificial nature, the value of this particular attribute should be more carefully considered. Would a layer of disappearing, sacrificial primer truly retard undercutting corrosion? If the corrosion cell remains active, does changing the source of its electrons to the coating itself help the coating system stay intact?

Induron asserts that ceramic epoxy has always offered the best defense against undercutting corrosion. The addition of precisely engineered blends of ceramic beads to the epoxy results in a film that has greater adhesion to the substrate than cohesion to itself. By contrast, traditional epoxies with film cohesion greater than substrate adhesion will undercut and expose additional substrate. Tipping this scale stops undercutting corrosion in its tracks. While this performance advantage has been understood for decades, ceramic epoxy has never been used as an alternative to zinc in the production of a thin-film primer — until the recent introduction of Induron's Ceramaprime.

With Ceramaprime, Induron has distilled the performance of thick-film ceramic epoxy liners into a thin-film primer. The new product boasts a 45-minute time-to-recoat, a one-year maximum recoat window and low moisture vapor permeability. This NSF-approved product mitigates undercutting corrosion, offers over four hours of pot life, cures hard enough for fabricators to stack steel plate in only seven hours and can be easily applied with standard airless spray equipment to both atmospheric and immersion exposure substrates. Ceramaprime also eliminates exposure to reactive metals and isocyanates.

Induron is currently working with specifying engineers to update their specifications to ceramic epoxy primer. As new epoxy technology like Ceramaprime continues to evolve, many more asset owners, contractors, OEMs and specifying engineers are sure to rethink zinc to help cut costs and control corrosion.

*Claims or positions expressed by sponsoring authors do not necessarily reflect the views of TPC, PaintSquare or its editors.