Small volumes of water occasionally

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Zinc oxide and zinc hydroxide do not provide a durable corrosion-resistant coating; the hydroxide must next react with atmospheric gases to form a continuous layer of passive and strongly adherent zinc hydroxy-carbonates. For this to occur, zinc surfaces need to go through many cycles of wetting and drying.

Corrosion on concealed galvanized steel supports for marble bathtub. Photo courtesy Building Diagnostics Asia Pacific
Corrosion on concealed galvanized steel supports for marble bathtub. Photo courtesy Building Diagnostics Asia Pacific

If galvanized steel remains in prolonged contact with concealed films rcs data of water lacking dissolved oxygen and carbon dioxide, the sequence of reactions ultimately producing stable zinc hydroxyl-carbonates may stall. Conversion of zinc to powdery oxide and porous encrustations of hydroxide can continue unabated until moisture penetrates the zinc layer and instigates corrosion of underlying steel.

In refurbishing guest suites of a five-star hotel in Hong Kong, for example, interior designers elected to enclose cast iron bathtubs with polished white marble. In less than two years, marble benches in numerous suites displayed vivid orange stains. Investigation confirmed the source of the rust stains was corrosion of hot-dipped galvanized steel plates and angles supporting the marble on an intermediate layer of conventional polymer-modified tile adhesive.