1. Steven Easton
Owner/Chief Quality Officer at EQM Services (Canada)
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Wet Storage Stain and Your Mechanical Components
March 10, 2016
If you have galvanized steel components in your facility, you might notice that some of these
components are covered with a white, powdery residue on the surface of the zinc coating. This
residue is caused by moisture reacting with the zinc coating on the metal, causing a chemical
reaction and corrosion of the protective zinc layer.
How does this happen?
Zinc is a reactive metal, but corrodes very slowly because it develops a continuous passive layer
on the surface. This passive layer develops best when the zinc is allowed to remain dry. Normal
weather conditions have little impact on the development of this passive layer, however, if the
zinc coating is kept in a wet, unventilated area, then the reaction between the water and zinc
coating causes zinc hydroxide (ZnOH) to form, allowing corrosion and eventual loss of the
coating and exposure of the parent metal to the environment.

2. Wet storage stain, or white rust, often occurs as a result of poor storage and drying at the
galvanizing facility, but can also develop or be exacerbated on construction sites with poor
material handling practices. Components that are tightly bundled after galvanizing are not given
adequate opportunity to dry, creating conditions for wet storage stain. Similarly, galvanized
components that are received onto your construction site, then placed in wet storage conditions
(direct contact with mud, grass, etc.) can develop white rust.
How Serious is White Rust?
Light layers of white rust will eventually be converted to zinc carbonate during normal conditions
and posses no risk to the protection of the underlying metal. Moderate to severe levels may
require treatment or, if severe, replacement of the affected component. While white rust may not
look pretty on your component, it is often just a cosmetic issue. If your customer has specified a
galvanizing standard (ASTM A123, ASTM A653) for steel used in your components; coating
condition, thickness and repair may require special procedures to ensure service life of galvanized
materials.
Storage with insufficient ventilation
between components. Susceptibility
to white rust.
Example of moderate levels of wet
storage stain. Repair or replace per
customers specifications.
Example of severe wet storage stain.
Regalvanizing required.
Quality assurance plays a key factor in ensuring the fitness of your galvanized product. Paying
attention to your suppliers storage and handling practices, your project receiving and storage
procedures and your storage of materials during production can reduce or eliminate costly repairs
and replacements of galvanized materials. For more information on how EQM Services can
support your supplier or project quality requirements, please contact us at info@eqmservices.com