1.What is white rust?
White rust is the initial product of corrosion of the galvanized layer in a humid, poorly ventilated environment. Its main components are basic zinc carbonate and zinc hydroxide. It can be understood as a "skin disease" of zinc; it is proof that zinc is sacrificing itself to protect the steel base, but it also means that the outermost layer of zinc has been consumed.
2.What are the effects of slight white rust (a small amount of white or gray powder on the surface, without blemishes)?
Impact: Very small, almost negligible.
Cause: This white rust only occurs on the outermost zinc layer. After cleaning off the powder, a large area of intact zinc layer remains underneath. The corrosion resistance of galvanized coils depends primarily on the thickness of the remaining zinc layer; the negligible loss of the surface layer has little impact on the overall "sacrificial anode" protection.
Cleaning Method: Simply wipe with a clean, soft cloth, a soft brush, or a dedicated nylon brush.
3.What are the effects of moderate white rust?
Impact Level: Some impact; it will shorten the lifespan of the corrosion protection layer.
Cause: White rust has penetrated deep into the zinc layer, forming localized corrosion spots. After cleaning away the corrosion products, the zinc layer in these areas will become thinner, potentially even exposing the zinc-iron alloy layer. Although the overall protection remains intact, these thinned spots will become weak points that are preferentially corroded in the future.
Cleaning Method: More thorough cleaning is required, such as using a stiff-bristled brush or scouring pad. After cleaning, it is recommended to check the surface for any significant loss of thickness.
4.What are the effects of severe white rust (a large amount of white deposits on the surface, with red or brown rust appearing)?
Severity of impact: Severely impactful, with a significant decrease in corrosion resistance.
Cause: This indicates that the white rust has completely corroded away the pure zinc layer on the surface and has even penetrated the zinc-iron alloy layer; the steel substrate may have begun to rust (red rust). Cleaning the white rust at this point may expose a large area of the steel substrate. Even if cleaned, the galvanized layer in that area has lost its protective ability, and the red rust will spread rapidly.
Cleaning method: Mechanical methods (such as wire brushes and sandpaper) are required for strong cleaning, but this method will damage the surrounding intact zinc layer. A secondary rust prevention treatment, such as spraying with zinc-rich paint, is necessary after cleaning; otherwise, the area will quickly rust again.
5.What are some recommended cleaning methods?
Recommended: Use non-metallic tools (soft cloth, brush, scouring pad) for dry or lightly damp cleaning. After cleaning, be sure to thoroughly dry the surface and ensure good ventilation to prevent the recurrence of white rust.
Not Recommended: Avoid using hard metal tools (such as steel wool, steel brushes), as this will severely scratch and remove the intact zinc layer, resulting in "over-cleaning" and doing more harm than good.
Use acid pickling with caution: Although dilute acids (such as acetic acid) can quickly dissolve white rust, it is extremely difficult to control and can easily over-corrode the intact zinc layer, causing the surface to blacken and become rough, severely impairing its corrosion resistance. Unless for professional treatment, its use is not recommended.