1.What is the anti-corrosion basis of the galvanized coil itself?
The zinc coating provides protection for the base steel sheet through sacrificial anode protection (zinc corrodes first) and physical barrier effect (isolating water and oxygen).
Standard galvanized coils usually have zinc coating on both sides (unless they are specially customized single-sided galvanized products). However, in some scenarios, the back coating may be slightly damaged (such as scratches and exposed bottom) due to processing (such as cutting and handling).
Therefore, under ideal conditions (complete coating and no damage), the back zinc coating itself has a certain anti-corrosion ability and no additional treatment is required.
2.Is it necessary to do back corrosion protection if the back coating is damaged or incomplete?
The processing process (such as shearing, stamping, welding) may cause the back coating to be scratched or peeled off, exposing the base steel plate. If it is not repaired, it will become the starting point of corrosion (especially in a humid environment).
Specially customized single-sided galvanized coils (only the front side has a coating, and the back side is a bare steel plate) have no protection on the back side and must be treated with anti-corrosion (such as painting, spraying).
3.What are the typical scenarios where the back side needs to be protected from corrosion?
Application in highly corrosive environments
If galvanized coils are used in humid, high-humidity environments (such as bathrooms and kitchen walls), industrial corrosive environments (such as chemical plants and coastal areas, containing salt and acid mist), or buried or underwater scenes, the zinc coating alone may not be enough to resist long-term corrosion:
The zinc coating consumes faster in highly corrosive environments, and if the back is exposed to corrosive media (such as condensed water on the back and salt in the soil), it may fail prematurely.
At this time, additional anti-corrosion is required on the back (such as coating epoxy primer, polyurethane topcoat, or pasting anti-corrosion tape) to extend the overall service life.
Scenario with extremely high requirements for anti-corrosion life
Some projects require an anti-corrosion life of more than 15 years. The simple galvanized layer may gradually fail after 10-15 years. Additional anti-corrosion on the back can form a "double protection" and significantly extend the life.
Scenarios where the back side may come into contact with electrolyte solution
If the back side of the galvanized coil may come into contact with electrolytes such as water, rainwater, and industrial waste liquid, even if the coating is intact, the micro-battery effect formed by the zinc layer and the substrate may accelerate local corrosion. Additional corrosion protection can isolate the electrolyte and block the corrosion reaction.
4.What are the scenarios where it is not necessary to do anti-corrosion on the back?
Application in ordinary dry environment
For indoor dry environment (such as furniture, inside of home appliance shell), the back side does not contact water or corrosive substances, the anti-corrosion ability of zinc coating itself is sufficient, and no additional treatment is required.
The back side is completely not exposed or physically isolated
If the back side of the galvanized coil is covered by other materials (such as walls, insulation layer), or is in a sealed environment (such as the side of the pipe that does not contact the medium), and there is no risk of moisture penetration, no anti-corrosion is required.
Sufficient zinc coating thickness and excellent quality
For thick zinc coating galvanized coils (such as zinc coating thickness > 200g/㎡), in general atmospheric environment (such as urban outdoor non-coastal areas), the back zinc layer can stably protect for more than 10 years without additional treatment.
5.What are the common treatment methods for back corrosion protection?
Painting: Economical choice, such as alkyd paint (suitable for dry environment), epoxy paint (moisture resistant), fluorocarbon paint (strong weather resistance).
Galvanized layer repair: For local damage, cold spray zinc paint with high zinc content or zinc powder primer can be used for repair.
Lamination/Laminating: Paste anti-corrosion film, PVC layer or rubber layer on the back to physically isolate the corrosive medium (suitable for mildly corrosive environment).