GI Sheets vs. Regular Steel Sheets: What Makes Galvanization Crucial for Longevity?
- Fortran Steel
- Dec 9, 2025
- 7 min read
Galvanized Iron (GI) sheets have become a preferred choice across construction, roofing, HVAC, automotive, and industrial sectors because they offer far better durability than regular steel sheets. By coating steel with a protective layer of zinc, GI sheets gain strong corrosion resistance, longer service life, and better performance in harsh environments. Compared to untreated galvanized steel sheets, non-coated MS sheets rust faster and require frequent maintenance. This guide explains the difference between GI sheets and regular steel, how zinc coating works, coating thickness (G40–G90), performance in demanding climates, and how to choose the right GI sheet supplier for long-term reliability.
Table Of Contents
What Are GI Sheets?
GI sheets (Galvanized Iron sheets) are steel sheets coated with a protective zinc layer to prevent rust. This zinc layer forms a barrier against moisture, chemicals, and environmental damage, making galvanized steel sheets far more durable than untreated mild steel. The galvanization process strengthens the base metal, improves its corrosion resistance, and increases its service life in outdoor or high-moisture environments.
Because of this protective layer, zinc-coated steel sheets are widely used in roofing, ducting, HVAC systems, PEB structures, fencing, and general construction where long-term corrosion resistance is essential.
Difference Between GI Sheets & Regular MS Sheets
The significant difference between GI metal sheets and regular mild steel sheets lies in their rust resistance. GI sheets have a zinc coating that protects the steel, whereas plain MS sheets are left uncoated and are vulnerable to moisture, oxidation, and other environmental damage.
GI Sheets vs Regular Steel Sheets
Feature | GI Sheets | Regular MS Sheets |
Rusting | Very slow due to the zinc coating | Fast, especially in moisture |
Protection | Barrier + sacrificial zinc layer | No protective layer |
Maintenance | Low | High (frequent repainting) |
Lifespan | Long-term durability | Shorter service life |
Ideal Use | Roofing, HVAC, PEB, outdoor structures | Indoor fabrication, general use |
Because untreated steel is prone to rust, galvanized steel performs significantly better in real-world conditions.
Read Next- Galvanized Steel vs. Stainless Steel
Zinc Coating: How It Prevents Corrosion
The main reason GI sheets last longer than regular steel is the zinc coating. This coating forms a strong galvanic layer that protects the base steel from moisture, oxygen, and other corrosive agents. Unlike paint, zinc metallurgically bonds to steel, forming a durable protective surface.
How Zinc Prevents Corrosion?
Barrier protection: Zinc blocks direct contact between steel and the environment.
Sacrificial protection: Zinc corrodes first, protecting the steel underneath.
Self-healing action: Minor scratches are protected by nearby zinc.
Because of these galvanization benefits, GI sheets are widely used as anti-corrosion steel sheets in outdoor, industrial, and high-humidity applications.
Hot-Dip vs Electro-Galvanization
Feature | Hot-Dip Galvanization | Electro-Galvanization |
Process | Steel dipped in molten zinc | Zinc is applied using an electric current |
Zinc Coating Thickness | Thicker, heavier coating | Thinner coating |
Corrosion Resistance | High | Moderate |
Surface Finish | Visible zinc spangle finish | Smooth, uniform surface |
Durability | Long-lasting protection | Shorter lifespan |
Best For | Roofing, cladding, HVAC, outdoor structures | Indoor parts, light fabrication |
Cost | Slightly higher | Lower |
Common Usage | Hot-dipped galvanized sheets for industrial & construction use | Appliances, panels |
GI Coating Thickness (G40–G90 / GSM) Explained
The durability of GI sheets largely depends on the amount of zinc applied to the steel surface. This is called GI coating mass, usually measured in GSM (grams per square metre). Simply put, higher GSM indicates a thicker zinc layer and better corrosion protection.
Many buyers also see coating grades written as G40, G60, or G90. These grades indicate the zinc coating level as defined under ASTM galvanization standards and broadly correspond to GSM values used in India.
What Coating Thickness Really Means
Lower GSM → Suitable for indoor or low-moisture environments
Medium GSM → Good balance of cost and corrosion resistance
Higher GSM → Best choice for outdoor, coastal, or industrial exposure
Read Next- How to Select the Right Steel Grade for Your Project
GI Coating Thickness Guide
Coating Level | Zinc Coating (Approx.) | What It’s Best Used For |
80 GSM (G40) | Light coating | Indoor panels, light fabrication |
120 GSM (G60) | Medium coating | Roofing, cladding, HVAC systems |
275 GSM (G90) | Heavy coating | Coastal areas, industrial buildings, long-life structures |
How does this apply to Fortran Steel GI Sheets?
Fortran Steel supplies GI Sheets & Coils with 80 GSM, 120 GSM, and 275 GSM zinc coatings, manufactured in accordance with IS 277-2018. This range allows buyers to select the right gi sheet coating thickness based on environment, expected service life, and maintenance requirements.
Choosing the correct coating mass is one of the most important steps in ensuring long-lasting performance from galvanized steel.
GI Sheet Life vs Non-Coated Steel
The biggest advantage of GI sheets over regular steel is their longer service life. Non-coated mild steel starts regular steel rusting as soon as it is exposed to moisture, air, or humidity. Over time, this leads to surface damage, loss of strength, and frequent maintenance.
GI sheets, on the other hand, are corrosion-resistant steel sheets because the zinc coating protects the steel beneath. Zinc corrodes first, slowing rust formation on the base metal. This protection significantly improves GI life expectancy, especially in outdoor and high-moisture environments.
Typical Life Comparison
Regular MS sheets: Shorter life, frequent repainting or replacement
GI sheets: Longer life with minimal maintenance
Performance in Coastal, Industrial & High-Moisture Areas
Environmental conditions play a major role in how steel performs over time. In coastal, industrial, and high-moisture areas, exposure to salt, humidity, chemicals, and condensation accelerates corrosion in regular steel.
This is where galvanized steel sheets perform significantly better. The zinc layer on zinc-coated steel sheets acts as a protective shield against moisture and airborne contaminants.
Even when the surface is scratched, zinc continues to protect the base steel through sacrificial action. Because of this behaviour, GI sheets are widely used as anti-corrosion steel sheets in coastal buildings, factories, warehouses, and HVAC installations.
For environments with constant moisture or chemical exposure, higher zinc coatings (such as 120 GSM or 275 GSM) provide longer service life and reduced maintenance.
GI Sheet Applications: Roofing, HVAC, PEB, Ducting
GI sheets are used across industries where corrosion resistance, durability, and low maintenance are essential. These GI sheet applications cover both outdoor and industrial environments.
1.Roofing & Cladding
GI roofing sheets are commonly used in residential, commercial, and industrial buildings. The zinc coating protects the steel from rain, heat, and humidity, making roofing gi sheets suitable for long-term outdoor exposure with minimal maintenance.
2.HVAC & Ducting
GI sheets are widely used for HVAC ducts and ventilation systems. Their smooth surface, corrosion resistance, and ease of fabrication help maintain airflow efficiency and structural stability over time.
3 Pre-Engineered Buildings (PEB)
In PEB structures, GI sheets are used for roofing and wall panels. Their strength-to-weight ratio and weather resistance make them ideal for large-span industrial and commercial buildings.
4.Other Industrial Applications
Apart from roofing and HVAC, GI sheets are also used in:
Fencing and agricultural structures
Storage sheds and enclosures
Electrical panels and appliance housings
General construction components
These applications highlight why GI sheets are preferred over regular steel in demanding environments.
How to Test GI Coating Quality?
Testing the zinc coating is important to ensure GI sheets provide adequate corrosion resistance and a long service life. Quality checks confirm that the galvanized layer meets the required standards.
1.Coating Mass (GSM) Test
This test measures the mass of the GI coating in grams per square metre. It confirms whether the sheet meets the specified coating level, such as 80 GSM, 120 GSM, or 275 GSM. Higher GSM values indicate stronger corrosion protection.
2.Coating Thickness Measurement
A magnetic or electronic gauge is used to measure zinc thickness across the sheet surface. Uniform readings indicate consistent coating quality.
3.Bend Test
The sheet is bent to check whether the zinc layer cracks or peels. A good-quality GI sheet maintains coating adhesion during bending.
4.Visual Surface Inspection
The surface is checked for uniform zinc coverage, coating defects, or uneven areas. A consistent finish indicates proper galvanization.
5.Standards Compliance Check
GI sheets should comply with ASTM galvanization standards or Indian standards such as IS 277. Certification confirms coating quality, durability, and batch traceability.
Choosing the Right GI Sheet Supplier in India?
Selecting the right GI sheet supplier is important for ensuring consistent quality, correct coating thickness, and long-term performance. Reliable GI sheet suppliers in India should offer certified materials, multiple GSM options, and compliance with standards like IS 277-2018.
Fortran Steel supplies high-quality GI Sheets & Coils in 80, 120, and 275 GSM, suitable for roofing, HVAC, cladding, and industrial use. With a wide size range, consistent coating quality, and timely B2B delivery, Fortran Steel supports project reliability from start to finish. If you need verified specifications or a bulk supply, contact Fortran Steel to discuss your GI sheet requirements and get a quote.
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Conclusion
GI sheets offer a clear advantage over standard steel by providing long-term corrosion resistance, reduced maintenance, and improved performance in demanding environments. From zinc coating methods and coating thickness to real-world applications and supplier selection, understanding these factors helps buyers make informed decisions. When sourced from a reliable supplier and selected for the right GSM and standards, GI sheets deliver durability, cost efficiency, and a dependable service life across roofing, HVAC, PEB, and industrial applications. Selecting the right GI sheet today ensures stronger, longer-lasting structures tomorrow.
FAQS
Q1. How long do GI sheets last compared to MS sheets?
GI sheets last significantly longer than regular MS sheets because the zinc coating protects the steel from corrosion. While untreated MS sheets may begin to rust within a few years in moist conditions, GI sheets can last 15–25 years or more, depending on coating thickness and environmental conditions. This improved GI life expectancy makes them suitable for roofing and outdoor applications.
Q2. Why does zinc coating prevent rust?
Zinc coating prevents rust by forming a protective barrier between steel and moisture. In addition, zinc corrodes before steel, offering sacrificial protection even if the surface is scratched. This mechanism is why galvanized steel sheets perform better than regular steel in humid and industrial environments.
Q3. What GI coating thickness should I choose?
The appropriate coating thickness depends on the application. Lower-gauge coatings, such as 80 GSM, are suitable for indoor or low-exposure areas, while 120 GSM works well for general roofing and cladding. For coastal or industrial environments, 275 GSM offers greater corrosion resistance and a longer service life.
Q4. Are GI sheets suitable for coastal regions?
Yes, GI sheets are suitable for coastal regions when higher zinc coatings are used. In salt-rich, high-moisture environments, zinc-coated steel sheets with 120 GSM or 275 GSM coatings perform better and resist corrosion more effectively than standard steel.
Q5. Do GI sheets require maintenance?
GI sheets require much less maintenance than MS sheets. The zinc coating protects the surface, reducing the need for frequent painting or rust treatment. Periodic inspection and cleaning are usually enough to maintain performance over time.
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