In the world of steel roofing and cladding, colour coated sheets have become the go-to choice for industrial, commercial, and residential projects. They’re durable, visually appealing, and offer weather protection. But one of the most critical factors buyers often overlook is GSM — a term that can greatly impact the lifespan, performance, and cost of these sheets.
So, what exactly is GSM in colour coated sheets, and why does it matter for your project?
What is GSM ?
GSM stands for Grams per Square Meter. In the context of colour-coated steel sheets, it refers to the zinc coating weight applied to the base steel sheet during the galvanization process.
In simple terms:
GSM indicates how much zinc is coated on the surface of the sheet, both on the top and bottom.
Why is Zinc Coating important ?
Zinc acts as a protective shield that prevents the steel from rusting or corroding when exposed to moisture, rain, and chemicals. The thicker the zinc layer (i.e., higher GSM), the better the corrosion resistance of the sheet.
Common GSM Grades in India :
| GSM Ratings | Zinc Coating (per m2) | Usage /Application |
| 90 GSM | Light coating (45 top + 45 bottom) | Interior or low-corrosion environments |
| 120 GSM | Moderate coating | Warehouses, shops, and temporary sheds |
| 180 GSM | Heavy-duty coating | Factory sheds, houses, mid-level corrosion zones |
| 275 GSM | Premium protection | Coastal areas, high-rainfall zones, and industrial rooftops |
Note: The zinc layer is applied on both sides, and GSM includes the total of both.
Why GSM matters for your project ?
Choosing the right GSM rating ensures:
1. Longer Life Span
- A higher GSM sheet lasts 10–15 years longer than a lower GSM sheet in the same conditions.
- It minimizes rusting, pitting, and metal fatigue over time.
2. Better Protection in Harsh Environments
- In coastal or industrial areas, pollution and moisture accelerate corrosion.
- A 275 GSM sheet is highly recommended in such cases for longevity.
3. Cost Efficiency in the Long Run
- While higher GSM sheets may cost more initially, they reduce replacement and maintenance costs significantly.
4. Improved Structural Integrity
- Zinc-coated steel resists cracking and peeling of the paint layer, preserving the strength of the structure.
Does GSM Affect Colour Coating?
Yes, indirectly.
- A high-GSM base sheet offers better adhesion for primer and top coat paint layers.
- It improves the paint’s durability, reducing the risk of chipping or fading.
- This is crucial for branding, aesthetics, and heat-reflective finishes (like cool roofing).
What to Ask When Buying Colour Coated Sheets ?
Before purchasing, make sure to ask:
- What is the GSM rating of the sheets?
- Is the zinc coating uniform on both sides?
- Is it regular spangle or zero spangle finish?
- Are test reports or quality certificates available?
- What is the warranty or life expectancy in your location?
GSM vs Thickness – Are They the Same?
No. GSM is about coating weight, while thickness is the total depth of the steel sheet (including coating). You can have:
- 0.50 mm sheet with 120 GSM
- 0.50 mm sheet with 275 GSM
The base steel thickness may be the same, but their durability and price will differ due to coating.
Applications Based on GSM
| Application Area | Suggested GSM |
| Interior partitions & ceilings | 90-120 GSM |
| Factory Roofing (non-coastal) | 120-180 GSM |
| Coastal Factory/ Salt Zone | 275 GSM |
| Poultry Farms, Dairy Farms | 180-275 GSM |
| Schools, Warehouses, Offices | 120-180 GSM |
Shree Sai Steels Recommends
At Shree Sai Steels, we supply high-quality colour coated hi-rib sheets with options in:
- Thickness: 0.35 mm to 0.60 mm
- GSM: 90, 120, 180, 275
- Coatings: Regular or Zero Spangle, Chromated, and Passivated
- Colours: Brick Red, Blue, Green, Grey, and more
Our team helps customers choose the right combination based on their project location, usage, and budget.
Conclusion
Understanding GSM in colour-coated sheets is not just a technical detail — it’s a vital quality factor that affects the life, cost, and performance of your steel structure. Whether you’re constructing a factory, warehouse, home, or temporary shelter, always evaluate GSM before making a purchase.
Looking to buy high-GSM colour-coated roofing sheets?
Reach out to Shree Sai Steels for expert guidance and premium-quality products tailored to your project.
📞 Call us at 9810036937
🌐 Visit: shreesaisteels.com
