Walk into any steel yard in Coimbatore and ask for a galvanised sheet. Nine times out of ten, the guy behind the counter will stop and ask — "GP or GI?" And that's where most buyers go quiet.
It's not a trick question. But if you don't know the answer, you're about to make a decision that could cost you money — either through material that fails too soon, or extra labour fixing a surface that won't hold paint the way it should.
At Magnus Steels, we've had this conversation on the phone, at the yard, and on job sites across Coimbatore and Tamil Nadu for years. What you'll read here isn't pulled from a product datasheet — it comes from knowing what actually goes wrong when buyers choose in a hurry.
Both GP and GI sheets are galvanised — meaning a zinc layer is applied over mild steel to prevent rust. Zinc is the protective barrier here. It reacts with moisture and oxygen before the steel does, sacrificing itself so the base metal stays intact.
The difference is in how that zinc coating is applied and how thick it is. That's what separates GP from GI — and that's what determines which one fits your project.
This is the question we answer on the phone every day. The answer is simpler than most people expect.
| Feature | GP Sheet (Galvanised Plain) | GI Sheet (Galvanised Iron) |
|---|---|---|
| Galvanising Process | Electro-galvanising or light hot-dip | Hot-dip galvanising |
| Surface Finish | Smooth, flat, even | Rough, spangled (flower pattern) |
| Zinc Coating (GSM) | Thinner — 60 to 120 GSM | Thicker — 80 to 275+ GSM |
| Corrosion Resistance | Moderate — suited for indoor use | High — handles outdoor exposure |
| Paint Adhesion | Excellent — smooth surface holds paint well | Moderate — needs prep before painting |
| Formability | Excellent — easy to cut, bend, weld | Good — slightly stiffer due to coating |
| Cost | Generally lower | Slightly higher |
| Best For ⭐ | Indoors, fabrication, appliances, panels | Outdoors, roofing, coastal, heavy industrial |
Here's something that trips up a lot of buyers: gauge numbers run backwards. 16G is thicker than 20G. The higher the number, the thinner the sheet. Nobody tells you this when you first walk into a yard — you're just expected to know.
We've seen contractors order 24G for roofing because it was cheaper — only to have it dent and leak six months in. We've also seen panel fabricators order 16G when 22G would have done the job at half the weight and cost. The gauge decision isn't complicated, but it matters. Use this to get it right the first time.
| Gauge | Thickness (mm) | Weight (kg/sqm) | Typical Use |
|---|---|---|---|
| 16 G | 1.6 mm | ~12.6 | Heavy industrial roofing, structural cladding |
| 18 G | 1.2 mm | ~9.4 | Factory roofing, warehouse shed walls |
| 20 G | 1.0 mm | ~7.8 | Agricultural sheds, general roofing |
| 22 G | 0.8 mm | ~6.3 | Electrical panels, HVAC ducts, false ceilings |
| 24 G | 0.6 mm | ~4.7 | Light fabrication, interior partitions, enclosures |
| 26 G | 0.45 mm | ~3.5 | Lightweight cladding, decorative panels |
This is something buyers find out too late. You call a yard, agree on price, block a vehicle — then get told at dispatch that the size you want has to be cut specially and it'll take two more days. That's a problem when your site is waiting.
Here's what we keep in stock at Masakalipalayam, ready to go same day:
| Size (feet) | Size (mm) | Common Application |
|---|---|---|
| 6 × 4 ft | 1830 × 1220 mm | Fabrication, wide panels |
| 8 × 4 ft | 2440 × 1220 mm | Industrial roofing, cladding |
| 10 × 5 ft | 3050 × 1525 mm | Extra - wide,long span roofing |
Need a size that's not on this list? We do custom cutting for bulk orders. Call us with your exact dimensions before you finalize anything — we'll confirm what's in stock, what needs cutting, and what it'll cost. No surprises when the truck shows up.
GI sheets are the standard for roofing and wall cladding in factories, warehouses, and industrial sheds across Coimbatore's manufacturing belt. The thick zinc coating handles direct rain, heat, and humidity without breaking down — which is exactly what Tamil Nadu's climate demands from a roofing sheet.
GP sheets are the default choice for electrical enclosures, control panels, and distribution boards. The smooth, flat surface takes powder coating and paint without any grinding or prep — which saves real time on the shop floor for panel fabricators across Coimbatore's electrical industry.
For cattle sheds, crop storage, and any construction near the coast, GI sheets at 180 GSM and above are the right call. Salt air is unforgiving — lower zinc coatings fail faster than most buyers expect. This is a lesson that comes back expensive if you get it wrong the first time.
HVAC ducts, ventilation systems, and interior false ceilings rely on GP sheets because the material bends, cuts, and installs cleanly without cracking the coating. The smooth finish also reduces air resistance inside duct runs — a practical performance benefit, not just a surface preference.
We've seen this play out more than once. A workshop owner picks GP sheets for outdoor roofing because they're cheaper. The zinc coating — thinner by design — wears down within six months under rain and direct sun. Rust sets in. The sheets need to come down and be replaced. Everything they saved on material gets spent twice over on labour and new stock.
The reverse happens too. A fabricator orders GI sheets to build electrical panels. The spangled surface needs grinding and priming before paint will stick properly — adding labour hours that GP sheet would have cut out entirely.
The rule is simple: outdoors and weather exposure — go GI. Indoors, fabrication, and painted finishes — go GP. If you're not sure, call us before you order. It's a two-minute conversation that saves a much longer one later.
Steel prices shift with the market. Here's what genuinely moves the number on your invoice — and what to watch out for when you're comparing quotes:
If you've been searching online for a GI sheet dealer near you, here's the honest answer: don't just call whoever shows up first. Half the yards in Coimbatore stock one or two grades and call it a full range. You find out what's missing only after you've confirmed the order.
We operate out of Masakalipalayam, Coimbatore — and we stock GP and GI sheets across every gauge, GSM grade, and standard size. One call, one supplier, no running around. Here's where we deliver and how fast:
| Location | Delivery Time | Notes |
|---|---|---|
| Coimbatore city & outskirts | Same day | Order before noon for same-day dispatch |
| Tirupur | Next day | Regular delivery runs — confirm slot when ordering |
| Erode | Next day | Bulk orders prioritised |
| Salem | 24–48 hours | Coordinate with our team for scheduling |
| Pollachi | Same day / Next day | Frequent runs — call to confirm |
Before you drive to any yard — call ahead. Confirm the gauge, GSM, and size is sitting in stock. Call us at +91 80155 27611 and we'll sort it in one conversation — stock check, price, and delivery slot included.
GP and GI sheets might look identical on the shelf — but they're built for different environments and different jobs. Putting one where the other belongs doesn't just affect performance. It costs you money in rework, replacement, and time lost on site.
At Magnus Steels, we stock the full range across all thicknesses and GSM grades, quote transparently, and deliver across Coimbatore, Tirupur, Erode, and Salem. If your current supplier has been giving you the wrong grade or shifting prices between the call and the truck — give us one call. We'll show you what a straightforward steel supply relationship actually looks like.