STP ShaliPrime Etch
Two-component zinc tetroxy chromate etch primer that chemically keys galvanized and non-ferrous metal so topcoats grip instead of peeling — IS 5666 compliant, surface dry in 25-45 minutes.
What is it?
A low-viscosity two-component etch primer from STP Limited, based on zinc tetroxy chromate, that etches and primes smooth metal in one thin coat. Conforms to IS 5666.
Where is it used?
Galvanized sheets, GI roofing and ducting, zinc-coated steel and light-metal fabrications — anywhere paint has to hold onto smooth, passive metal.
Why use it?
Paint applied straight onto galvanizing peels within months; ShaliPrime Etch hands the topcoat a chemically keyed surface at 8-10 m² per litre per coat.
How is it applied?
Mix base and activator, then brush, roller or conventional spray onto cleaned, degreased metal at 8-12 micron DFT; surface dry in 25-45 minutes at 30°C.
About STP ShaliPrime Etch
Zinc galvanizing is excellent at protecting steel — and equally good at rejecting paint. The surface it presents is smooth, chemically passive and often carries processing residue, so conventional primers sit on top of it rather than bonding into it, and the first thermal cycle or handling knock starts the peeling. Anyone who has watched a freshly painted GI duct shed its finish within a season knows the problem. The established answer is an etch primer: an ultra-thin pretreatment that attacks the zinc surface chemically and leaves it keyed, passivated and ready to hold a coating.
ShaliPrime Etch is STP Limited’s two-component version of that answer — a low-viscosity primer based on zinc tetroxy chromate, conforming to IS 5666. Mixed on site from base and activator, it spreads at 8-10 m² per litre per coat and dries to a film just 8-12 microns thick: enough to transform adhesion without adding measurable build to fabricated components. Pot life is a practical 4-5 hours at 30°C and the surface is dry in under an hour. Space Arc Engineering supplies it in 5 L packs across Delhi NCR and pan-India, alongside the topcoat systems it is designed to anchor.
The technical insight
An etch primer does its real work in the first moments of contact. The activator carries an acidic component that bites into the smooth zinc, dissolving the outermost layer and micro-roughening it, while the zinc tetroxy chromate pigment reacts with the freshly exposed metal to lay down an insoluble chromate conversion layer. That layer is chemically bonded to the substrate, passivates it against white-rust formation, and gives the thin resin film drying above it an anchor that mechanical abrasion alone cannot match. This is also why the volume solids figure of 9-10% looks low beside ordinary primers: the product is engineered to deposit a reactive film measured in single-digit microns, because in etch priming a thicker film is a weaker one.
Where it is used
- Priming galvanized roofing and wall-cladding sheets before decorative or protective topcoats
- GI ducting and HVAC sheet-metal work that must be painted after installation
- New galvanized steel water tanks ahead of internal or external coating systems
- Zinc-coated purlins, cable trays, enclosures and other building-services metalwork
- Aluminium and light-metal fabrications where conventional primers will not hold
- Pre-treatment of metal sheet before epoxy, PU or bituminous coating systems
- Repainting contracts where old finishes are ground back to sound galvanizing
Key advantages
- Chemically etches the zinc surface rather than relying on mechanical grip alone
- Better adhesion with retained flexibility, so the film moves with thin sheet metal
- Thin 8-12 micron DFT adds no measurable build or weight to fabricated components
- High coverage of 8-10 m² per litre per coat keeps the treated cost per square metre low
- 4-5 hour pot life at 30°C — one mixed batch lasts most of a working shift
- Surface dry in 25-45 minutes, so topcoating can proceed the same day
- Applies by brush, roller or conventional spray with ordinary site equipment
- Conforms to IS 5666, making it straightforward to specify on Indian projects
Limitations & considerations
- Not a primer for bare mild steel — it is formulated for galvanized and non-ferrous surfaces
- Chromate-based chemistry demands strict PPE and ventilation, and rules it out where a chromate-free specification applies
- At 9-10% volume solids it is a pretreatment, not a barrier coat — it must always be topcoated
- Shelf life is 6 months unopened, shorter than most primers, so order against firm requirements
- Theoretical coverage assumes good surface condition and falls on weathered or profiled sheet
Selection & best practice
Surface preparation decides the outcome. Remove dust, flakes, oil, grease and loose particles by sand blasting, wire brushing or compressed air, and take off old paint with a surface grinder — the primer must meet clean, dry, sound metal. For mixing, stir component A with a spiral-blade drill mixer at 300-400 rpm until homogeneous, let it stand 5 minutes so entrapped air escapes, then blend in component B slowly until fully dispersed. Apply one thin, continuous coat by brush, roller or conventional spray and resist the urge to build film: extra microns weaken an etch primer rather than strengthen it. Topcoat after the surface dries (25-45 minutes at 30°C) rather than leaving primed metal exposed, and mix only what the crew can place within the 4-5 hour pot life.
Specifications
| Product type | Two-component (2K) etch primer, zinc tetroxy chromate based |
| Standard compliance | Conforms to IS 5666 |
| Specific gravity | 1.20 ± 0.05 |
| Pot life at 30°C | 4-5 hours |
| Surface dry at 30°C | 25-45 minutes |
| Theoretical coverage | 8-10 m²/L per coat (surface-condition dependent) |
| Dry film thickness | 8-12 microns per coat |
| Volume solids | 9-10% |
| Packing / shelf life | 5 L container; 6 months in original unopened condition |
Industry use cases
HVAC & Building Services
Contractors painting GI ducting, dampers and trunking in malls, hospitals and IT parks add a quick etch-prime pass so identification and finish coats stop flaking off smooth zinc.
Pre-Engineered Buildings & Industrial Sheds
PEB erectors prime galvanized roofing, cladding and purlins before site-applied finish systems, closing off the classic warranty claim for peeling paint.
Water Storage & Utilities
New galvanized steel tanks are etch-primed before protective coating systems, giving barrier coats a keyed, passivated substrate to build on.
Electrical & Infrastructure
Cable trays, GI enclosures, poles and plant-room metalwork receive an 8-12 micron etch coat before epoxy or PU finishes in switchyards and substations.
Metal Fabrication Workshops
Job shops finishing aluminium and light-gauge zinc-coated fabrications standardise on a 2K etch primer to stop rejected batches caused by adhesion failure.
Frequently asked questions
Can I use ShaliPrime Etch on bare mild steel?
How long before the topcoat can go on?
Is an 8-12 micron film really enough?
What coverage should I budget?
How should a new galvanized surface be prepared?
What pack size is it supplied in and how do I store it?
How we position STP ShaliPrime Etch
ShaliPrime Etch is the specialist in STP’s primer family: reach for it when the substrate is galvanized or non-ferrous. For rusted iron and steel, its stablemate ShaliPrime RC converts rust into a stable primed layer instead of etching zinc, and STP’s protective and anti-corrosive coating range supplies compatible finish systems for the primed surface. Where the job is exposed steel reinforcement in concrete repair, specify Fosroc Nitozinc Primer, a zinc-rich epoxy Space Arc also stocks. We support all of these with TDS-level guidance and pan-India delivery.
Fosroc Nitozinc Primer — Specify Nitozinc Primer when the substrate is bare or exposed steel — such as reinforcement in concrete repair — where galvanic zinc-rich protection is needed and an etch primer for galvanized metal would be the wrong tool.
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