STP ShaliPrime ZnSL
A zinc-rich ethyl silicate primer that lets structural steel protect itself, coat after coat, in the harshest corrosive and offshore environments.
What is it?
A two-component, moisture-curing zinc silicate primer on an inorganic ethyl silicate binder loaded with metallic zinc, built to stop corrosion at the steel surface rather than just seal it away.
Where is it used?
Structural steel, pipelines, storage tanks, offshore platforms, refineries, petrochemical units, power plants and fertiliser complexes — anywhere bare steel meets a genuinely hostile atmosphere.
Why use it?
The zinc sacrifices itself before the steel does, giving true cathodic protection rather than a physical barrier, and the inorganic binder shrugs off heat, solvents and abrasion that soften an ordinary organic primer.
How is it applied?
Mixed on site in a fixed binder-to-powder ratio with a drill mixer, then airless- or air-sprayed onto blast-cleaned steel, built up to the specified dry film thickness.
About STP ShaliPrime ZnSL
Bare structural steel starts corroding the moment it’s exposed, and on India’s refineries, ports and coastal EPC sites, that corrosion is a design load, not a background process. STP ShaliPrime ZnSL was built for exactly that: a two-component, moisture-curing zinc silicate primer where an inorganic ethyl silicate binder carries a very high loading of metallic zinc dust. Once cured, the zinc stays in electrical contact with the steel beneath, so the film acts less like paint and more like a sacrificial anode fused to the structure — the zinc corrodes first, and the steel doesn’t.
That’s why contractors specify it on steelwork that has to survive conditions that degrade conventional coatings — dry heat up to 400°C, splash-zone salt spray, solvent and abrasion exposure on process plant equipment. It complies with IS 14946-2001, mixes in a fixed 2:3 binder-to-powder ratio, and is applied by airless or air spray over blast-cleaned steel. At Space Arc it sits alongside STP’s wider primer and coating range, and pairs with a companion Fosroc zinc-rich primer for projects that also need to protect concrete rebar.
The technical insight
The difference comes down to binder chemistry, not just the zinc. Organic epoxy zinc-rich primers bind zinc dust in a resin that eventually softens under heat, solvents or strong chemicals. ShaliPrime ZnSL uses an ethyl silicate binder instead: on curing, moisture in the air reacts with the silicate to build a hard, glass-like silica matrix around the zinc rather than a polymer film. That’s what delivers the 400°C dry-heat tolerance and chemical resistance an organic primer can’t match. It also keeps the zinc in direct metal-to-metal contact with the steel, the actual precondition for cathodic protection — zinc trapped in resin can’t sacrifice itself, it just sits there as pigment. That’s why surface prep matters so much: a properly blasted surface gives the zinc a clean, conductive substrate; a poor one breaks that contact.
Where it is used
- Priming structural steel on refineries, petrochemical units and power plants
- Steel pipelines and pipe racks in industrial or coastal atmospheres
- Offshore platforms and steel in marine splash zones
- Exterior and interior steelwork on storage tanks
- Fertiliser plant structures exposed to acidic and alkaline fumes
- Bridges and long-span steel in severely corrosive environments
Key advantages
- True cathodic, sacrificial protection, not just a barrier coat
- Dry heat resistance up to 400°C from the inorganic binder
- Excellent salt spray resistance after 1000 hours at 75 microns DFT
- Excellent water, solvent and abrasion resistance, water-resistant within 30 minutes
- Very good alkali resistance and good acid resistance
- Made to IS 14946-2001 by an 85-year-old Indian company
Limitations & considerations
- Performance depends heavily on surface prep quality, since it governs the zinc-to-steel contact
- Two-component product: needs correct 2:3 drill-mixing and a 10-minute maturing time before use
- Pot life is short, about 5 hours at 30°C/50% RH, so mix only what you can use
- Solvent-based with a flash point just above 15°C — needs ventilation and fire precautions
- More porous than an epoxy primer, so DFT must be built up in controlled passes to avoid mud-cracking
- Minimum 12-hour wait before overcoating, which has to be planned into site schedules
Selection & best practice
Blast clean new steel to the specified profile (max 65 microns); where that’s impractical, use mechanical tools, chipping and wire brushing, then dust down with hot air. Mix Component B (zinc) into Component A with a drill mixer at 350–400 rpm until homogeneous, mature 10 minutes, and keep stirring through application. Spray to 60–75 micron DFT per coat rather than one heavy pass, to avoid mud-cracking, staying within the roughly 5-hour pot life and the 12-hour minimum before overcoating.
Specifications
| Chemistry | Two-component, moisture-cured zinc-rich ethyl silicate |
| Mixing Ratio (Binder : Powder) | 2 : 3 by weight |
| Theoretical Coverage | 8–10 m²/L at 60–75 micron DFT |
| Volume Solids | 60 ± 3% |
| Pot Life (30°C, 50% RH) | 5 ± 1 hours |
| Dry Heat Resistance | Up to 400°C |
| Adhesion (Pull-off, ASTM D4541) | > 5 MPa |
| Drying Time (27°C, 60% RH) | Surface dry 15 min; hard dry 2 hrs min; overcoat after 12 hrs min |
| Standard Compliance | IS 14946-2001 |
Industry use cases
Oil and Gas / Refineries
Primes structural steelwork, pipe racks and pipelines against fumes and humidity typical of refinery sites.
Power Plants
Steel at elevated operating temperatures, where 400°C dry-heat tolerance keeps the film intact through thermal cycling.
Ports, Jetties and Offshore Platforms
Steel in marine splash zones and coastal atmospheres where salt spray resistance is non-negotiable.
Fertiliser and Chemical Plants
Storage tank exteriors and interiors and structural steel exposed to acidic and alkaline fumes.
Frequently asked questions
Is this the same as an epoxy zinc-rich primer?
Do I need to topcoat it?
What surface prep does it need?
How is it mixed, and how long does the mix last?
How soon can the structure go back into service?
What pack size and shelf life should I plan for?
How we position STP ShaliPrime ZnSL
ShaliPrime ZnSL is STP’s heavy-duty answer to structural steel corrosion, usually the first coat in a bigger system rather than a stand-alone product. It pairs with STP’s epoxy intermediate coats and polyurethane topcoats for full multi-coat systems, and sits alongside STP’s lighter-duty primers for projects that don’t need the full zinc-silicate spec. Space Arc is also an authorised Fosroc distributor, so projects combining structural steel with concrete repair can source rebar-scale zinc protection from the Fosroc range on the same order.
Fosroc Fosroc Nitoprime Zincrich — Not a direct swap — Fosroc Nitoprime Zincrich is a single-component zinc-rich primer sized for exposed rebar in concrete repair, not heavy structural steelwork. Where a project needs both, it’s a natural companion for the reinforcement side while ShaliPrime ZnSL handles the primary steel structure.
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