STP ShaliPrime Zn R
A two-component, cold-cure zinc-rich epoxy primer that protects structural and reinforcement steel by sacrificial cathodic action, not just a barrier film.
What is it?
A 2K cold-cure epoxy primer heavily loaded with zinc powder that shields steel through sacrificial cathodic protection, conforming to IS:14589-1999.
Where is it used?
Blast-cleaned structural steelwork, fabricated sections, plant and tank steel, and exposed reinforcement in concrete repair across industrial and coastal projects.
Why use it?
The zinc pigment corrodes in place of the steel, so protection continues even where the film is later scratched or damaged, well beyond what a plain barrier epoxy offers.
How is it applied?
Mix Component A with Component B, then brush, roller or airless-spray onto bone-dry, prepared steel at 40-45 microns DFT before applying the chosen topcoat.
About STP ShaliPrime Zn R
STP ShaliPrime Zn R is the anti-corrosive foundation coat that most steel protection systems are built on. It arrives as two parts, a zinc-loaded epoxy resin base and a matched hardener, that you blend on site and apply to freshly prepared steel. Ordinary paints and barrier epoxies fight rust by simply sealing moisture out, which works only until the film is nicked or worn. ShaliPrime Zn R takes a different route: the dense zinc content stays electrically active against the steel underneath, so the primer keeps defending the metal even after the coating is breached. That single behaviour is why specifiers reach for a zinc-rich primer on assets that have to last decades in humid, polluted or salt-laden air.
For engineers and contractors, the appeal is that it slots into how steel is actually detailed and fabricated in India. It goes down over blast-cleaned or mechanically prepared steel, cures at ambient temperature without heat or special curing regimes, and accepts conventional, two-pack epoxy or polyurethane topcoats once it has dried. That makes it equally at home as a shop primer during fabrication and as a site-applied primer during repair or refurbishment. The product conforms to IS:14589-1999 and, supplied and applied by Space Arc Engineering, is backed by the same distribution and application support we provide across our wider protective-coatings range.
The technical insight
The mechanism is galvanic. Because zinc sits above iron in the electrochemical series, the tightly packed zinc particles in the cured film become the anode and the steel becomes the cathode. When moisture and oxygen reach the surface, the zinc corrodes preferentially and the steel is left intact, exactly the principle behind hot-dip galvanising but delivered as a liquid coating. The film also builds a genuine barrier, so you get sacrificial protection and physical separation from the atmosphere in one coat. As the zinc slowly reacts it forms stable, insoluble zinc salts that partly seal the film and slow further consumption, extending service life. This is why STP records adhesion to metal above 1.5 MPa and why the coating is durable enough to carry a decorative or chemically resistant topcoat for the long term.
Where it is used
- Priming blast-cleaned structural steelwork before epoxy or polyurethane topcoats
- Shop priming of fabricated steel sections and built-up members during production
- Anti-corrosive priming of exposed reinforcement steel within concrete repair systems
- Protection of plant steel, walkways, gratings and support structures in process industries
- Priming of storage tanks, pipe racks and equipment steel in general to severe industrial atmospheres
- Touch-up and re-priming of damaged coatings during maintenance and refurbishment
- Steelwork in coastal and high-humidity environments needing sacrificial protection
- First coat in multi-layer protective systems for bridges, sheds and industrial buildings
Key advantages
- Sacrificial cathodic protection keeps guarding steel even where the film is scratched or damaged
- Conforms to IS:14589-1999, giving specifiers a recognised reference standard
- Cold-cure chemistry sets at ambient temperature with no heat or special curing needed
- Long 3-6 hour pot life gives ample working time on larger areas
- Overcoatable with conventional, two-pack epoxy or polyurethane topcoats
- Fast 1.5 hour surface dry keeps fabrication and site programmes moving
- Applies equally well by brush, roller or airless spray to suit the job
- Strong adhesion to prepared steel, measured above 1.5 MPa
Limitations & considerations
- Performance depends on proper surface preparation; blast cleaning to a profile not exceeding 65 microns is expected on new steel
- Two-component product with a limited pot life, so only mix what can be used within the working window
- Must be applied to a bone-dry surface between 10°C and roughly 50°C, not in the wet or in extreme heat
- Single-coat DFT is capped at 50 microns; heavier builds must be applied in multiple coats
- Not a finish coat on its own for aesthetic or aggressive chemical exposure; a suitable topcoat is required
- Tools and equipment need epoxy-thinner cleaning immediately after use to avoid hardening in place
Selection & best practice
Start with preparation, because the zinc can only work if it is in intimate contact with clean steel. Remove dust, flakes and loose rust; blast-clean new steel to a profile not exceeding 65 microns, or use mechanical tools, chipping and wire brushing where blasting is impractical, then dust down thoroughly. Stir Components A and B separately to redisperse any settled filler, add the whole of Component B into Component A and mix for about three minutes with a slow 400-500 rpm paddle until uniform. Apply to a bone-dry surface at roughly 5-6 m² per litre by brush or roller, or by airless spray using nozzle 327 with a 30-mesh filter at 110-160 kg/m² tip pressure. Keep each coat within 50 microns DFT and target 40-45 microns; apply the second coat only on a bone-dry first coat. Overcoat after 6-8 hours, though 12-24 hours is preferred for best performance. Clean all tools with epoxy thinner immediately, and use gloves, mask and eye protection with good ventilation throughout.
Specifications
| Composition | Two-component, cold-cure epoxy resin blended with zinc powder |
| Standard | Conforms to IS:14589-1999 |
| Specific Gravity | 1.50 +/- 0.02 |
| Pot Life | 3 – 6 hours |
| Surface Dry Time | 1.5 hours |
| Theoretical Coverage | 9 – 11 m2/L (surface dependent) |
| Recommended DFT | 40 – 45 microns (max 50 microns per coat) |
| Adhesion to Metal | Greater than 1.5 MPa |
| Pack Size | 15 L container |
Industry use cases
Structural Steel Fabrication
Used as a shop primer on blast-cleaned sections and built-up members so steel leaves the workshop already protected before topcoating.
Concrete Repair
Primes exposed reinforcement bars during patch repairs, stopping galvanic corrosion of the rebar before the repair mortar is reinstated.
Process and Chemical Plants
Protects walkways, gratings, pipe supports and equipment steel exposed to humid, polluted process atmospheres.
Coastal and Marine Structures
Provides sacrificial protection for steelwork in salt-laden air where barrier-only coatings tend to fail early at damage points.
Infrastructure Maintenance
Serves as a durable re-priming and touch-up coat during refurbishment of bridges, industrial sheds and storage installations.
Frequently asked questions
How is ShaliPrime Zn R different from an ordinary anti-rust primer?
What surface preparation does it need?
Can it be left as the final coat?
What DFT and coverage should I plan for?
How should it be applied and can it be sprayed?
What pack size and shelf life does it have?
How we position STP ShaliPrime Zn R
ShaliPrime Zn R is the standard-duty zinc-rich primer in STP’s range. Where the environment is more aggressive, marine or chemically loaded, step up to STP ShaliPrime Zn PE, the phenolic-epoxy variant that adds chemical resistance while keeping the same sacrificial zinc protection. Once primed, pair it with a compatible STP two-pack epoxy or polyurethane topcoat to complete the system. Buyers running Fosroc-based concrete repair should note that Fosroc’s own two-component zinc-rich equivalent, Nitozinc Primer, does the same job within the Renderoc repair system, so Space Arc can supply either family depending on your specification and site standard.
Fosroc Nitozinc Primer — Choose this two-component zinc-rich epoxy when the project is specified around Fosroc’s Renderoc concrete repair system and you want the primer and repair mortars from a single approved family.
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