STP ShaliPrime PU MIO Zn
Single-pack moisture-cure polyurethane primer loaded with zinc and micaceous iron oxide — built to grip marginally prepared, flash-rusted steel and keep curing right through humid weather.
What is it?
A single-component, moisture-cured polyurethane anticorrosive primer from STP Limited, pigmented with zinc dust and micaceous iron oxide. Classified under SSPC PS 12.00 as a Type II B zinc-rich primer and compliant with SSPC Paint 20 Type II Level 3.
Where is it used?
Structural steel on bridges, refineries and chemical plants, offshore platforms, ports, pipelines, ballast and storage tank interiors, hydropower and wastewater facilities — wherever steel faces aggressive, humid or marine exposure.
Why use it?
It bonds to marginally prepared rusty steel and aged coatings, tolerates damp substrates and flash rusting, and has no induction time and no recoat window — so maintenance painting keeps moving in conditions that stall conventional two-pack primers.
How is it applied?
Brush, roller, conventional or airless spray over blast-cleaned steel (Sa 2 for atmospheric duty, Sa 2.5 for immersion). Theoretical coverage 6.5 m²/L at 100 micron DFT; keep steel temperature 4–5°C above the dew point.
About STP ShaliPrime PU MIO Zn
ShaliPrime PU MIO Zn answers a problem every maintenance painting contractor in India knows well: steel that cannot be blasted to bright metal, weather that never quite dries out, and shutdown windows too short for fussy two-pack systems. It is a single-component polyurethane primer that cures by reacting with atmospheric moisture — the humidity that ruins conventional primers actually drives its film formation. The binder carries a dual anticorrosive package of sacrificial zinc dust and lamellar micaceous iron oxide, and the formulation meets SSPC PS 12.00 as a Type II B zinc-rich primer, complying with SSPC Paint 20 Type II Level 3.
Space Arc Engineering supplies ShaliPrime PU MIO Zn across Delhi NCR and pan-India as an authorised STP distributor and applicator. We see it specified most often for maintenance repainting of bridges, refinery pipe racks, port equipment and plant steel — jobs where the existing coating is chalked but sound, access is expensive, and the engineer wants one surface-tolerant primer that works over marginal prep and old coatings alike. At 65 ± 3% volume solids it builds a useful film per coat, and its flat MIO-grey finish keys well for subsequent build coats.
The technical insight
The primer protects steel in two ways at once. Zinc dust in contact with the substrate is more electrochemically active than iron, so at scratches and pinholes it corrodes preferentially — cathodic protection that checks rust creep. Above it, micaceous iron oxide flakes align parallel to the surface as the film forms, stacking into an overlapping barrier that forces water, oxygen and chlorides to take a long, tortuous path to the steel. The moisture-cure urethane binder ties the system together: its isocyanate groups crosslink with ambient humidity, which is why the film tolerates damp substrates and flash rusting that would blister an epoxy — and why there is no induction time and no recoat limit between coats.
Where it is used
- Maintenance repainting of road and rail bridge steelwork
- Structural steel in refineries and chemical process plants
- Offshore platforms and marine-port facilities
- Ballast tanks and interiors of storage tanks
- Cross-country and in-plant pipelines
- Material handling equipment — conveyors, cranes, hoppers
- Hydropower and wastewater treatment plant steel
Key advantages
- Applies to moist substrates and tolerates flash rusting — work continues in humid or coastal conditions
- Bonds to marginally prepared rusty steel and most aged coatings, trimming surface-prep cost on maintenance jobs
- Dual protection in one primer coat: sacrificial zinc plus MIO barrier
- Single pack — no mixing ratios, no induction time, no pot-life wastage
- No recoat time limit, so staged or interrupted painting programmes never force reblasting
- High chemical resistance, excellent abrasion resistance and strong resistance to blistering
- 65 ± 3% volume solids for efficient film build; VOC compliant
Limitations & considerations
- Surface-tolerant is not prep-free: Sa 2 / SSPC-SP6 commercial blast remains the minimum, and immersion or severe exposure demands Sa 2.5 / SSPC-SP10
- Moisture-cure chemistry means part-used pails can skin and gel — plan quantities around the 20 L pail and reseal immediately
- Full cure takes 7 days, so immersion or aggressive service must be scheduled accordingly
- It is a flat-sheen grey primer, not a finish — compatible topcoats are needed for colour, gloss and UV durability
- Steel temperature must stay 4–5°C above the dew point during application to avoid condensation defects
- Thinning is restricted to STP Thinner; other solvents can destabilise the moisture-cure resin
Selection & best practice
Blast to Sa 2 (SSPC-SP6/NACE 3) for atmospheric exposure or Sa 2.5 (SSPC-SP10/NACE 2) for immersion, then clear dust, oil and loose particles with compressed air or brushing. Power-stir each pail thoroughly — zinc and MIO are heavy pigments that settle hard to the bottom. Apply by brush, roller or spray; thin only with STP Thinner, and only if conventional spray demands it. Work to 100 micron DFT per coat against the theoretical 6.5 m²/L, budgeting extra for profile and losses on pitted maintenance steel. Confirm steel temperature sits at least 4–5°C above the dew point before starting. Recoat whenever access allows — there is no maximum window — and give the film 7 days to reach full cure before aggressive service. Decant what you need and reseal fast: the pail cures on humidity just as the film does.
Specifications
| Resin type | Moisture-cure urethane, single component |
| Anticorrosive fillers | Zinc dust + micaceous iron oxide (MIO) |
| Classification | SSPC Paint 40 Type II; SSPC PS 12.00 Type II B; SSPC Paint 20 Type II Level 3 |
| Volume solids | 65 ± 3% |
| Theoretical coverage | 6.5 m²/L at 100 micron DFT (surface-condition dependent) |
| Sheen | Flat |
| Full cure | 7 days |
| Packing | 20 L pail |
| Shelf life | 12 months, unopened, in cool dry airtight storage |
Industry use cases
Bridges & Infrastructure
Maintenance repainting of girders, bearings and truss steel where full reblasting to bright metal is impractical and possession windows are short.
Oil, Gas & Petrochemical
Pipe racks, structural steel, pipelines and tank internals in refineries and chemical process plants exposed to aggressive industrial atmospheres.
Marine & Ports
Port cranes, jetty steel, offshore platforms and ballast tanks — chloride-laden air where sacrificial zinc protection earns its keep.
Power & Water
Hydropower and wastewater treatment facility steelwork operating in permanently damp, splash-prone environments.
Manufacturing & Material Handling
Conveyor structures, cranes and hoppers where abrasion resistance matters as much as corrosion protection.
Frequently asked questions
Can ShaliPrime PU MIO Zn be applied over rusted steel without blasting?
How much primer do I need per square metre?
Can it be applied during humid or monsoon conditions?
What is the recoat window, and does it need a topcoat?
How is it different from ShaliPrime MIO PU?
What pack size is available and how long does it keep?
How we position STP ShaliPrime PU MIO Zn
Within the STP range, ShaliPrime PU MIO Zn is the surface-tolerant, zinc-rich anchor of the moisture-cure primer family. Specify ShaliPrime MIO PU where the same MC-PU chemistry is wanted without zinc — for less severe exposures or as an MIO build coat over a zinc primer — and consider STP’s two-pack options such as ShaliPrime 2PU or ShaliPrime 2E SF on new-build steel where controlled blasting and mixing discipline are guaranteed. For protecting reinforcement inside concrete repairs — a different problem to structural steel — we stock Fosroc Nitoprime Zincrich alongside Fosroc’s Dekguard range for coating the concrete itself.
Fosroc Nitoprime Zincrich — Choose Nitoprime Zincrich when the steel needing protection is exposed rebar inside a concrete patch repair rather than structural steel in the open — it is the standard single-pack zinc-rich primer specified ahead of Fosroc repair mortars.
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Authorised distribution, technical advice & professional application across Delhi NCR and Pan-India.