STP ShaliPrime MIO PU
Single-component, moisture-cured polyurethane primer loaded with micaceous iron oxide — a lamellar barrier for structural steel and concrete that clears 1,000 hours of salt-spray testing.
What is it?
A single-pack, moisture-cured aromatic urethane primer filled with micaceous iron oxide (MIO) and hydrophobic resins, giving barrier-type corrosion protection on steel and concrete.
Where is it used?
Bridges, pipelines, ballast tanks, offshore platforms, ports, refineries, power and wastewater plants, cooling towers and other large steel or concrete structures.
Why use it?
Passes 1,000 hours of salt spray at 200 micron DFT, pulls off at over 8 MPa on steel, tolerates flash rust and recoats most aged coatings — with no mixing or induction time on site.
How is it applied?
Airless spray, brush or roller in two coats of 100-110 microns each (200 microns total DFT), recoating at 6-10 hours; theoretical coverage 6.5 sq m per litre at 100 microns.
About STP ShaliPrime MIO PU
ShaliPrime MIO PU is STP Limited’s workhorse primer for steel that has to survive aggressive exposure. It is a single-component aromatic urethane that cures with atmospheric humidity, pigmented with micaceous iron oxide and reinforced with hydrophobic aromatic resins. Because there is nothing to proportion or induct, a maintenance crew can open the drum, stir, and start spraying — a real advantage on bridge decks, pipe racks and jetty steel where two-pack primers routinely get mixed wrong or exceed pot life in Indian summer temperatures.
The pinkish-red film builds 100-110 microns per coat at 65 percent volume solids, so a full 200-micron system needs only two passes. Verified test data backs the barrier claim: 1,000 hours of salt-spray endurance at 200 microns (ASTM B 117), pull-off adhesion above 8 MPa on blasted steel (ASTM D 4541), and abrasion loss under 0.2 g on the Taber test. Space Arc Engineering stocks the 20-litre drums for Delhi NCR and dispatches pan-India, with applicator crews available for blast-and-prime packages.
The technical insight
Two mechanisms work together here. First, the moisture-cure chemistry: free isocyanate groups in the urethane prepolymer react with ambient humidity to crosslink the film, which is why the primer needs no hardener and actually exploits the moisture that sabotages many coatings — flash-rusted steel is tolerable. Second, the MIO pigment: micaceous iron oxide is a plate-like, chemically inert mineral. As the film cures, these flakes lie down in overlapping layers parallel to the substrate, forcing water, oxygen and chloride ions to travel a long, tortuous path before reaching steel. That lamellar barrier is what shows up in the numbers — 1,000-hour salt-spray endurance and cathodic disbondment limited to 6 mm after 28 days (ASTM G 8) — while the urethane backbone keeps the film flexible (over 35 percent elongation) and impact-resistant to 60 kg-cm.
Where it is used
- Structural steel priming on bridges, flyovers and gantries
- Pipelines, pipe racks and tank exteriors in refineries and chemical plants
- Offshore platforms and marine-port facilities above the waterline
- Ballast tanks and material-handling equipment such as conveyors and chutes
- Power plants, cooling towers and wastewater treatment structures
- Large concrete structures needing a corrosion-resistant bonding primer
- Maintenance repainting over sound, aged coating systems
Key advantages
- Single pack with no induction time — stir and apply, no mixing-ratio errors on site
- Tolerant to flash rusting, so freshly blasted steel does not demand immediate coating
- Lamellar MIO barrier passes 1,000 hours salt spray at 200 micron DFT (ASTM B 117)
- Pull-off adhesion above 8 MPa on prepared steel (ASTM D 4541)
- Compatible with most old coatings, making it practical for maintenance overcoating
- High 65 percent volume solids — a 200 micron system in just two coats
- Resists chemicals, blistering and abrasion (under 0.2 g Taber loss, ASTM D 4060)
- Flexible, impact-resistant film: over 35 percent flexibility and 60 kg-cm direct impact
Limitations & considerations
- Solvent-borne with a 30 deg C flash point — flammable; needs ventilation and strict separation from hot work
- Aromatic urethane chemistry chalks and discolours under UV, so exposed work needs a compatible topcoat for appearance
- Do not apply below 5 deg C ambient, and substrate moisture must stay under 4 percent
- Recoat window is 6-10 hours; a missed window means abrading the surface before the next coat
- Short 6-month shelf life, and once opened the moisture-cure material can skin over in the drum
- Supplied only in 20 L MS drums — no small packs for touch-up quantities
Selection & best practice
Blast steel to SA 2-1/2 by shot blasting or mechanical grinding; loose scale, oil and grease must go first. On concrete, repair honeycombs with a polymer-modified mortar (ShaliCrete : cement : sand at 1:2:5) and confirm moisture is below 4 percent — a surface dry of condensation is non-negotiable. Stir the drum with a slow-speed mixer at roughly 400 rpm until homogeneous, then let it stand briefly so entrapped air escapes. Apply by single-component airless spray, brush or roller at 100-110 microns per coat, placing the second coat within the 6-10 hour recoat window to reach 200 microns total. Avoid thinning; if unavoidable, use only STP PU Thinner. Keep ambient temperature above 5 deg C and clean all tools immediately with STP Thinner — cured material will not redissolve.
Specifications
| Chemistry | Single-component, moisture-cured aromatic urethane with micaceous iron oxide; pinkish red |
| Density | 1.34 +/- 0.02 g/cc |
| Volume solids | 65 +/- 2% (ASTM D 2369) |
| Theoretical coverage | 6.5 sq m/L at 100 micron DFT (practical coverage varies with surface porosity and method) |
| Recommended DFT | 100-110 microns per coat; 200 microns total in two coats |
| Drying (24 deg C, 60% RH) | Touch dry 2.5 h; recoat 6-10 h; full cure 7 days |
| Adhesion (pull-off, steel) | >8 MPa (ASTM D 4541) |
| Salt-spray resistance | Passes 1,000 h at 200 micron DFT (ASTM B 117); cathodic disbondment 6 mm at 28 days (ASTM G 8) |
| Packing / shelf life | 20 L MS drum; 6 months sealed, stored cool and under shed |
Industry use cases
Bridges & Flyovers
Primes girders, bearings-zone steel and gantries where chloride-laden runoff and vehicle spray attack coatings; flash-rust tolerance suits phased blasting on live corridors.
Oil, Gas & Refineries
Barrier primer for pipelines, pipe racks and tank exteriors in chemically aggressive plant atmospheres, with abrasion resistance for maintenance traffic.
Marine & Ports
Above-waterline jetty steel, cranes, ballast tanks and offshore platform structures — the duty the 1,000-hour salt-spray rating is built for.
Power & Water Infrastructure
Structural steel and large concrete elements at power stations, cooling towers and wastewater treatment plants exposed to humid, corrosive service.
Industrial Plants & Material Handling
Conveyor structures, chutes and plant steel where impact (60 kg-cm) and abrasion resistance matter as much as corrosion protection.
Frequently asked questions
How much area will one 20 L drum cover?
Does ShaliPrime MIO PU need a topcoat?
Can it be applied on concrete as well as steel?
What surface preparation does steel need?
What is the recoat interval between coats?
How is this different from a zinc-rich primer?
How we position STP ShaliPrime MIO PU
Within the STP family, ShaliPrime MIO PU slots in as the steel-protection primer: pair it with STP PU Thinner for tool cleaning and any unavoidable thinning, and use ShaliCrete-modified mortar to reinstate concrete substrates before priming. Where a project specifies a two-component polyurethane primer instead, STP’s ShaliPrime 2PU covers that requirement. Space Arc also supplies competing steel-primer chemistries — including Fosroc’s zinc phosphate option — so specifiers can match the primer to the blast standard, exposure class and topcoat system actually available on site rather than force-fit one product.
Fosroc Nitozinc Primer — Specifiers running a Fosroc topcoat system on structural steel, or whose specification calls for a conventional single-pack zinc phosphate primer rather than an MIO barrier type, would pick Nitozinc Primer instead.
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