■ Fundamentals
What Is Metal Coating?
Metal coating is the process of applying a protective or decorative layer to a metal substrate — steel, aluminum, iron, copper, or an alloy — to extend its service life, improve its performance, or enhance its appearance. A metal coating creates a physical barrier between the base metal and the environment, shielding it from moisture, oxygen, chemicals, abrasion, UV radiation, and temperature extremes that would otherwise cause corrosion, degradation, and structural failure.
The global metal coating market spans every sector of the economy. Infrastructure, manufacturing, energy, transportation, agriculture, defense, and construction all depend on correctly specified and applied metal coatings to keep assets operating safely and cost-effectively. When a coating fails on a pipeline, a bridge girder, a chemical storage tank, or a piece of heavy equipment, the cost of the resulting corrosion damage dwarfs whatever savings motivated the cheaper coating choice.
Plain-English Definition: Metal coating is any material — paint, epoxy, polyurea, polyurethane, zinc, galvanizing, powder coat, or ceramic — applied to a metal surface to protect it from corrosion, abrasion, impact, chemical attack, or weathering, or to improve its appearance or function.
Why the Right Coating Choice Matters
No coating chemistry is universally optimal. The correct choice depends on the substrate metal, the service environment, the expected mechanical and chemical loads, the required service life, the application method available, and the budget. A coating that performs perfectly on an interior structural steel beam may be completely inadequate for a marine splash zone or a chemical containment pad. This guide walks through every major variable so that contractors, engineers, and owners can make informed, defensible specification decisions.
4,500 psi
Tensile Strength
▪ Systems Overview
Types of Metal Coatings
The metal coating landscape includes dozens of chemistries and application methods. Understanding how each type works, where it excels, and where it falls short is the foundation of good specification practice. The six major categories below cover the coatings most commonly specified for structural steel, industrial equipment, storage tanks, pipelines, and heavy-duty infrastructure.
1. Polyurea Coatings
Polyurea is a spray-applied elastomeric coating formed by the reaction of an isocyanate component with an amine resin component. Applied through a heated, plural-component spray system, polyurea gels in seconds and reaches tack-free in minutes. The result is a seamless, flexible, high-strength membrane that bonds directly to properly prepared metal substrates.
Pure polyurea systems deliver industry-leading combinations of tensile strength (2,500–4,500 psi), elongation (300–600%), chemical resistance, and fast return to service. They perform across a temperature range from below freezing to over 300°F and resist saltwater, fuels, mild acids, alkalis, and most process chemicals. These properties make polyurea the premier coating system for metal surfaces that face mechanical, chemical, and environmental loads simultaneously.
2. Polyurethane Coatings
Polyurethane coatings are closely related to polyurea and share many performance characteristics. Pure polyurethanes react more slowly than pure polyureas, offering longer working times at the cost of slower productivity on large projects. Hybrid polyurea-polyurethane systems combine the fast reaction of polyurea with the longer pot life of polyurethane, balancing productivity and application flexibility. Aliphatic polyurethane topcoats are the standard finish for outdoor metal surfaces where UV stability and color retention are required.
3. Epoxy Coatings
Two-component epoxy coatings are the workhorse of industrial metal protection. Applied by brush, roller, or conventional spray, epoxies cure to a hard, dense film with excellent adhesion, chemical resistance, and abrasion resistance. Epoxies are the first choice for immersion service — tank linings, pipeline internal coatings, and marine hull coatings — where their resistance to cathodic disbondment and water absorption is critical. Their weakness is brittleness: epoxies crack under thermal cycling and impact loads that polyurea systems absorb elastically.
4. Zinc-Rich Primers & Hot-Dip Galvanizing
Zinc-based protection works by sacrificial corrosion: zinc corrodes preferentially to steel, protecting the base metal even through small holidays or damaged areas. Hot-dip galvanizing immerses fabricated steel in molten zinc to form a metallurgically bonded zinc-iron alloy coating. Zinc-rich primers achieve similar cathodic protection in a paint-on format and are routinely used as the first layer of a multi-coat system under epoxy or polyurea topcoats on bridges, transmission towers, and structural steel.
5. Alkyd and Acrylic Paints
Conventional alkyd and acrylic paints provide basic corrosion protection and decorative finish on metal surfaces in mild environments. They are lower in cost and easier to apply than high-performance industrial coatings. Their limitations are well-documented: lower build per coat, less chemical resistance, shorter service life, and higher sensitivity to surface preparation quality compared to epoxy, polyurethane, and polyurea systems. For industrial and commercial metal in demanding service, paint is a maintenance coating, not a protection system.
6. Powder Coatings
Powder coating applies a dry thermoset polymer powder electrostatically and cures it in an oven to form a hard, uniform film. Powder coatings deliver excellent appearance, edge coverage, and resistance to chipping on fabricated metal parts and architectural metalwork. Limitation: powder coating requires factory oven curing, making it impractical for field application on large structures, installed equipment, or complex geometries. It is the standard finish for architectural aluminum, appliances, automotive parts, and small fabricated steel components that can be sent through a coating line.
⚐ Surface Prep
Surface Preparation for Metal Coating
Surface preparation is the single most important variable in metal coating performance. The coating industry consensus is unambiguous: more coating failures are caused by inadequate surface preparation than by any other factor. A premium coating applied to a poorly prepared surface will fail prematurely. A commodity coating applied to a correctly prepared surface will outperform it. Invest in prep.
Surface preparation standards for metal coating are defined by SSPC (Society for Protective Coatings), NACE International (now AMPP), and ISO 8501. The standards define visual cleanliness grades and, for abrasive blasting, anchor profile depths. Matching the specified standard to the coating system is non-negotiable.
SSPC / NACE / ISO Blast Standards for Steel
| SSPC Standard |
NACE Equivalent |
ISO 8501 Grade |
Description |
Common Use |
| SSPC-SP 6 |
NACE 3 |
Sa 2 |
Commercial blast — at least 2/3 of surface free of visible contamination |
Atmospheric exposure, primer coats in mild service |
| SSPC-SP 10 |
NACE 2 |
Sa 2½ |
Near-white blast — at least 95% free of all visible residues |
Immersion service, polyurea, high-build epoxy, most industrial coatings |
| SSPC-SP 5 |
NACE 1 |
Sa 3 |
White metal blast — 100% free of all visible residues |
Nuclear, offshore, severe chemical immersion, highest-performance systems |
| SSPC-SP 11 |
NACE 7 |
— |
Power tool cleaning to bare metal — mechanical equivalent of blast |
Field touch-up, confined spaces where blasting is impractical |
Anchor Profile
Surface profile — also called anchor profile or surface roughness — is the microscopic peak-and-valley texture created by abrasive blasting. It is measured in mils (thousandths of an inch) using replica tape (Testex) or digital profilometers per ASTM D4417. The profile mechanically locks the coating to the metal surface. If the profile is too shallow, adhesion is reduced. If it is too deep, peaks can project through thin coatings and create corrosion initiation sites.
- 1.5–2.5 mil profile: Suitable for thin-film coatings, zinc primers, and conventional paints
- 2.5–4.0 mil profile: Standard for epoxy, polyurethane, and polyurea industrial systems
- 3.0–5.0 mil profile: High-build polyurea, tank linings, and heavy-duty immersion service
Contamination Control
Surface cleanliness includes more than rust and mill scale removal. Before any high-performance coating is applied to metal, the surface must be free of oil, grease, and wax (SSPC-SP 1 solvent cleaning), salts (measured by Bresle patch or equivalent; typically must be below 3–7 μg/cm² chloride), dust (tape test per ISO 8502-3), and moisture (dew point margin of at least 5°F above the substrate temperature must be maintained during application).
ArmorThane Standard: For polyurea direct-to-steel applications, ArmorThane requires SSPC-SP 10 near-white metal blast minimum, a 2.5–4.0 mil anchor profile, and application of an ArmorThane-specified primer before topcoat. This preparation protocol is documented on the Technical Data Sheet for each system.
⚙ How It Works
Polyurea & Polyurethane Systems for Metal
ArmorThane has been formulating pure polyurea and hybrid polyurea-polyurethane systems in Springfield, Missouri since 1989. We manufacture the coating chemistry, the application equipment, and the accessories — all under one roof. We train and support a global applicator network across more than 30 countries. We are not a franchise. There are no franchise fees. You get the manufacturer.
Our polyurea systems for metal coating are engineered for real-world service: abrasion from aggregate and debris, impact from equipment, immersion in process fluids, thermal cycling from −40°F to 300°F+, atmospheric corrosion from salt spray and industrial pollutants, and UV exposure in outdoor applications. The properties that make polyurea the dominant choice for metal protection are chemically fundamental, not marketing claims.
Why Polyurea Outperforms Other Metal Coatings
Seamless, Pinhole-Free Film
Sprayed wet-on-wet with no seams, no lap joints, and no brush marks. The membrane conforms to every curve, weld, rivet, and penetration. No point of entry for moisture or corrosive agents.
Extremely Fast Cure
Gel time of 3–15 seconds. Tack-free in under 2 minutes. Return to service in 1–24 hours depending on the system. No waiting days for coats to dry before the next application or before equipment returns to service.
Elastomeric Flexibility
300–600% elongation at break. Polyurea flexes with metal as it thermally expands and contracts. Epoxy and brittle coatings crack; polyurea does not. Essential for structural steel, pipelines, and tanks that cycle with temperature.
Superior Adhesion
Over a correctly prepared and primed metal surface, ArmorThane polyurea achieves pull-off adhesion values exceeding 1,500 psi — typically greater than the cohesive strength of the substrate. The coating fails in the substrate before it fails at the interface.
Moisture-Insensitive Cure
Unlike moisture-cure urethanes and some epoxies, polyurea reaction chemistry is relatively insensitive to ambient humidity. This makes field application practical in humid environments where competing coatings would blush, bubble, or lose adhesion.
100% Solids — Zero VOC
ArmorThane polyurea systems contain no solvents. 100% of what goes on the gun stays in the film. Zero VOC emissions. Meets air quality regulations in all 50 states without permits or restrictions, and eliminates solvent-handling hazards on the job site.
ArmorThane Product Systems for Metal Coating
HighLine 510H — Pure Polyurea for Metal
HighLine 510H is a two-component, 100% solids, pure polyurea elastomer engineered for direct-to-metal and over-primer application on steel and aluminum substrates. Gel time measured in seconds. Tack-free in under 2 minutes. Typical build: 60–125 mils in a single pass. HighLine 510H delivers the combination of tensile strength, elongation, and chemical resistance required for corrosion protection of tanks, structural steel, pipelines, equipment, and marine infrastructure.
Hybrid Polyurea-Polyurethane Systems
For applications where slightly extended working time is preferred, ArmorThane hybrid systems combine polyurea speed with polyurethane processing flexibility. Hybrids are commonly used on architectural metalwork, HVAC equipment, and projects where plural-component spray is not available and roller or brush application is required for some phases.
Aliphatic UV-Stable Topcoats
Aromatic polyurea systems — the standard for industrial metal protection — will chalk and discolor under prolonged UV exposure. This is a cosmetic change that does not affect film integrity or protective performance, but it is not acceptable on visible architectural surfaces or color-specified infrastructure. ArmorThane aliphatic polyurea and polyurethane topcoats maintain color and gloss through years of outdoor UV exposure and are specified over aromatic base coats on bridges, facilities, equipment, and architectural metalwork.
Spray Foam + Polyurea Composites
For pipelines, tanks, and vessels requiring both thermal insulation and corrosion protection in a single system, ArmorThane manufactures spray polyurethane foam that is applied over the metal substrate and then covered with a polyurea protective topcoat. The result is a seamless, impact-resistant composite that insulates the metal from thermal loss and condensation while protecting it from mechanical and chemical damage.
★ Head-to-Head
Metal Coating Comparison — Which System Is Right for Your Project?
The table below compares the five most commonly specified metal coating systems across the performance properties that matter most for industrial, commercial, and infrastructure applications. Use it as a starting framework — always confirm system selection against the specific service environment, substrate condition, application method, and regulatory requirements of your project.
| Property |
Polyurea |
Epoxy |
Polyurethane |
Zinc / Galvanizing |
Alkyd Paint |
| Corrosion Barrier |
Excellent |
Excellent |
Very Good |
Excellent |
Fair |
| Abrasion Resistance |
Excellent |
Very Good |
Good |
Good |
Poor |
| Impact Resistance |
Excellent |
Low |
Good |
Good |
Poor |
| Chemical Resistance |
Excellent |
Excellent |
Very Good |
Limited |
Poor |
| Flexibility / Elongation |
Very High (300–600%) |
Low (<5%) |
Moderate |
Low |
Low |
| Cure Speed (return to service) |
1–24 hours |
12–72 hours |
4–24 hours |
Factory process |
Days |
| UV Stability (outdoor) |
Excellent (aliphatic grades) |
Chalks (aromatic) |
Excellent (aliphatic) |
Good |
Degrades |
| VOC Content |
Zero (100% solids) |
Low–moderate |
Low–moderate |
Zero (galvanizing) |
High |
| Field Repairable |
Yes — spot repair |
Yes |
Yes |
Requires specialist |
Yes |
| Typical Service Life |
20–40+ years |
10–20 years |
10–20 years |
20–70 years |
3–7 years |
Bottom line: Polyurea wins when you need a fast-curing, seamless, flexible, chemically resistant coating on complex metal geometry — tanks, structural steel, equipment, pipelines, and trailers. Epoxy wins for immersion lining where rigidity is acceptable and cost is the primary driver. Galvanizing wins for structural fabrications that can be factory-processed before installation. Alkyd paint belongs on applications where appearance matters more than long-term protection.
▲ Industries Served
Metal Coating Applications by Industry
ArmorThane polyurea and polyurethane metal coatings are in service across every major industrial sector. The application varies by industry, but the underlying requirement is consistent: a seamless, durable, chemically resistant barrier between the metal asset and the environment that will corrode or abrade it.
⚒ Oil, Gas & Petrochemical
Upstream, midstream, and downstream metal assets face the harshest coating service environments on earth: crude oil, sour gas, saltwater, acids, high temperatures, and mechanical abuse. ArmorThane systems are specified for tank farm exteriors, pipeline exterior wraps, secondary containment structures, wellhead equipment, process vessels, and offshore structural steel. Fast return to service is critical in production environments where every hour of downtime has a direct cost.
☌ Infrastructure & Bridges
Bridge structural steel, highway guardrail, sign structures, overhead pipelines, and water towers are all metal assets exposed to atmospheric corrosion, deicing salt, UV radiation, and decades of service life demands. ArmorThane aliphatic polyurea systems with zinc-rich primer underlayers provide multi-decade corrosion protection on infrastructure steel, meeting DOT and FHWA specification requirements.
☢ Marine & Waterfront
Steel sheet piling, bulkheads, dock pilings, boat hulls, barges, and marine structures operate in the most corrosive environment on the planet: salt water, marine atmosphere, tidal splash zones, and biofouling. ArmorThane polyurea builds a seamless waterproof membrane over steel and aluminum marine structures that resists chloride penetration, UV exposure, and the constant mechanical punishment of water, wave, and vessel contact.
⛨ Mining & Mineral Processing
Ore bins, chutes, hoppers, ball mills, conveyor systems, and process vessels in mining operations face the combination of abrasive mineral materials and acidic or alkaline process chemistries. Pure polyurea delivers the abrasion resistance of a hard coating and the chemical resistance of an elastomer in a single system — often replacing epoxy/ceramic tile combinations that fail in the same service at far lower installed cost.
⚓ Water & Wastewater Infrastructure
Water storage tanks, clarifiers, digester covers, aeration basins, and chemical feed equipment in municipal water and wastewater systems are metal or concrete structures that require NSF 61-certified or food-contact-safe coating systems. ArmorThane systems are used for both interior linings (potable water tanks) and exterior protection of above-ground metal infrastructure at treatment plants.
✆ Military & Defense
Vehicles, trailers, containers, fuel systems, aircraft hangars, runway infrastructure, and base storage facilities all require metal coatings that meet demanding military specifications. ArmorThane systems have been installed on U.S. and allied military assets for decades. We manufacture blast-rated, ballistic-rated, and chemical-agent-resistant coating formulations that meet or exceed relevant MIL-SPEC and DoD UFC requirements.
☰ Agriculture & Food Processing
Grain bins, fertilizer storage, chemical handling equipment, processing facility walls and floors, and vehicle assets in agricultural service face UV exposure, corrosive agricultural chemicals, and physical impact. ArmorThane systems resist the full range of agricultural chemicals including anhydrous ammonia, liquid nitrogen, pesticides, and herbicides, while delivering the physical durability required in farm and food processing environments.
⛭ Transportation & Fleet
Truck beds, trailers, box truck interiors, rail car floors, and fleet vehicles are high-value metal assets that deteriorate rapidly without protection from corrosion, impact, and abrasion. The ArmorThane dealer and applicator network offers direct-to-consumer and commercial fleet metal coating services. Spray-applied polyurea bed liners and trailer coatings are among the highest-volume applications in our network.
→ Step-by-Step
Metal Coating Application Process
A polyurea metal coating only performs to specification if the substrate preparation and application are executed correctly. The following steps represent a complete professional installation for a structural steel or industrial equipment application. Every step is a quality checkpoint, not a suggestion.
01
Pre-Job Assessment & Surface Condition Report
The applicator inspects the metal substrate for mill scale, existing coatings, corrosion type and extent, weld quality, and surface condition. Any structural repairs, welding, or mechanical repairs are completed before coating begins. Ambient conditions — temperature, humidity, dew point — are measured and documented.
02
Degreasing & Initial Cleaning
All oil, grease, wax, and soluble salts are removed using SSPC-SP 1 solvent cleaning or pressure washing with appropriate cleaners. Salt contamination is tested and must pass the specified chloride threshold before blasting. Contaminated steel blasted without prior degreasing will simply redistribute contamination into the anchor profile.
03
Abrasive Blast Cleaning
Steel substrates are abrasive blast cleaned to SSPC-SP 10 near-white metal (minimum) using steel grit, steel shot, or a garnet/angular abrasive at the media size and air pressure required to achieve the specified anchor profile (typically 2.5–4.0 mils). Blast-cleaned surfaces must be primed before oxidation begins — typically within 4 hours of blasting in dry conditions, sooner in humid environments.
04
Profile Verification
Surface profile is measured using Testex replica tape (ASTM D4417 Method C) or a digital profilometer. Cleanliness is confirmed by visual comparison to SSPC-VIS 1 or ISO 8501 reference photographs. Dust level is tested per ISO 8502-3. Dew point margin is verified (substrate temperature must be at least 5°F above dew point).
05
Primer Application
An ArmorThane-specified primer is applied by brush, roller, or airless spray to the clean, profiled metal surface. Primer selection is substrate-specific. Steel primers are different from aluminum primers, and neither is interchangeable with concrete or geotextile primers. Primer is allowed to reach the specified tack level before polyurea topcoat is applied. Applying polyurea over wet or uncured primer is a known cause of adhesion failure.
06
Polyurea Topcoat Application
The plural-component proportioner heats and pressurizes the A-side (isocyanate) and B-side (amine resin) materials, meters them at the specified 1:1 ratio by volume, and delivers them to an impingement-mixing spray gun. The applicator applies overlapping passes to build the specified dry film thickness. Typical build is 60–125 mils per pass for pure polyurea systems. Temperature, pressure, ratio, and film build are monitored continuously.
07
Film Thickness Verification
Dry film thickness is measured using a calibrated magnetic pull-off or eddy-current gauge on steel (SSPC-PA 2) or an electronic gauge on aluminum. Measurements are taken in a grid pattern per the specified frequency. Areas below minimum DFT are abraded and recoated. Areas above maximum DFT are documented and reviewed against the TDS.
08
Holiday (Pinhole) Detection
For immersion service, pipeline coating, and secondary containment applications, the cured polyurea film is holiday-tested using a low-voltage wet-sponge tester (below 500 μm DFT) or a high-voltage DC spark tester (above 500 μm DFT) per NACE SP0188. Holidays are located, marked, abraded, and recoated to minimum DFT.
09
Aliphatic Topcoat (UV-Exposed Applications)
For outdoor structures, bridges, architectural metalwork, and any application where color stability and gloss retention are specified, an aliphatic polyurea or polyurethane topcoat is applied over the cured aromatic base coat. The aliphatic topcoat provides UV resistance without affecting the base coat’s corrosion protection or mechanical properties.
10
Documentation & Turnover
The complete application record — surface preparation method, ambient conditions at each stage, primer lot numbers, coating lot numbers, DFT readings, holiday test results, repairs, and as-applied drawing — is assembled and turned over to the owner. This documentation is essential for maintenance planning, insurance, and warranty compliance.
✓ Inspection & Maintenance
Metal Coating Inspection, Maintenance & Service Life
A correctly specified and applied metal coating is not a set-and-forget investment. A documented inspection and maintenance program extends service life, prevents corrosion initiation at film defects, maintains warranty compliance, and provides the documentation that insurers and regulators require. The most cost-effective coating maintenance is the same as the most cost-effective medical care: prevention is cheaper than treatment.
Inspection Frequency
For industrial and commercial metal assets, an annual coating inspection by a qualified coating inspector (NACE/AMPP Coating Inspector CIP Level 1 or higher) is the standard minimum. High-consequence assets — pipelines, bridges, structural steel in aggressive environments, chemical storage — should be inspected annually regardless of apparent condition. Atmospheric exposure assets in mild environments can often extend to biennial inspection with strong maintenance records.
Each inspection documents: visible film condition (blistering, cracking, chalking, delamination, rusting), DFT readings at standard test points, holiday test results on immersion-service areas, substrate condition where visible, and any maintenance performed since the last inspection.
Repair of Polyurea Metal Coatings
Polyurea is field-repairable, which is one of its major advantages over competing metal coating systems. Damaged areas are mechanically abraded (disc or hand grind) to remove loose coating and create a clean, rough surface, re-primed if bare metal is exposed, and recoated with matching polyurea chemistry. When done per the manufacturer’s procedure, the repair bonds to the underlying film and restores the original protective properties — unlike some epoxy and galvanizing repair methods that create weak points at the repair boundary.
Expected Service Life
Polyurea metal coatings on properly prepared and primed steel substrates, maintained through an annual inspection and prompt repair program, regularly achieve 20–40-year service lives in atmospheric service. Immersion and chemical service lives vary with the specific chemistry and exposure; consult ArmorThane technical support for guidance on specific environments. These service lives significantly exceed conventional paint systems (3–7 years to first maintenance) and are competitive with hot-dip galvanizing at a lower installed cost on complex structures.
? Common Questions
Frequently Asked Questions About Metal Coating
What is the best coating for metal?
There is no single “best” coating for all metal — the right choice depends on the metal type, service environment, mechanical and chemical loads, application method, and required service life. For most demanding industrial applications — tanks, structural steel, equipment, pipelines in aggressive service — pure polyurea systems from ArmorThane deliver the best combination of corrosion protection, abrasion resistance, chemical resistance, flexibility, and service life. For interior structural steel in mild atmospheric service, a zinc-rich primer with epoxy intermediate and polyurethane topcoat is a cost-effective three-coat system. Contact ArmorThane technical support to get a recommendation for your specific application.
How long does metal coating last?
Service life depends entirely on the coating system, surface preparation quality, application quality, service environment, and maintenance program. Conventional alkyd paint on steel lasts 3–7 years before first maintenance. Epoxy systems achieve 10–20 years in atmospheric service. ArmorThane polyurea systems on properly prepared and maintained steel regularly achieve 20–40 years in atmospheric service. Hot-dip galvanizing can last 70+ years in rural atmospheric environments. An annual inspection and prompt repair of any film defects are the most effective way to maximize service life of any metal coating.
How do you prepare metal before coating?
Proper metal surface preparation for high-performance coating involves: (1) Solvent cleaning (SSPC-SP 1) to remove oil, grease, and wax; (2) Abrasive blast cleaning to the specified cleanliness standard — SSPC-SP 10 near-white metal is the standard minimum for polyurea, epoxy, and industrial coating systems; (3) Anchor profile measurement to verify the specified depth (typically 2.5–4.0 mils for industrial coatings); (4) Salt and contaminant testing; (5) Dust removal; (6) Dew point verification before primer application. Any steps skipped or done inadequately will reduce coating performance and service life.
Can you spray polyurea directly on metal?
Polyurea requires a primer for direct-to-metal application. The primer is a thin-film coating formulated to bond to the clean, profiled metal substrate and provide a compatible tie coat for the polyurea topcoat. Applying polyurea directly over unprimed metal is a known cause of adhesion failure. ArmorThane supplies steel-specific and aluminum-specific primers that are engineered to work with our polyurea systems. The correct primer, applied correctly, achieves pull-off adhesion values that exceed the cohesive strength of the substrate.
What is the difference between polyurea and polyurethane for metal coating?
Both polyurea and polyurethane are isocyanate-based elastomeric coatings with similar chemical families. The key difference is reaction chemistry: pure polyurea reacts an isocyanate with an amine resin, producing a very fast gel time (seconds) and tack-free time (minutes). Pure polyurethane reacts an isocyanate with a polyol, producing slower cure and greater sensitivity to moisture during cure. Hybrid systems combine amine and polyol components to achieve intermediate properties. For metal coating, pure polyurea offers faster return to service and less moisture sensitivity. Aliphatic polyurethane topcoats are the standard UV-stable finish over aromatic polyurea base coats on outdoor metal.
Does polyurea rust or corrode metal?
No. Polyurea itself is inert to corrosion — it is a polymer, not a metal. A properly applied polyurea coating prevents rust by forming a continuous, seamless barrier between the steel substrate and the oxygen, moisture, salts, and chemicals that cause corrosion. The key word is “properly applied”: the coating must be pinhole-free (holiday-tested), correctly bonded to the substrate through the primer layer, and at sufficient film thickness that the substrate has no exposed metal. Corrosion under a polyurea coating is a sign of adhesion failure or a holiday in the film, not a coating chemistry problem.
How thick should a metal coating be?
Minimum dry film thickness (DFT) depends on the coating system and the service environment. For atmospheric corrosion protection on structural steel, three-coat zinc/epoxy/polyurethane systems are typically specified at 6–12 mils total DFT. For polyurea direct-to-metal systems in industrial service, 60–125 mils in a single pass is standard. For immersion service, secondary containment, and chemical-resistant linings, 80–250 mils may be specified. Always refer to the current ArmorThane Technical Data Sheet for the minimum and maximum DFT appropriate for the selected system and service condition.
What metals can be coated with polyurea?
ArmorThane polyurea systems can be applied to steel (carbon steel and stainless), aluminum, galvanized steel, cast iron, and most alloy metals with the appropriate primer. The primer selection is substrate-specific: steel primers, aluminum primers, and galvanized steel primers are different products. The substrate must be clean, dry, and at the specified surface profile. Contact ArmorThane technical support for primer recommendations when coating unusual substrates or complex multi-metal assemblies.
Is polyurea coating UV resistant?
Aromatic polyurea systems — the standard chemistry for industrial metal protection — will chalk and amber under UV exposure. This is a cosmetic change that does not affect the coating’s protective performance or structural integrity, but the color and gloss degrade. For applications where color stability and long-term appearance matter, ArmorThane aliphatic polyurea or aliphatic polyurethane topcoats are applied over the aromatic base coat. Aliphatic topcoats maintain color and gloss through years of direct UV exposure and are the standard specification for bridges, architectural metalwork, and outdoor equipment.
How much does metal coating cost?
Metal coating cost is project-specific and depends on substrate access, surface preparation required, coating system selected, film thickness, project size, and regional labor rates. As a rough framework: conventional paint on accessible structural steel runs $3–$7 per square foot installed; three-coat industrial systems (zinc/epoxy/polyurethane) run $10–$20 per square foot; polyurea direct-to-metal systems run $8–$20 per square foot depending on film thickness and project conditions. Total lifecycle cost — accounting for service life and recoating intervals — consistently favors polyurea over competing systems in demanding service. Request a project-specific quote through ArmorThane’s applicator network.
Can metal coating be applied in cold weather?
ArmorThane polyurea can be applied in temperatures down to freezing and, with appropriate precautions, below. The substrate must be dry and at least 5°F above the dew point. Material temperatures must be maintained at the application requirements. Cold-weather application requires heated spray equipment, heated hoses, and often temporary enclosures to maintain ambient and substrate temperature in the application zone. Experienced applicators with appropriate equipment can apply polyurea year-round in most climates. Contact ArmorThane to discuss your cold-weather application requirements.
References & Further Reading
- AMPP (formerly NACE International / SSPC). SSPC-SP 1, SP 6, SP 10, SP 5 Surface Preparation Standards. AMPP.org
- AMPP. NACE SP0188: Discontinuity (Holiday) Testing of New Protective Coatings on Conductive Substrates. AMPP.org
- ASTM International. Standard Test Methods D412 (Tensile), D2240 (Hardness), D624 (Tear), D4541 (Pull-off Adhesion), D4060 (Abrasion Resistance), D4417 (Surface Profile). ASTM.org
- ISO 8501-1. Preparation of Steel Substrates Before Application of Paints and Related Products — Visual Assessment of Surface Cleanliness. ISO.org
- NACE International (AMPP). Corrosion Costs and Preventive Strategies in the United States. Publication FHWA-RD-01-156.
- ArmorThane USA Inc. HighLine 510H Technical Data Sheet. ArmorThane.com
- U.S. Army Corps of Engineers. Engineer Manual EM 1110-2-3400: Painting: New Construction and Maintenance.
About ArmorThane. ArmorThane USA Inc. has been manufacturing polyurea and polyurethane protective coatings, spray foam systems, and plural-component application equipment in Springfield, Missouri since 1989. We operate as a direct manufacturer, not a franchise network. Our coatings and equipment are installed in the field by a global network of trained applicators across North America and more than 30 countries. Technical support is available 24/7 at (417) 831-5090.
